Seasonal Cycle

In this study we use a modified version of the ecosystem model Boreal Ecosystem Productivity Simulator (BEPS) to simulate gross primary productivity (GPP) derived from measured CO 2 flux at the Takayama site, which is characterized by a broadleaf deciduous secondary forest. The period of simulation is from 1998 to 2002. The performance of the model is assessed in its ability to reproduce seasonal and inter-annual variations in the derived GPP. Given appropriate vegetation parameters and meteorological conditions for the site, we find that the model can simulate seasonal changes and inter-annual variability of GPP that are in close agreement with those derived from the eddy covariance CO 2 flux measurements. Estimated annual GPPs (in gC m À2 ) are 1171 (1998), 1024 (1999), 1274 (2000), 1200 (2001), and 1243 (2002). (Positive GPP is defined as ecosystem assimilation of CO 2 .) Although the inter-annual variability of the seasonal cycle and its upward trend are simulated relatively well, the model tends to overestimate GPP, particularly from 2000 to 2002 when the measured leaf area index (LAI) during the growing season was relatively high. Furthermore, due to certain missing phenological mechanisms in the model, it tends to overestimate photosynthetic absorption during the latter half of the growing season. Also, the model does not resolve the understory of dense evergreen dwarf bamboo at the site, thus failing to catch the start of photosynthetic activity by the understory before the leaf emergence of the woody component takes place in the spring. Results indicate that the observed inter-annual variability in GPP at the Takayama site has been influenced mostly by changes in LAI.

Changes in solar activity modulate the galactic cosmic ray flux, and in turn, the production rate of 10Be in the earth's atmosphere. The best archives of past changes in 10Be production rate are the polar ice cores. Key challenges in interpreting these archives ...

The application of a one-dimensional ecosystem model to a water column in front of the Po Prodelta area in the Northern Adriatic Sea is illustrated here. Validation was carried out for pelagic nutrients and phytoplankton biomasses by comparing simulations with historical data. Calibration was limited to the sediment parameters and to the suspended inorganic matter data from recent PRISMA-I (Programma di RIcerca e Sperimentazione per il Mare Adriatico) data sets. Primary production and nutrient abundance is found to be in overall agreement with climatological observations at the seasonal time scales. Model-data discrepancies are interpreted in the light of model assumptions. Main conclusions concern the importance of the inorganic suspended matter concentrations in determining the seasonal cycle of primary producers hinting to a strong light limitation in algal growth in this river dominated area. The need for further improvements in the pelagic dynamical processes of the silica cycle is also discussed.

The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction ACPD

The performance of 18 coupled Chemistry Climate Models (CCMs) in the Tropical Tropopause Layer (TTL) is evaluated using qualitative and quantitative diagnostics. Trends in tropopause quantities in the tropics and the extratropical Upper Troposphere and Lower Stratosphere (UTLS) are analyzed. A quantitative grading methodology for evaluating CCMs is extended to include variability and used to develop four different grades for tropical tropopause temperature and pressure, water vapor and ozone. Four of the 18 models and the multi‐model mean meet quantitative and qualitative standards for reproducing key processes in the TTL. Several diagnostics are performed on a subset of the models analyzing the Tropopause Inversion Layer (TIL), Lagrangian cold point and TTL transit time. Historical decreases in tropical tropopause pressure and decreases in water vapor are simulated, lending confidence to future projections. The models simulate continued decreases in tropopause pressure in the 21st ...

A knowledge of the balance between plankton gross primary production.(GPP) and community respiration (CR) in the open ocean is vital to the accurate determination of the global carbon cycle, yet the paucity of open ocean measurements severely limits our understanding. This study measured GPP, net community production, dark CR, and size-fractionated primary production in the upper 200 m of a 12,100 km latitudinal (32°S-48°N) transect in the Eastern Atlantic Ocean during May and June 1998. This comprehensive data set, which spans five contrasting plankton regimes, including two open ocean oligotrophic provinces, is used to derive a GPP: CR relationship, which suggests that net heterotrophy (GPP < CR) prevails in the eastern Atlantic when primary production falls below -100 mmol 02 m-2 d-t . The predictive capability of this relationship is compared with that of the only other published relationship based on similar methodologies and is found to give a more representative description of the autotrophic (GPP > CR) to heterotrophic seasonal cycle in the Bay of Biscay. This improved predictive power is attributed to the increased representativeness of the current data set. Specifically, the interpretation suggests that the influence of community structure on net ecosystem metabolism implies that prediction of GPP: CR balances in pelagic ecosystems can be best achieved by use of a data set that covers a wide range of community structure and not only a wide range in the magnitude of primary production. The significant contribution of the marine biota to the global carbon cycle (e.g., Sarmiento and Siegenthaler 1992) ultimately results from the balance between gross primary production (GPP) (all photosynthesis independent of its fate) and community respiration (CR) (the oxidative consumption of organic matter by autotrophic and heterotrophic organ-

A primitive equation, hydrostatic, terrain-following coordinate ocean general circulation model Ž . OGCM is used to investigate the mean water mass pathways from the subtropics to the tropics in the Atlantic Ocean. The OGCM is used in a fully realistic configuration of the Atlantic, from 308S to 658N, with realistic bathymetry. Surface forcings are provided by the COADS climatology. A non-eddy-resolving numerical simulation is analyzed with 3r48 horizontal resolution and 20 terrain-following vertical levels. The primary objective of this study is to assess the theoretical framework extending the ventilated thermocline theory to the equator in the context of the numerical calculation, and to establish whether the predictions of a steady-state theory can be verified in a time-dependent simulation, in which rectified seasonal effects on the time mean yearly circulation may be important. The Bernoulli function is evaluated on isopycnal surfaces outcropping in the subtropics in both hemispheres and floats are injected at different northern and southern latitudes. In both hemispheres, the interior flow velocities are parallel to the Bernoulli streamlines that are significantly modified by inertia only very near the equator and on the Equatorial UnderCurrent Ž . EUC . In the Northern Atlantic, pathways from the subtropics to the tropics exist for the isopycnal surfaces outcropping at 20-228N. The injected floats reach the EUC following a zigzag pattern

The isotope 18O in CO2 is of particular interest in studying the global carbon cycle because it is sensitive to the processes by which the global land biosphere absorbs and respires CO2. Carbon dioxide and water exchange isotopically both in leaves and in soils, and the 18O character of atmospheric CO2 is strongly influenced by the land biota, which should constrain the gross primary productivity and total respiration of land ecosystems. In this study we calculate the global surface fluxes of 18O for vegetation and soils using the SiB2 biosphere model coupled with the Colorado State University general circulation model. This approach makes it possible to use physiological variables that are consistently weighted by the carbon assimilation rate and integrated through the vegetation canopy. We also calculate the air‐sea exchange of 18O and the isotopic character of fossil emissions and biomass burning. Global mean values of the isotopic exchange with each reservoir are used to close t...

Synthetic Aperture Radar (SAR) images of Titan&#39;s north polar region reveal quasi‐circular to complex features which are interpreted to be liquid hydrocarbon lakes. We investigate methane transport in Titan&#39;s hydrologic cycle using the global distribution of lake features. As of May 2007, the SAR data set covers ∼22% of the surface and indicates multiple lake morphologies which are correlated across the polar region. Lakes are limited to latitudes above 55°N and vary from &lt;10 to more than 100,000 km2. The size and location of lakes provide constraints on parameters associated with subsurface transport. Using porous media properties inferred from Huygens probe observations, timescales for flow into and out of observed lakes are shown to be in the tens of years, similar to seasonal cycles. Derived timescales are compared to the time between collocated SAR observations in order to consider the role of subsurface transport in Titan&#39;s hydrologic cycle.

A clear trend of tropical precipitation changes induced by global warming is found in hemispherical averages of most climate model simulations as well as from observation. It is observed that in response to global warming, an asymmetric pattern develops between tropical precipitation changes in the northern and southern hemispheres, and this asymmetry is locked with the seasonal cycle of tropical convection. In boreal summer (winter), the northern hemispherical average departure from tropical mean increases (decreases), while the departure of the southern hemispherical average decreases (increases). This implies an enhanced seasonal precipitation range between rainy and dry seasons and an increased precipitation difference between northern and southern hemispheres.

Monthly plankton sampling was carried out at three stations on the west coast of Inhaca Island, southern Mozambique, from August 1994 to August 1995. Sampling included water mass physical parameters, nutrients, chlorophyll and zooplankton with nets of 125 and 330 um pore aperture. Nutrient concentration has shown maxima during the summer months, where rain provides the maximum outflow of rivers discharging into Maputo Bay. Following the nutrient peak, chlorophyll a has shown maxima around the month of April, with another minor peak in September, when temperature begins to increase. Zooplankton densities followed closely the phytoplankton peaks, especially small herbivorous taxa and larval stages, such as gastropod and bivalve larvae.

The atmospheric composition of the central North Atlantic region has been sampled using the FAAM BAe146 instrumented aircraft during the Intercontinental Transport of Ozone and Precursors (ITOP) campaign, part of the wider International Consortium for Atmospheric Research on Transport and Transformation (ICARTT). This paper presents an overview of the ITOP campaign. Between late July and early August 2004, twelve flights comprising 72 hours of measurement were made in a region from approximately 20 to 40°W and 33 to 47°N centered on Faial Island, Azores, ranging in altitude from 50 to 9000 m. The vertical profiles of O 3 and CO are consistent with previous observations made in this region during 1997 and our knowledge of the seasonal cycles within the region. A cluster analysis technique is used to partition the data set into air mass types with distinct chemical signatures. Six clusters provide a suitable balance between cluster generality and specificity. The clusters are labeled as biomass burning, low level outflow, upper level outflow, moist lower troposphere, marine and upper troposphere. During this summer, boreal forest fire emissions from Alaska and northern Canada were found to provide a major perturbation of tropospheric composition in CO, PAN, organic compounds and aerosol. Anthropogenic influenced air from the continental boundary layer of the USA was clearly observed running above the marine boundary layer right across the mid-Atlantic, retaining high pollution levels in VOCs and sulfate aerosol. Upper level outflow events were found to have far lower sulfate aerosol, resulting from washout on ascent, but much higher PAN associated with the colder temperatures. Lagrangian links with flights of other aircraft over the USA and Europe show that such signatures are maintained many days downwind of emission regions. Some other features of the data set are highlighted, including the strong perturbations to many VOCs and OVOCs in this remote region.

A solar radiometer has been used to monitor solar irradiance at eight discrete wavelengths, From these monochromatic measurements at varying zenith angles the total optical depth has been deduced by a computerized curve-fitting method. A unique technique will be described whereby the ozone absorption optical depths, and hence total ozone content of the atmosphere, can be inferred directly from the spectral variation of total optical depth. This procedure permits a systematic determination of total ozone content on a daily basis when other measurements are not available. Using the ozone absorption optical depths determined in this manner, the values of aerosol optical depth may be obtained more accurately by subtracting the molecular scattering and estimated ozone absorption contributions from the total optical depth. A technique is also described for estimating the absorption optical depths at wavelengths where additional molecular absorption other than ozone occurs. Results are presented as 1) daily values of total ozone content and 2) molecular absorption optical depths due to water vapor and oxygen at two of the radiometer wavelengths. The total ozone content exhibits the characteristic seasonal cycle with peak values in April.

Altimetry data have proven themselves essential for the early detection, analysis and monitoring of large scale tropical anomalies associated with El Nin ˜o in the Pacific. Warm events in the Atlantic are much weaker than in the Pacific and are partially masked by the strong seasonal cycle. Satellite altimetric data permits one to estimate the zonal sea surface slope variations at the equator in the Atlantic with sufficient accuracy for resolving interannual sea surface slope variations. The altimetry-derived slope is here shown to detect Atlantic warm events. For all warm events, anomalies in sea surface slope tend to lead SST. In the mid-1990sÕ, the equatorial interannual variability is dominated by 17-month period events which exhibit the structure observed in local coupled ocean-atmosphere warm events (zonal wind stress weakening and zonal surface slope relaxation, warm SST, excess precipitation). The frequency of occurrence of these Atlantic warm events is seen to have increased during the mid-1990s.

We provide a review description of atmospheric inversion methods for the determination of fluxes of long-lived trace gases based on measurements of atmospheric concentration. Emphasis is given to technical aspects of inversion settings, which are crucial to inter-compare and understand inversion results. We briefly sketch the formalism used in such methods, then provide a summary of major currents in research and contemporary problems. Most attention is given to carbon dioxide (CO 2 ) which poses the threat of future climate change. Therefore, there is keen interest in better understanding where and when CO 2 emitted by the combustion of fossil fuels is reabsorbed by land ecosystems and oceans. Using the information contained in concentration fields observed from ground-based networks and from upcoming satellite observations in order to constrain the geographic distribution of surface fluxes is an inverse problem; it consists of finding a set of fluxes that optimally matches the observations available. We review the application of inverse methods to quantify the distribution of the sources and sinks of CO 2 at the surface of the Earth based on global measurements of atmospheric concentration and three-dimensional models of atmospheric transport. We describe the use of topdown atmospheric inversion methods in terms of numerical transport modeling and atmospheric observation networks, and detail some of the currently important issues in assigning uncertainties.

The space-time variations of the carbon budget at the Earth's surface are highly variable and quantifying them represents a major scientific challenge. One strategy consists in inferring the carbon surface fluxes from the atmospheric concentrations. An inversion scheme for the hydrocarbon oxidation chain, that includes CO and CH 4 , is presented here with a focus on the African continent. It is based on a variational principle. The multi-tracer system has been built as an extension of a system initially developed for CO 2 and includes a new simplified non-linear chemistry module. Individual in situ measurements of methyl-chloroform and individual retrievals of CO concentrations from the Measurements Of Pollution In The Troposphere (MOPITT) spaceborn instrument have been processed by the new system for the period 2000-2006 to infer the time series of CO emissions at the resolution of 2.5 • ×3.75 • (latitude, longitude). It is shown that the analysed concentrations improve the fit to five independent surface measurement stations located in or near Africa by up to 28% compared to standard inventories, which confirms that significant information about CO emissions can be obtained from MOPITT data. In practice, the inversion reduces the amplitude and the interannual variability of the seasonal cycle in the northern part of Africa, with a longer burning season. In the southern part, the inversion mainly shifts the emission peak by one month later in the season, consistent with previously-published inversion results.

This article documents the widespread absence of sessile species in bedrock intertidal habitats at the head of the St. Lawrence Estuary, a large macrotidal estuary located in eastern Canada. Extensive observations revealed that no seaweeds or sessile invertebrates occurred anywhere (including cracks and crevices) on substrate areas that become exposed to the air during low tides. Only one sessile species, a green filamentous alga, was found submerged in tidepools. The lack of truly marine sessile species is likely explained by the very low water salinity of this coast, while the absence of sessile freshwater species on intertidal substrates outside of tidepools likely responds to a combination of oligohaline conditions during high tides and daily exposures to the air during low tides, which freshwater species are typically not adapted to. Influences of winter ice scour and coastal suspended sediments are likely secondary. Experimental research could unravel the interactive effects of these abiotic stressors. Overall, this "intertidal desert" could be a useful model system to further explore the boundaries of life on our planet.

Using a multi-satellite method, employing passive and active microwave along with visible and infrared observations developed to estimate monthly inundation extent at global scale, this study investigates the response of river discharge to seasonal flood change in the large Siberian watersheds. The seasonal cycle and variations of inundation extent over the Ob, the Yenissey, and the Lena basins for the period 1993-2000 show different spatial and temporal behaviors due to different climate and permafrost conditions. Using in-situ discharges collected at the outlets of the three basins, we analyze and quantify the relationships between the river streamflow and the monthly satellite-derived inundation extent during the spring/summer periods. Furthermore, we analyze extreme (high/low) streamflow cases for some years and the associated inundation conditions for the three watersheds and link these cases with other climatic parameters such as the snow water equivalent, temperatures, and precipitation. The results of this study demonstrate that the monthly multi-satellite-derived inundation dataset brings a new useful tool for better understanding both the streamflow processes and the description of the snow-inundationrunoff relations in data scarce areas like the remote Arctic river basins.

1 ]U sing as uite of satellite observations, including passive and active microwavea long with visible and infrared observations developed to estimate wetlands on a global scale, the present study examine wetlands spatial and temporal dynamics over the Indian subcontinent, ar egion subject to an annual monsoon. Monthly wetlands extent estimateso ver a2 -year (1993 -1994) period and their consistencya re analyzed using independent data sets, such as rainfall rate in-situ rain-gauge observations and the Global Precipitation Climatology Project product, as well as river water levels derived from radar altimeter observations. The extent variations show agood agreement with the raingauge data, ahigh correlation with the GPCP rain data and a similar seasonal cycle with the altimeter estimates over the 2 years. This case study evaluation shows the potential of the remote sensing to give spatial-temporalc onsistent information on thev ariability of flooded areas and encourages the development of longer satellite wetlands estimates.

We improved a process‐oriented biogeochemical model of carbon and nitrogen cycling in grasslands and tested it against in situ measurements of biomass and CO2 and CH4 fluxes at five European grassland sites. The new version of the model (PASIM) calculates the growth and senescence of aboveground vegetation biomass accounting for sporadic removals when the grassland is cut and for continuous removals when it is grazed. Limitations induced by high leaf area index (LAI), soil water deficits and aging of leaves are also included. We added to this a simple empirical formulation to account for the detrimental impact on vegetation of trampling and excreta by grazing animals. Finally, a more realistic methane emission module than is currently used was introduced on the basis of the quality of the animals&#39; diet. Evaluation of this improved version of PASIM is performed at (1) Laqueuille, France, on grassland continuously grazed by cattle with two plots of intensive and extensive grazing ...

Previously published stable isotopic data on benthic foraminiferal species from a Holocene sequence in the Celtic Sea have been interpreted in terms of the progressive replacement of a tidally mixed by a stratified water mass. Offsets in the 6180 data between Ammonia batavus and Quinqueloculina seminu- luin were attributed to a 'seasonal effect' in which these two species were hypothesized to have calcified at different times of the year. The aims of this study were to test the hypotheses (1) that benthic foraminiferal stable isotope records from across the Celtic Sea front reflect seasonal stratification and (2) that offsets in the oxygen isotope record between different species are the result of the postulated seasonal effect. Hypo- thesis 1 was tested through investigation of live and dead benthic foraminiferal and bottom-water 6180 and f X13C sampled in transects across the Celtic Sea front from mixed through frontal to stratified water masses. Measurements of bottom-water salinity enabled a mixing-line equation to be developed for this area enabling quantitative reconstructions of bottom-water temperature from the isotopic data. Samples from , ,/ stratified settings are characterized by heavier 618Oforam and lighter 3Cf oram values than the mixed samples. Offsets in l180foram between A. batavus and Q. seminuluni support the notion of the seasonal effect. A. batavus produces values close to equilibrium while Q. seminulum overestimates temperature by up to 2°C A and this might explain some of the offset observed between the two species observed in the palaeodata. Comparison of the 6'8 Ofram data with measured seasonal temperature cycles from mixed and stratified RESEARCH localities in the Celtic Sea demonstrates that, while most foraminifera calcify during the summer months, different species calcify at, or are preserved from, different times within this warm part of the seasonal cycle; Q. seminulum calcifies during September when peak bottom-water temperatures occur, while A. batavus calcifies during September in stratified localities, but during spring or early summer in mixed localities. This study confirms the interpretation of the 6180 palaeodata from the Celtic Sea as a palaeostratification record and demonstrates that 6180 data from shelf-sea cores can be used to supplement benthic foraminiferal assemblages as a tool for reconstructing the long-term dynamics of seasonal stratification.

polar stratospheric clouds (PSCs) were observed in the absence of conditions conducive to generation by topographic gravity waves. The possibility is explored that PSCs can be generated by inertia gravity waves (IGW) radiating from breaking synoptic-scale Rossby waves on the polar front jet. The aerosol features on 7 and 12 December are selected for comparison with theory and with simulations using the University of Wisconsin Nonhydrostatic Modeling System (UWNMS). Consistent with Rossby adjustment theory, a common feature in the UWNMS simulations is radiation of IGW from the tropopause polar front jet, especially from sectors which are evolving rapidly in the Rossby wave breaking process. Packets of gravity wave energy radiate upward and poleward into the cold pool, while individual wave crests propagate poleward and downward, causing mesoscale variations in vertical motion and temperature. On 12 December the eastbound DC-8 lidar observations exhibited a fairly uniform field of six waves in aerosol enhancement in the 14-20 km layer, consistent with vertical displacement by a field of IGW propagating antiparallel to the flow, with characteristic horizontal and vertical wavelengths of $300 and $10 km. UWNMS simulations show emanation of a field of IGW upward and southwestward from a northward incursion of the polar front jet. The orientation and evolution of the aerosol features on 7 December are consistent with a single PSC induced by an IGW packet propagating from a breaking Rossby wave over western Russia toward the northeast into the coldest part of the base of the polar vortex, with characteristic period $9 hours, vertical wavelength $12 km, and horizontal wavelength $1000 km. Linear theory shows that for both of these cases, IGW energy propagates upward at $1 km/hour and horizontally at $100 km/hour, with characteristic trace speed $30 m/s. The spatial orientation of the PSC along IGW phase lines is contrasted with the nearly horizontal filamentary structures in the PSC, which are indicative of flow streamlines. It is suggested that vertical displacement is a crucial factor in determining whether a PSC will form and that most PSCs are relatable to specific synoptic and mesoscale motions.

A baixada de Jacarepaguá (RJ/Brasil) vem sofrendo há pelo menos quatro décadas um processo desordenado de ocupação urbana e industrial, o que tem se refletido em mudança na qualidade da água e na incidência de florações de cianobactérias no Complexo Lagunar de Jacarepaguá (CLJ). O presente estudo reuniu uma série de dados temporais objetivando avaliar a qualidade hídrica da Lagoa de Jacarepaguá (LJ) através do monitoramento físico (pH, transparência da água e temperatura), químico (salinidade, O.D. e clorofila a) e da comunidade planctônica. Foi também analisado a concentração de microcistinas no pescado comercializado na região. Os dados foram divididos em três períodos de acordo com os diferentes ciclos sazonais estudados: PI (ago/96 a set/97), PII (jan/99 a nov/99) e PIII (fev/07 a jan/08). Dominância de cianobactérias ocorreu na maior parte do tempo, intercalada por pulsos de maior diversidade fitoplanctônica, observados a partir de 1999 (PII e III). Esta diversidade foi representada pelas clorofíceas, diatomáceas, prasinoficeas e criptoficeas. Foi interessante notar que a dinâmica observada em 1999 tenha se repetido quase 10 anos depois, o que sugere uma tendência sazonal de estruturação da comunidade no CLJ. O desaparecimento da floração coincidiu com épocas de menores temperaturas, sugerindo ser esse um importante fator regulador da dinâmica observada. A LJ apresentou uma elevada abundância zooplanctônica, com baixa diversidade de espécies. Durante alguns meses, as concentrações de microcistinas encontradas nos músculos dos peixes estiveram acima dos valores recomendados pela OMS para consumo humano.

We investigate the seasonal sea surface height (SSH) variability on large spatial scales in the North Atlantic by using both a numerical simulation and in situ data. First, an ocean general circulation model is run with daily forcing from the European Centre for Medium-Range Weather Forecasts reanalysis. We evaluate the different contributions to the seasonal SSH variability resulting from the surface heat fluxes, advection, salt content variability, deep ocean steric changes, and bottom pressure variability. These terms are compared with estimates from in situ data. North of 20øN, there is an approximate balance between hQ, the air-sea heat flux induced changes in steric height, and SSH variability. The next important component is the advection (its contribution to the annual amplitude is of the order of 1 cm except near the western boundary); other contributions are found to be smaller. Between 10øN and 10øS the advection variability induced by the seasonal wind stress cycle is the primary source of SSH variability. We then compare the sea surface height annual harmonic from TOPEX/Poseidon altimetry with the steric effect from the heat flux and with model and/or in situ estimates of the other terms. In many areas north of 20øN the balance between h and the altimetric SSH seasonal cycle is closed within the Q uncertainty limit of each of the terms of the SSH budget. However, h o and the SSH do not balance each other in the eastern North Atlantic, and the results are sensitive tb the choice of the heat flux product, suggesting that significant errors, typically 20-40 W m -2 for the seasonal cycle amplitude, are present in the meteorological model heat fluxes. 1. Introduction Gill and Niiler's [1973] analysis of seasonal variations of upper ocean temperature identified air-sea heat exchange as the prime agent of the seasonal oceanic heat content change. This is particularly expected to hold for large spatial scales away from strong currents and outside of the tropics and has been verified at a few locations with good sampling, for example, in the northeastern Pacific at station Papa [ Tabata et al., 1986] and at other weather ship sites [Alexander and Deser, 1995]. Direct investigations of the large-scale ocean heat budget also seem to confirm this hypothesis both in the Pacific [Moisan and Niiler, 1998] and in the Atlantic [Cayan, 1992].

The climatological seasonal cycle of sea surface temperature (SST) in the tropical Pacific is simulated using a newly developed upper ocean model. The roles of vertical mixing, solar radiation, and wind stress are investigated in a hierarchy of numerical experiments with various combinations of vertical mixing algorithms and surface‐forcing products. It is found that the large SST annual cycle in the eastern equatorial Pacific is, to a large extent, controlled by the annually varying mixed layer depth which, in turn, is mainly determined by the competing effects of solar radiation and wind forcing. With the application of our hybrid vertical mixing scheme the modelsimulated SST annual cycle is much improved in both amplitude and phase as compared to the case of a constant mixed layer depth. Beside the strong effects on vertical mixing, solar radiation is the primary heating term in the surface layer heat budget, and wind forcing influences SST by driving oceanic advective processes ...

Rotational stocking is a component of intensive pasture management and involves the systematic movement of animals among paddocks to optimize harvest of digestible nutrients. The optimum period of residence time for beef cattle in a paddock has not been researched in Atlantic Canada. A series of experiments were conducted at the Nova Scotia Agricultural College during the 1994, 1995, and 1996 grazing seasons to determine if short residence times (1 day) or longer residence times (6 or 7 days) encouraged higher average daily gains (ADG) in beef cattle. In 1994 and 1995, Hereford steers were used, and in 1996, Hereford heifers were used to compare the effects of daily and weekly residence times. In the mid to late season of 1994, a preliminary study with fewer replicates than in 1995 and 1996 indicated that the steers with a daily and weekly residence time gained 1.18 and 1.09 kg animal -1 day -1 , respectively. Based on these results the project was expanded with the hypothesis that daily residence times result in higher average daily gains compared with weekly residence times. In both 1995 and 1996, cattle ADG for the first part of the season was higher with weekly residence times and similar near mid-season. Near the end of the grazing season the trend reversed with the daily residence time producing a higher cattle ADG. The results of this study indicate that animal performance could be maximized by long rotation cycles during periods of rapid forage growth and short rotation cycles during periods of slow forage growth. In all years, animals were finished on pasture with no visible yellow fat.

A set of multiply nested atmospheric (The Penn State/NCAR Mesoscale Modeling system-MM5) and oceanic (Regional Ocean Modeling System-ROMS) models has been developed to investigate ecosystem forcing as part of the US. GLOBEC program. This study focuses on the most finely nested oceanic model in the hierarchy, that of the coastal Gulf of Alaska (CGOA) during 2001-2002, and compares the model's results to data collected by GLOBEC investigators. The 3-km resolution model realistically generates two physical features needed to reproduce the CGOA ecosystem: the cross-shelf water mass structure on the Seward Shelf, and the seasonal cycle of vertical structure. In addition, the temporal variability of currents and tracer fields generated by the model is greatly improved compared to previous work, as is the resolution of the Alaska Coastal Current (ACC). However, the treatment of the line-source freshwater source along the coast of Alaska still presents difficulties, because the model cannot resolve the many inlets and fjords where mixing takes place initially. This issue is investigated by testing the model's sensitivity to various forcing mechanisms which could compensate for this weakness, such as the addition of tidal mixing, the use of finely resolved winds, and the use of brackish runoff rather than purely freshwater for the line-source.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The space-time variation of phytoplankton pigments in the western Intra-Americas Sea (IAS), in the vicinity of the island of Cuba, is examined using digital images obtained with the Coastal Zone Color Scanner sensor flown aboard the Nimbus 7 satellite from 1978 to 1986. The results are compared to historical in situ hydrographic observations. A marked seasonality in pigment concentration was observed in waters around Cuba, with an average of 0.07 mg m -3 in summer (April-September) and 0.13 mg m -3 during winter (October-March). The range of variation in pigment concentration was larger in the Gulf of Mexico relative to the western Caribbean Sea. We identified four biogeographical areas on the basis of groups of pixels with similar patterns of time variability. These are area I: southwest of Cuba, Yucatan Channel, and Florida Strait; area II: central Gulf of Mexico; area III: east of Cuba; and area IV: central Caribbean Sea, south of Jamaica and Hispaniola. Two major meteorological events led to anomalies in the seasonal cycle of pigment concentrations. During E1 Nifio-Southern Oscillation (ENSO) of 1982-1983, positive anomalies were observed in the pigment concentration in the western IAS during winter months. This was associated with intense mixing of the water column by higher-frequency and stronger winds associated with cold fronts. ENSO 1982-1983 therefore had a fertilizing effect on the IAS region. Another positive anomaly was observed in 1980-1981, a non-ENSO period that featured higher hurricane and extratropical low-pressure activity. 1. Introduction There are surprisingly few studies that address patterns in the abundance of phytoplankton in the Intra-Americas Sea (IAS), which includes the Caribbean and the Gulf of Mexico. Perhaps this is because this semienclosed tropical basin is traditionally considered to be oligotrophic [Margalef, 1969; Conedor, 1977]. On the basis of studies of Coastal Zone Color Scanner (CZCS) satellite data, however, we know that the Gulf of Mexico undergoes pronounced seasonal variation in phytoplankton standing stocks. This seasonality is driven in summer by high stability of the water column (low pigment concentrations) and by convective cooling and stronger winds during winter (high concentrations) [Maller-Karger et al., 1991; Melo et al., 1995]. The southeastern Caribbean also experiences seasonal variability in pigment abundance, with wind-driven upwelling leading to high concentrations along its southern margin during boreal winter and spring. The widespread plume formed by the discharge of the Orinoco River leads to higher phytoplankton biomass and dissolved organic concentrations

The Doppler shifts of meteor echoes measured by the SuperDARN HF radar network have been used in several studies to observe neutral winds in the upper mesosphere and lower thermosphere region. In the absence of accurate height information for individual meteors, it has been necessary to assume a statistical mean meteor layer where the variations in altitude were not correlated to changes in the horizontal winds. Observations of spectral width distribution variations made by the radars allow an independent determination of the systematic error in the height. We have investigated the dependence of this distribution on a number of factors including the radar geometry, diurnal and seasonal cycles, variations in solar UV irradiance and geomagnetic activity. Changes in the altitude of the mean meteor layer observed at different radar ranges provide us with some insight into the structure of the upper mesosphere and the lower thermosphere within which the meteors are being ablated. An examination of the spectral widths, as measured by the CUT-LASS Finland radar, in the days preceding and following a Storm Sudden Commencement in April 1997, illustrates how the spectral properties of the observed region can be affected. The variations in the widths were consistent with model calculations of the changes to the temperature profile over this interval. Further refinements in the determination of the spectral width are outlined for future experiments.

We investigated the large-scale connection between African aerosol and precipitation in the West African Monsoon (WAM) region using 8-year (2000-2007) monthly and daily Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol products (aerosol optical depth, fine mode fraction) and Tropical Rainfall Measuring Mission (TRMM) precipitation and rain type. These high-quality data further confirmed our previous results that the large-scale link between aerosol and precipitation in this region undergoes distinct seasonal and spatial variability. Previously detected suppression of precipitation during months of high aerosol concentration occurs in both convective and stratiform rain, but not systematically in shallow rain. This suggests the suppression of deep convection due to the aerosol. Based on the seasonal cycle of dust and smoke and their geographical distribution, our data suggest that both dust (coarse mode aerosol) and smoke (fine mode aerosol) contribute to the precipitation suppression. However, the dust effect is evident over the Gulf of Guinea while the smoke effect is evident over both land and ocean. A back trajectory analysis further demonstrates that the precipitation reduction is statistically linked to the upwind aerosol concentration. This study suggests that African aerosol outbreaks in the WAM region can influence precipitation in the local monsoon system which has direct societal impact on the local community. It calls for more systematic investigations to determine the modulating mechanisms using both observational and modeling approaches.

We used the OMEGA imaging spectrometer aboard Mars Express to study the evolution of the water vapor abundance over the Hellas basin, as a function of the seasonal cycle. The H 2 O column density is found to range from very low values (between southern fall and winter) up to more than 15 pr-µm during southern spring and summer. The general behavior is consistent with the expected seasonal cycle of water vapor on Mars, as previously observed by TES and modeled. In particular, the maximum water vapor content is observed around the southern solstice, and is significantly less than its northern couterpart. However, there is a noticeable discrepancy around the northern spring equinox (L s = 330-60 • ), where the observed H 2 O column densities are significantly lower than the values predicted by the GCM. Our data show an abrupt enhancement of the water vapor column density (from 3 to 16 pr-µm) on a timescale of 3 days, for L s = 251-254 • . Such an increase, not predicted by the GCM, was also occasionally observed by TES over Hellas during previous martian years at the same season; however, its origin remains to be understood.

Accurate estimates of surface energy exchange components are critical for understanding many physical processes of large lakes and their atmospheric environment. In this paper, the seasonal cycle of latent, sensible, and total heat flux from the surface of the Great Lakes is estimated. Lake surface temperatures derived from the NOAA/AVHRR satellite, along with meteorological data from surface station observations are incorporated in order to estimate spatial distributions of fluxes. Several well-known features are evident. Among these are the very high outgoing fluxes of latent and sensible heat during the late fall and early winter, which drive strong cooling of the lake surface and consequent convective mixing within the lake column. Another is greater seasonal variation of surface temperature and fluxes in shallower waters than in deeper waters. Due to strong static stability of the overlying atmospheric boundary layer during the spring, both the magnitude and the spatial variations of latent and sensible heat fluxes are small during the spring and, to a lesser degree, during the summer. The annual cycles of latent and sensible heat flux over the Great Lakes are roughly opposite in phase to the same fluxes over land, indicating a large exchange of energy via atmospheric advection between the lake and land surfaces. A major weakness of the method used here is that heat fluxes are calculated on the basis of an icefree surface, making the derived fluxes for January through March roughly estimated.

Saturn's satellite Titan is a particularly interesting body in our solar system. It is the only satellite with a dense atmosphere, which is primarily made of nitrogen and methane. It harbours an intricate photochemistry, that populates the atmosphere with aerosols, but that should deplete irreversibly the methane. The observation that methane is not depleted led to the study of Titan's methane cycle, starting with its atmospheric part. The features that inhabit Titan's atmosphere can last for timescales varying from year to day. For instance, the reversal of the north-south asymmetry is linked to the 16-year seasonal cycle. Diurnal phenomena have also been observed, like a stratospheric haze enhancement or a possible tropospheric drizzle. Furthermore, clouds have been reported on Titan since 1993. From these first detections and up to now, with the recent inputs from the Cassini-Huygens mission, clouds have displayed a large range of shapes, altitudes, and natures, from the flocky tropospheric clouds at the south pole to the stratiform ones in the northern stratosphere. It is still difficult to compose a clear picture of the physical processes governing these phenomena, even M. Hirtzig (B)

Dry Valleys of southern Victoria Land, Antarctica. In contrast to tcmperatc lakes that have diurnal photic periods, antarctic (and arctic) lakes have a yearly photic period. An unusual feature of the antarctic lakes is the occurrence of 0, at supersaturated levels in certain portions of the water column. Here we report the first sediment 0, profiles obtained using a microelectrode from a perennially ice-covered antarctic lake. Sediment cores collected in January and October 1987 from Lake Hoare in Taylor Valley show oxygenation down to 15, and in some cases, 25 cm. The oxygenation of sediments several centimeters below the sediment-water interface is atypical for lake sediments and may be characteristic of perennially ice-covered lakes. There is a significant difference between the observed January and October sediment 0, profiles. Several explanations may account for the difference, including seasonality. A time-dependent model is presented which tests the feasibility of a seasonal cycle resulting from the long photopcriod and benthic primary production in sediments overlain by a highly oxygenated water column.

En este artículo, se identifican determinantes de la oferta primaria de ganado vacuno para cebar en el departamento de Córdoba, Colombia, durante el período 2007-2018. Para ello se utiliza un modelo econométrico lineal autorregresivo con retardos distribuidos que permite, mediante la prueba límite, establecer las relaciones de largo y de corto plazo entre las variables. Los resultados empíricos evidencian que los ganaderos responden a estímulos de mercado, como precios y costos de producción; son adversos al riesgo-clima y al riego-precio; compiten por recursos productivos con un cultivo como el maíz; la predominancia del sistema de producción del doble propósito y la presencia de comercializadores intermediarios que realizan ceba incompleta explican una relación directa entre el ciclo de la ceba final y la oferta primaria. 

In 2003, strong energetic particle precipitation (EPP) events occurred producing massive amounts of ionization which affected the polar region significantly perturbing its chemical state down to the middle stratosphere. These events and their effects are generally left unaccounted for in current models of stratospheric chemistry and large differences between observations and models are then noted. In this study, we use a coupled 3-D stratospheric dynamicalchemical model and assimilation system to ingest MIPAS temperature and chemical observations. The goal is to gain further understanding of assimilation and monitoring processes during EPP events and their impacts on the stratospheric polar chemistry. Moreover, we investigate the feasibility of assimilating valid "outlier" observations associated with such events. We use OmF (Observation minus Forecast) residuals as they filter out phenomena well reproduced by the model (such as gas phase chemistry, transport, diurnal and seasonal cycles) thus revealing a clear trace of the EPP. Inspection of OmF statistics in both passive (without chemical assimilation) and active (with chemical assimilation) cases altogether provides a powerful diagnostic tool to assess the model and assimilation system. We also show that passive OmF can permit a satisfactory evaluation of the ozone partial column loss due to EPP effects. Results suggest a small but significant loss of 5-6 DU (Dobson Units) during an EPP-IE

limate models used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) on the whole reproduce the observed seasonal cycle and 20th century warming trend of 0.8°C (1.5°F) in the Pacific Northwest, and point to much greater warming for the next century. These models project increases in annual temperature of, on average, 1.1°C (2.0°F) by the 2020s, 1.8°C (3.2°F) by the 2040s, and 3.0°C (5.3°F) by the 2080s, compared with the average from 1970 to 1999, averaged across all climate models. Rates of warming range from 0.1 to 0.6°C (0.2° to 1.0°F) per decade. Projected changes in annual precipitation, averaged over all models, are small (+1 to +2%), but some models project an enhanced seasonal cycle with changes toward wetter autumns and winters and drier summers. Changes in nearshore sea surface temperatures, though smaller than on land, are likely to substantially exceed interannual variability, but coastal upwelling changes little. Rates of 21 st century sea level rise will depend on poorly known factors like ice sheet instability in Greenland and Antarctica, and could be as low as 20th century values (20cm, 8") or as large as 1.3m (50").

limate models used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) on the whole reproduce the observed seasonal cycle and 20th century warming trend of 0.8°C (1.5°F) in the Pacific Northwest, and point to much greater warming for the next century. These models project increases in annual temperature of, on average, 1.1°C (2.0°F) by the 2020s, 1.8°C (3.2°F) by the 2040s, and 3.0°C (5.3°F) by the 2080s, compared with the average from 1970 to 1999, averaged across all climate models. Rates of warming range from 0.1 to 0.6°C (0.2° to 1.0°F) per decade. Projected changes in annual precipitation, averaged over all models, are small (+1 to +2%), but some models project an enhanced seasonal cycle with changes toward wetter autumns and winters and drier summers. Changes in nearshore sea surface temperatures, though smaller than on land, are likely to substantially exceed interannual variability, but coastal upwelling changes little. Rates of 21 st century sea level rise will depend on poorly known factors like ice sheet instability in Greenland and Antarctica, and could be as low as 20th century values (20cm, 8") or as large as 1.3m (50").

Sea surface temperature (SST) data and two different upper-ocean temperature analyses are used to study the winter-to-winter recurrence of SST anomalies in the North Pacific Ocean. The SSTs recur when temperature anomalies that form in the deep ocean mixed layer in late winter/early spring are isolated from the atmosphere in the summer seasonal thermocline and then reemerge at the surface when the mixed layer deepens during the following fall/winter. This ''reemergence mechanism'' is evaluated over the basin by correlating the time series of the leading pattern of ocean temperature anomalies in the summer seasonal thermocline (ϳ60-85 m in August-September) with SST anomalies over the course of the year. The results indicate that the dominant large-scale SST anomaly pattern that forms in the North Pacific during late winter, with anomalies of one sign in the central Pacific and the opposite sign along the coast of North America, is sequestered in the seasonal thermocline in summer and returns to the surface in the following fall, with little persistence at the surface in summer. Regions in the east, central, and west Pacific all show signs of the reemergence process but indicate that it is influenced by the timing and amplitude of the mean seasonal cycle in mixed layer depth. The maximum mixed layer depth increases from east to west across the basin: as a result, the thermal anomalies are shallower and return to the surface sooner in the east compared with the west Pacific. At some locations, the reemerging signal is also influenced by when the SST anomalies are created. In the east Pacific, SST anomalies that are initiated in February-March extend through a deeper mixed layer, persist at greater depths in summer, and are then reentrained later in the year compared with those initiated in April-May.

We present an analysis of the seasonal cycle of the last 50 years of records of surface temperature in Italy, as described by observations of maximum and minimum daily temperature, and of the surface and upper air temperature of the whole Mediterranean area, as described by the 1951-2000 NCEP reanalysis. We compute the best estimate of the seasonal cycle of the variables considered by adopting the cyclograms' technique. In the case of the Italian surface temperature, we observe that in general the minimum temperature cycle lags behind the maximum temperature cycle, and that the cycles of the Southern Italy temperatures records lag behind the corresponding cycles referring to Northern Italy. In the case of the NCEP reanalysis data for the whole Mediterranean area, we observe that at surface the phase and amplitude of the seasonal cycle are strongly characterized by the signature of the underlying surface, while in the upper air large-scale features related to ocean-continent contrast come into play. All seasonal cycles lag considerably behind the solar cycle. In all cases considered, the amplitude and phase of the seasonal cycles do not show any statistically significant trend in the time interval considered. This works supports the idea that climate change studies are much more reliable when upper air data are taken into account.

NASA Langley Research Center NOAA Climate Data Record Program Calibration FCDR Specifications • Gains produced monthly using 5 methods Desert, Polar snow invariant targets (IT) Deep convective clouds (DCC) Simultaneous Nadir Overpass (SNO) w/ Aqua MODIS Merged DCC & IT results • Monthly mean gains, g, 1978-2012 • Polynomial fits to monthly means, fn(dsl) m = m0 + m1•dsl + m2•dsl Inputs to Calibration FCDR • Re-navigated Advanced Very High Resolution Radiometer (AVHRR) 0.63, 0.86, and 1.6-μm brightness counts, C • Observational geometric conditions, date • Invariant site reflectance models, SBAFs • DCC BRDF models • Spectral solar constant, launch date, Co

We tested hypotheses about how estuarine fish assemblages respond to habitat degradation and then integrated these responses into an overall index, the Estuarine Biotic Integrity Index (EBI), which smnmarized observed changes. Fish assemblages (based on trawl catches) and habitat quality were measured monthly or biweekly at nine sites in two estuaries from March 1988 to June 1990. Submerged aquatic vegetation habitats were classified as low or medium quality based on year-round measurements of chemical and physical characteristics (phytoplankton blooms; macroalgae; dissolved oxygen; nutrients; dredged channels). We tested 15 metrics and selected 8 for inclusion in the EBI: total number of species, dominance, fish abundance (number or biomass), number of nursery species, number of estuarine spawning species, number of resident species, proportion of benthlc-associated fishes, and proportion abnormal or diseased. Fish assemblages in low-quality sites had lower number of species, density, biomass, and dominance compared with mediumquality sites. Fish abundance peaked in July and August, and was lowest in January to March. The seasonal cycle in lowquality sites was damped compared with medium-quality sites. Abundances of fishes using estuaries as a spawning and nursery area and of benthic species were lower in low-quality sites compared to medium-quality sites. The individual metrics and the overall index correlate with habitat degradation. The EBI based on biomass did not do better than the EBI based on number, indicating that the extra effort to obtain biomass may not be warranted. We suggest the EBI is a useful indicator of estuarine ecosystem status because it reflects the relationship between anthropogenic alterations in estuarine ecosystems and the status of higher trophic levels.

To study the spatial and temporal variability of tropospheric ozone in the marine boundary layer over the Aegean Sea (eastern Mediterranean), an O 3 analyzer has been installed onboard of a passenger vessel traveling on a regular basis in the Aegean Sea (from Heraklion/Crete 35°30 0 N, 25°13 0 E to Thessaloniki 40°64 0 N, 22°97 0 E) during a period of 14 months (August 1999 to November 2000). In addition, O 3 data have been obtained on a daily basis at the regional background station of Finokalia (Crete; 35°30 0 N, 25°70 0 E) since September 1997, short-term measurements of O 3 were performed over Crete during the PAUR II campaign (May 1999), and the first O 3 data from a rural area (40°32 0 N, 23°50 0 E) close to Thessaloniki at the north of Greece have been collected from March 2000 to January 2001. This survey extensive points out the existence of a welldefined seasonal cycle in boundary layer O 3 with maximum in summer both above the Aegean Sea and at Finokalia. However, the seasonal signal (defined as the summer/winter ratio) is not constant and varies as a function of air mass origin from 1.33 to 1.15 for the N-NE and SW-S sectors, respectively, in line with the geographical location of the O 3 precursor sources. Our data show the absence of any significant longitudinal gradient over Crete at least during spring and autumn and the absence of significant latitudinal gradient between the north and south Aegean Sea during all seasons for air masses having similar origin. The above results indicate that long-range transport is the main factor accounting for the elevated O 3 levels above the eastern Mediterranean Sea. Thus (1) O 3 data from Finokalia, where the longest time series are available for the area, have regional significance and (2) over the entire Aegean basin, ozone values are above the 32 ppbv European Union (EU) phytotoxicity limit throughout the year and above the 53 ppbv EU health protection limit most of the time during the dry season of the year. The very significant correlation between black carbon (BC) and O 3 observed during an intensive campaign in May 2000 provides an indication that the high O 3 concentrations at Finokalia resulted from ageing of air masses strongly affected by combustion processes.

The first year‐round observations of seasonal and diurnal variations of background ozone at a coastal site on Crete Island in the southeast Mediterranean area are presented here. They point out (1) the existence of a well‐defined seasonal cycle with maximum during summer months, (2) the presence of elevated O3 levels (up to 80 ppbv) during daytime and over time periods of several days, and (3) the dependence of O3 mixing ratios on air mass origin. Comparison with three‐dimensional chemistry transport model results shows that during summer the measured O3 values exceed the calculated by 10–20 ppbv. Inclusion of biomass burning and biogenic volatile organic emissions in the model could partly offset the discrepancy between model results and observations.

We synthesised observations of total particle number (CN) concentration from 36 sites around the world. We found that annual mean CN concentrations are typically 300-2000 cm -3 in the marine boundary layer and free troposphere (FT) and 1000-10 000 cm -3 in the continental boundary layer (BL). Many sites exhibit pronounced seasonality with summer time concentrations a factor of 2-10 greater than wintertime concentrations. We used these CN obser-