Madden Julian Oscillation

Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia. Department of Geophysics, University of Chile, Santiago, Chile. Millennium Nucleus on Paleoclimate of the Southern Hemisphere. Monash Weather and Climate, Monash University, Melbourne, Australia. Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark. ∗Email: Steven.Phipps@utas.edu.au

Air–Sea Interactions in the Northern Indian Ocean (ASIRI) is an international research effort (2013–17) aimed at understanding and quantifying coupled atmosphere–ocean dynamics of the Bay of Bengal (BoB) with relevance to Indian Ocean monsoons. Working collaboratively, more than 20 research institutions are acquiring field observations coupled with operational and high-resolution models to address scientific issues that have stymied the monsoon predictability. ASIRI combines new and mature observational technologies to resolve submesoscale to regional-scale currents and hydrophysical fields. These data reveal BoB’s sharp frontal features, submesoscale variability, low-salinity lenses and filaments, and shallow mixed layers, with relatively weak turbulent mixing. Observed physical features include energetic high-frequency internal waves in the southern BoB, energetic mesoscale and submesoscale features including an intrathermocline eddy in the central BoB, and a high-resolution view ...

The fourth version of the Community Climate System Model (CCSM4) was recently completed and released to the climate community. This paper describes developments to all CCSM components, and documents fully coupled preindustrial control runs compared to the previous version, CCSM3. Using the standard atmosphere and land resolution of 1° results in the sea surface temperature biases in the major upwelling regions being comparable to the 1.4°-resolution CCSM3. Two changes to the deep convection scheme in the atmosphere component result in CCSM4 producing El Niño–Southern Oscillation variability with a much more realistic frequency distribution than in CCSM3, although the amplitude is too large compared to observations. These changes also improve the Madden–Julian oscillation and the frequency distribution of tropical precipitation. A new overflow parameterization in the ocean component leads to an improved simulation of the Gulf Stream path and the North Atlantic Ocean meridional overtu...

Quasi-biennial oscillations (QBOs) in thirteen atmospheric general circulation models forced with both observed and annually repeating sea surface temperatures (SSTs) are evaluated. In most models the QBO period is close to, but shorter than, the observed period of 28 months. Amplitudes are within ±20% of the observed QBO amplitude at 10 hPa, but typically about half of that observed at lower altitudes (50 and 70 hPa). For almost all models, the oscillation's amplitude profile shows an overall upward shift compared to reanalysis and its meridional extent is too narrow. Asymmetry in the duration of eastward and westward phases is reasonably well captured, though not all models replicate the observed slowing of the descending westward shear. Westward phases are generally too weak, and most models have an eastward time mean wind bias throughout the depth of the QBO. The intercycle period variability is realistic and in some models is enhanced in the experiment with observed SSTs compared to the experiment with repeated annual cycle SSTs. Mean periods are also sensitive to this difference between SSTs, but only when parametrized non-orographic gravity wave (NOGW) sources are coupled to tropospheric parameters and not prescribed with a fixed value. Overall, however, modelled QBOs are very similar whether or not the prescribed SSTs vary interannually. A portrait of the overall ensemble performance is provided by a normalized grading of QBO metrics. To simulate a QBO, all but one model used parametrized NOGWs, which provided the majority of the total wave forcing at altitudes above 70 hPa in most models.

El principal objetivo de este trabajo es describir detalladamente el comienzo del Monzón Sudamericano utilizando datos de precipitación disponibles en la zona tropical y subtropical de Sudamérica. El análisis fue comparado con el realizado utilizando datos de radiación saliente de onda larga (OLR), con el fin de evaluar la eficiencia de los datos de lluvia para detectar los principales patrones de la evolución del monzón durante la primavera austral. Los resultados muestran que tanto la OLR como la precipitación describen bien el desplazamiento de la convección desde el noroeste hacia el sudeste en el centro de Brasil a principios de octubre. La comparación de diferentes metodologías para establecer fechas de comienzo de la estación lluviosa muestran que el método de , basado en la evolución de OLR, indica el comienzo del monzón en casi toda Sudamérica sin necesitar adaptación para cada región, tal como ocurre con los métodos basados en la precipitación. Los campos medios muestran que la lluvia en Brasil central comienza y se incrementa moderadamente, manteniéndose con valores menores a los observados en el noroeste y sudeste de la región tropical. Posteriormente, un abrupto cambio en la magnitud de la precipitación tiene lugar, en promedio tres péntadas después del inicio de la estación lluviosa, en Brasil central aunque similares cambios se observan en toda la región tropical. Se sugiere que la actividad de los transientes, que ocurre en el comienzo de la estación de lluvia cuando la inestabilidad aumenta y se aproximan las condiciones de verano, es uno de los factores que inciden en el desarrollo de este cambio abrupto en la precipitación. La caracterización de los incrementos en la lluvia provee información complementaria que puede ser utilizada adicionalmente a la fecha de inicio de la misma.

Intensity of precipitation in Indonesia is influenced by convection and propagation of southwest wind. Objective of this study is to analyze the relationship between cold surge and the phenomenon of intra-seasonal climate variability Madden-julian Oscillation (MJO) for affecting precipitation in Indonesia. The data used for identifying the occurrence of cold surge are meridional wind speed data from the ERA-Interim. In addition, this study also used RMM1 and RMM2 index data from Bureau of Meteorology (BOM) for identifying MJO events. The results showed that during East Asian Winter Monsoon (EAWM) in 15 years (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015), there are 362 cold surge events, 186 MJO events, and 113 cold surge events were associated with MJO events. The spread of cold surge can penetrate to equator and brought mass of water vapor that causes dominant precipitation in the Indonesian Sea up to 50-75% from climatological precipitation during EAWM. The MJO convection activity that moves from west to east also increases precipitation, but the distribution of rainfall is wider than cold surge, especially in Eastern Indonesia. MJO and cold surge simultaneously can increase rainfall over 100-150% in any Indonesian region that affected by MJO and cold surge events. The mechanism of heavy rainfall is illustrated by high activity of moisture transport in areas such as Java Sea and coastal areas of Indonesia.

Climate simulations performed with general circulation models (GCMs) are widely viewed as the principal scientific basis for proposed policies to address potential future global climate change. In order to reduce uncertainties in these GCM projections of future climate, there ...

Carbon dioxide (CO 2 ) is the most important anthropogenic greenhouse gas in the present-day climate. Most of the community focuses on its long-term (decadal to centennial) behaviors that are relevant to climate change, but there are relatively few discussions of its higher-frequency forms of variability, and none regarding its subseasonal distribution. In this work, we report a largescale intraseasonal variation in the Atmospheric Infrared Sounder CO 2 data in the global tropical region associated with the Madden-Julian oscillation (MJO). The peak-to-peak amplitude of the composite MJO modulation is ∼1 ppmv, with a standard error of the composite mean <0.1 ppmv. The correlation structure between CO 2 and rainfall and vertical velocity indicate positive (negative) anomalies in CO 2 arise due to upward (downward) large-scale vertical motions in the lower troposphere associated with the MJO. These findings can help elucidate how faster processes can organize, transport, and mix CO 2 and provide a robustness test for coupled carbon-climate models.

Previous studies using satellite measurements showed evidence that subtropical upper troposphere/lower stratosphere ozone (O 3 ) can be modulated by tropical intraseasonal variability, the most dominant form of which is the Madden Julian Oscillation (MJO) with a period of 30-60 days. Here we further study the MJO modulation in the upper troposphere/lower stratosphere O 3 over the northern extratropics and the Arctic. Significant MJO-related O 3 signals (13-20 Dobson units) are found over the northern extratropics (north of 30 N). The O 3 anomalies change their magnitude and patterns depending on the phase of the MJO. Over the Arctic, the MJO-related O 3 anomalies are dominated by a wave number 2 structure and are anticorrelated with the geopotential height (GPH) anomalies at 250 hPa. The latter is similar to the findings in the previous studies over subtropics and indicates that the Arctic upper troposphere/lower stratosphere O 3 anomalies are associated with dynamical motions near the tropopause. The teleconnection from the tropics to the Arctic is likely through propagation of planetary waves generated by the equatorial heating that affects the tropopause height and O 3 at high latitudes.

The large-scale vertical moist thermodynamic structure of the Madden–Julian oscillation (MJO) was documented using the first 2.5 yr (2002–05) of version 4 atmospheric specific humidity and temperature profiles from the Atmospheric Infrared Sounder (AIRS). In this study, this issue is further examined using currently available 7-yr version 5 AIRS data (2002–09) to test its dependence on the AIRS data record lengths, AIRS retrieval versions, and MJO event selection and compositing methods employed. The results indicate a strong consistency of the large-scale vertical moist thermodynamic structure of the MJO between different AIRS data record lengths (2.5 vs 7 yr), different AIRS retrieval versions (4 vs 5), and different MJO analysis methods [the extended empirical orthogonal function (EEOF) method vs the multivariate empirical orthogonal function (MEOF) method]. The large-scale vertical moist thermodynamic structures of the MJO between the AIRS retrievals and the ECMWF Interim Re-Ana...

The atmospheric moisture and temperature profiles from the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit on the NASA Aqua mission, in combination with the precipitation from the Tropical Rainfall Measuring Mission (TRMM), are employed to study the vertical moist thermodynamic structure and spatial–temporal evolution of the Madden–Julian oscillation (MJO). The AIRS data indicate that, in the Indian Ocean and western Pacific, the temperature anomaly exhibits a trimodal vertical structure: a warm (cold) anomaly in the free troposphere (800–250 hPa) and a cold (warm) anomaly near the tropopause (above 250 hPa) and in the lower troposphere (below 800 hPa) associated with enhanced (suppressed) convection. The AIRS moisture anomaly also shows markedly different vertical structures as a function of longitude and the strength of convection anomaly. Most significantly, the AIRS data demonstrate that, over the Indian Ocean and western Pacific, the enhanced (suppressed) c...

We investigate the modulation of aerosols by the Madden-Julian Oscillation (MJO) using multiple, global satellite aerosol products: aerosol index (AI) from the Total Ozone Mapping Spectrometer (TOMS) on Nimbus-7, and aerosol optical thickness (AOT) from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua and the Advanced Very High Resolution Radiometer (AVHRR) on NOAA satellites. A composite MJO analysis indicates that large variations in the TOMS AI and MODIS/AVHRR AOT are found over the equatorial Indian and western Pacific Oceans where MJO convection is active, as well as the tropical Africa and Atlantic Ocean where MJO convection is weak but the background aerosol level is high. A strong inverse linear relationship between the TOMS AI and rainfall anomalies, but a weaker, less coherent positive correlation between the MODIS/AVHRR AOT and rainfall anomalies, were found. The MODIS/AVHRR pattern is consistent with ground-based Aerosol Robotic Network data. These results indicate that the MJO and its associated cloudiness, rainfall, and circulation variability systematically influence the variability in remote sensing aerosol retrieval results. Several physical and retrieval algorithmic factors that may contribute to the observed aerosol-rainfall relationships are discussed. Preliminary analysis indicates that cloud contamination in the aerosol retrievals is likely to be a major contributor to the observed relationships, although we cannot exclude possible contributions from other physical mechanisms. Future research is needed to fully understand these complex aerosol-rainfall relationships.

We investigate the intraseasonal (30–90 day) variations in satellite‐observed tropical total ozone (O3) and their connection to the Madden‐Julian Oscillation (MJO). Tropical total O3 intraseasonal variations are large (∼±10 DU) and comparable to those in annual and interannual time scales. These O3 anomalies are mainly evident in the subtropics over the Pacific and eastern; hemisphere and propagate slowly eastward (∼5 m s−1). The subtropical negative (positive) O3 anomalies are typically collocated with the subtropical upper troposphere anticyclones (cyclones) generated by equatorial MJO convection and flank or lie to the west of the equatorial enhanced (suppressed) MJO convection. The subtropical O3 are anti‐correlated with geopotential height anomalies near the tropopause and thus mainly associated with the O3 variability in the stratosphere rather the troposphere. Over the equatorial regions, total O3 anomalies are small.

representation of the NAO and the utility of this approach. Finally, we note that the interannual statistics of the NAO and associated surface climate impacts are subject to uncertainty due to sampling fluctuations, even when based on a century of data.

Existing numerical models produce large error in simulating the Madden–Julian oscillation (MJO), thereby underestimating its predictability. In this paper, the predictability limit of the MJO is determined by the nonlinear local Lyapunov exponent approach, which provides an estimate of atmospheric predictability based on the observational data. The results show that the predictability limit of the MJO obtained from the bandpass-filtered (30–80 days) outgoing longwave radiation and wind fields, which serves as an empirical estimate of the theoretical potential predictability of the MJO, can exceed 5 weeks, which is well above the 1-week predictability of background noise caused by bandpass filtering. In contrast, a real-time analysis of MJO predictability using the real-time multivariate MJO (RMM) index, as introduced by Wheeler and Hendon, reveals a predictability limit of about 3 weeks. The findings reported here raise the possibility of obtaining a higher predictability limit in r...

The predictive performance of the Madden-Julian Oscillation (MJO) in the National Centers for Environmental Prediction's (NCEP's) operational coupled, Climate Forecast System (CFS) model is assessed and statisticaldynamical hybrid models are developed based on this numerical model to improve forecasting skill. By projecting ENSO-removed variables onto the principal patterns of the MJO convection and upper-and lower-level circulations, MJO-related signals in the dynamical model forecasts are extracted. It is found that the coupled model exhibits useful predictability out to 2 and 3 pentads when the initial MJO convection is located over the Maritime Continent and the Indian Ocean, respectively. The first hybrid model (HYBRID1) developed is a lagged multiple linear regression scheme, where the previous values of the first two leading principal components (PCs) from the coupled model are used as predictors along with the latest observed PC values. The other hybrid model (HYBRID2) is constructed to fit the predicted PC time series from the coupled model to the observed PCs at each lead time using 13 years of training data fields. HYBRID2 does not produce persistent improvement in forecast skill compared to CFS, whereas for HYBRID1, the resulting correlation coefficient and root mean square (RMS) skills are considerably enhanced due to the incorporation of lagged correlation information between the two PCs. The skill improvement of HYBRID1 ranges from 15 to 50% relative to the CFS forecast and the improvement in the correlation skill is greater than the RMS error correction. When the MJO convection is located initially over the Maritime Continent during the northern summer, the CFS forecast skill is as small as the persistence forecast, whereas HYBRID1 demonstrates the greatest skill improvement. During ENSO winters, the forecast skill is enhanced by ∼30% by HYBRID1. In particular, the skill improvement in La Niña years is noticeably greater than in El Niño years.

The combined effect of the Madden-Julian oscillation (MJO) and Arctic oscillation (AO) on the temperature variation over Asia is investigated using the thermodynamic budget equation. Because of the distinct geographical origin of the two atmospheric modes, the influence of AO is more dominant in the higher latitude, whereas the MJO impact is more predominant in the lower latitude. Hence, the physical process responsible for the surface cold anomaly is different for northern and southern Asia. Cold anomaly appears in most of Asia 20-25 days after the MJO phase 6 (corresponding to the phase 2-3). However, more strengthened cold anomaly occurs over northern Asia under the negative AO state and it is caused by advection of temperature anomaly by climatological northerly wind associated with the East Asia winter monsoon flow. On the other hand, much stronger cold anomaly is seen over southern Asia under the positive AO state for the same lag day of the initial MJO phase 6. Aside from the upward overturning circulation forced by the tropical MJO over the subtropics and lower midlatitudes, the weakening of the East Asia subtropical jet by the positive AO induces additional upward motion over southern Asia to adjust the thermal wind balance. The combined effect of the MJO and AO also influences on the occurrence of extreme cold event. Under the negative (positive) AO phase, the extreme cold event occurrence probability over northern (southern) Asia increases by 90% (60%) compared to that for all winter days. The relative increase rate for the MJO phases 2-3 is ~30% over southern Asia. The cold event occurrence probability for the combined modes is about the twice that for only MJO impact, suggesting that an incorporation of both modes enhance the predictability of extreme cold event.

This study doc u ments a de tailed anal y sis on the Mad den-Julian Os cil la tion (MJO) sim u lated by the Na tional Cen ters for En vi ron men tal Pre dic tion (NCEP) us ing the Global Fore cast Sys tem (GFS) model ver sion 2003 cou pled with the Cli mate Fore cast Sys tem model (CFS) con sist ing of the 2003 ver sion of GFS and the Geo phys i cal Fluid Dy nam ics Lab o ra tory (GFDL) Mod u lar Ocean Model V.3 (MOM3). The anal y ses are based upon a 21-year sim u la tion of AMIP-type with GFS and CMIP-type with CFS. It is found that air-sea cou pling in CFS is shown to im prove the co her ence be tween con vec tion and large-scale cir cu la tion as so ci ated with the MJO. The too fast prop a ga tion of con vec tion from the In dian Ocean to the mar i time con ti nents and the west ern Pa cific in GFS is im proved (slowed down) in CFS. Both GFS and CFS pro duce too strong intraseasonal con vec tive heat ing and cir cu la tion anom a lies in the cen tral-east ern Pa cific; fur ther, the air-sea cou pling in CFS en hances this un re al is tic fea ture. The sim u lated mean slow phase speed of east ward prop a gat ing low-wavenumber com po nents shown in the wavenumber-fre quency spec tra is due to the slow prop a ga tion in the cen tral-east ern Pa cific in both GFS and CFS. Er rors in model cli ma tol ogy may have some ef fect upon the sim u lated MJO and two pos si ble in flu ences are: (i) CFS fails to sim u late the wes ter lies over mar i time con ti nents and west ern Pa cific ar eas, re sult ing in an un re al is tic rep re sen ta tion of sur face la tent heat flux as so ci ated with the MJO; and (ii) ver ti cal east erly wind shear from the In dian Ocean to the west ern Pacific in CFS is much weaker than that in the observation and in GFS, which may adversely affect the eastward propagation of the simulated MJO.

This study investigates the capability for simulating the Madden–Julian oscillation (MJO) in a series of atmosphere–ocean coupled and uncoupled simulations using NCEP operational general circulation models. The effect of air–sea coupling on the MJO is examined by comparing long-term simulations from the coupled Climate Forecast System (CFS T62) and the atmospheric Global Forecast System (GFS T62) models. Another coupled simulation with a higher horizontal resolution model (CFS T126) is performed to investigate the impact of model horizontal resolution. Furthermore, to examine the impact on a deep convection scheme, an additional coupled T126 run (CFS T126RAS) is conducted with the relaxed Arakawa–Schubert (RAS) scheme. The most important factors for the proper simulation of the MJO are investigated from these runs. The empirical orthogonal function, lagged regression, and spectral analyses indicated that the interactive air–sea coupling greatly improved the coherence between convect...

Observational studies are presented on the relationship between El Nin ˜o-Southern Oscillation (ENSO) and the northward propagating intraseasonal oscillation (NPISO) in the east Asian summer monsoon (EASM) system. The summer NPISO activity shows a significant correlation with the preceding winter extreme phase of ENSO cycles. A higher correlation appears during late summer, which is consistent with frequent heavy rainfall events at that time as revealed in some previous case studies. The westward expansion of broad anticyclonic circulation over the western North Pacific and the smaller cyclonic circulation around Korea and Japan are found to be associated with the NPISO activity. ENSO affects the late summer NPISO activity through an atmospheric bridge and wave propagation; the springtime Indian Ocean sea surface temperature warming induced by ENSO through the Walker circulation leads to the downward motion and suppressed convection over the Philippine Sea, and this generates the forced Rossby wave train, forming the above south-to-north low-level circulation anomalies.

The primary aim of this study is to understand the heavy precipitation events over Oceanic regions using vector wind retrievals from space based scatterometers in combination with precipitation products from satellite and model reanalysis products. Heavy precipitation over oceans is a less understood phenomenon and this study tries to fill in the gaps which may lead us to a better understanding of heavy precipitation over oceans. Various phenomenon may lead to intense precipitation viz. MJO (Madden-Julian Oscillation), Extratropical cyclones, MCSs (Mesoscale Convective Systems), that occur inside or outside the tropics and if we can decipher the physical mechanisms behind occurrence of heavy precipitation, then it may lead us to a better understanding of such events which further may help us in building more robust weather and climate models. During a heavy precipitation event, scatterometer wind observations may lead us to understand the governing dynamics behind that event near th...

Melbourne, Australia, experienced a large increase in its maximum daily temperature on 7 February 2009. This new record was set after an extended period of drought. We test whether droughts tend to lead to increased daily maximum temperatures in Melbourne, relative to temperatures experienced after wet periods, separating this drought effect from the effect of synoptic-scale wind-flow on maximum temperatures. Data from 1957-2008 indicate that the daily maximum temperature is typically 1-3 °C higher after drought, relative to a similar synoptic situation after a wet period, in situations typically associated with high maximum temperatures (i.e. with winds from the north). When the wind is from the south (i.e. from over the sea) there is typically little or no difference between daily maximum temperatures after droughts or wet periods.

Melbourne, Australia, experienced a large increase in its maximum daily temperature on 7 February 2009. This new record was set after an extended period of drought. We test whether droughts tend to lead to increased daily maximum temperatures in Melbourne, relative to temperatures experienced after wet periods, separating this drought effect from the effect of synoptic-scale wind-flow on maximum temperatures. Data from 1957-2008 indicate that the daily maximum temperature is typically 1-3 °C higher after drought, relative to a similar synoptic situation after a wet period, in situations typically associated with high maximum temperatures (i.e. with winds from the north). When the wind is from the south (i.e. from over the sea) there is typically little or no difference between daily maximum temperatures after droughts or wet periods.

West Kalimantan has experienced significant loss of wet primary forests in recent years. During 2017-2021, the region also faced considerable forest and land fires compared to other areas in Kalimantan. Factors such as low rainfall and prolonged drought have contributed to the occurrence of forest fire. This research was conducted using daily rainfall data at 127 observation points and hotspot data during 2012 to 2021. The research results show monthly CDD characteristics in West Kalimantan, with the highest number of CDD occurring in Kubu Raya Regency for 126 days and the lowest in Kayong Utara, Melawi, Kubu Raya, Sambas, Kapuas Hulu, Bengkayang, Mempawah, Sintang, and Pontianak City for 3 days. The hotspot distribution pattern indicates the highest number of hotspots occurring in August throughout the 10-year period. Hotspots probability varies for each CDD category: very short CDD has a probability ranging from 0.01 to 0.11, short CDD has a probability ranging from 0.03 to 0.33, moderate CDD has a probability ranging from 0.03 to 0.38, long CDD has a probability ranging from 0.00 to 0.53, very long CDD has a probability ranging from 0.00 to 0.43, and extremely long CDD has a probability ranging from 0.10 to 0.48.

Tropical rainforests are known to exhibit low intrasea-8 sonal precipitation variability compared with oceanic areas 9 with similar mean precipitation in observations and models. 10 In the present study, the potential role of transpiration for 11 this difference in precipitation variability is investigated 12 using the National Center for Atmospheric Research 13 (NCAR) atmospheric general circulation model. Comparing 14 model results with and without transpiration shows that in 15 the absence of transpiration, mean precipitation decreases as 16 may be expected. However the incidence of both higher 17 daily total column water and more intense precipitation 18 increases without transpiration; consequently the variability 19 of precipitation increases substantially. These results can be 20 understood in terms of the complex interplay of local near-21 surface and remote moist dynamical processes with both 22 local positive (boundary-layer drying) and large-scale neg-23 ative (increased large-scale convergence) feedbacks when 24 transpiration is disabled in the model. It is also shown that 25 surface turbulent fluxes over tropical rainforests are highly 26 correlated with incoming solar energy but only weakly cor-27 related with wind speed, possibly decoupling land precipi-28 tation from large-scale disturbances like Madden-Julian 29 Oscillation.

The role of an active phase of the Madden-Julian Oscillation (MJO) on the evolution of a mesoscale convective systems (MCS) leading to a tropical depression is investigated in the South-West Indian Ocean during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field experiment, with a numerical limited-area atmospheric model. A mesoscale vortex is followed in the low-troposphere from the initiation of the active MJO phase. It is shown that the interaction of the vortex with the Equatorial jet associated with the MJO plays an important role on the vortex development. As the vortex encounters the southern part of the low-level jet, it undergoes intensification that is explained by the barotropic conversion of kinetic energy from the low-level jet to the vortex.

Atmospheric cold pools generated from convective downdrafts can significantly modulate air-sea interaction processes, though the variability in cold pool events is not yet documented in the Bay of Bengal (BoB). In this study, the seasonal and diurnal variability of cold pool events (defined as a drop in air temperature greater than 1 °C within 30 min) in the BoB is examined using moored buoy measurements with 10-min temporal resolution at 8°N, 12°N, and 15°N along 90°E. The analysis shows that cold pools are plentiful and frequent during summer (May-September) and fall (October-November) compared to winter (December-February) and spring (March-April). Results also indicate a significant diurnal variability at 15°N and 12°N (but not at 8°N) during summer, with more frequent and intense cold pool events in the afternoon. Cold pools lead to an intensification of turbulent heat exchange between the ocean and atmosphere, with increased latent heat loss (~ 80 Wm -2 ) through both an increase in wind speed and reduction in air specific humidity and increased sensible heat loss (~ 40 Wm -2 ) due primarily to air temperature drops. There is also a significant diurnal variability in these air-sea exchanges during the summer, with a twofold enhancement in latent and sensible heat fluxes associated with afternoon vs nighttime cold pools events. Finally, we establish the connection between the enhancement of afternoon cold pool events and southeastward propagating synoptic-scale rainfall activity on diurnal time scales from the western BoB.

The Somali Low Level Jet (SLLJ) is the most important moisture source for India during the monsoon season. A linkage between the moisture uptake over the equatorial area of the SLLJ and the rainfall variability over most of continental India has also been recently indicated. On the other hand, the Madden-Julian Oscillation (MJO) has been identified as a dominant mode of the intraseasonal variability of the Indian summer monsoon rainfall, since the northward propagation of the boreal summer MJO is closely associated with the active and break phases of monsoon rainfall. But a question remains open: is there a relationship between the moisture transport of the SLLJ and the MJO evolution? In this work, a lagrangian approach is used to track the evaporation minus precipitation (E - P) evolution along trajectories of particles initially situated over the equatorial region of SLLJ. The impact of the MJO propagation on the water budget transport of the SLLJ is examined by making composites ...

Southeastern Brazil is the most populated and economically developed region of this country. Its climate consists of two distinct seasons: the dry season, extending from April to September, the precipitation is significantly reduced in comparison to that of the wet season, which extends from October to March. However, during nine days of the 2016 dry season, successive convective systems were associated with atypical precipitation events, tornadoes and at least one microburst over the southern part of this region. These events led to flooding, damages to buildings, shortages of electricity and water in several places, many injuries, and two documented deaths. The present study investigates the synoptic and dynamical features related to these anomalous events. The convective systems were embedded in an unstable environment with intense low-level jet flow and strong wind shear and were supported by a sequence of extratropical cyclones occurring over the Southwest Atlantic Ocean. These...

Spatial fields of outgoing long wave radiation (OLR) spectrum variance of the 1979-2016 austral summer months in southern Brazil are analyzed on different timescales: synoptic, sub-monthly, and intra-seasonal. Variability fields differ both in intensity and location and highlight dominant convection cycles in the study area. The results show that the amplitude of sub-monthly variability is greater than that of the other scales in the southeastern region of Brazil, while the synoptic scale prevails in the southern region. The above-mentioned scales show greater amplitudes over the western Pacific Ocean where the Madden-Julian Oscillation plays an important role, along the South Pacific Convergence Zone, and over the storm track areas over the South Pacific Ocean. The influence of spectral OLR scale interaction is also analyzed, associated to the occurrence of two intense rainfall events over the southeastern Brazil in the austral summers of 2011 and 2014 when the South Atlantic Conve...

The semiannual oscillation (SAO) is observed in circulation changes in the equatorial middle atmosphere, which consist of two separate maxima centered near the stratopause (SSAO) and the upper mesosphere (MSAO) with an approximate out-ofphase relathionship between the two [e.g., Andrews et al., 1987]. The SSAO has eastely and westerly maxima at solstices and equinoxes, respectively, while the MSAO shows an out-of-phase change with the SSAO. It is known that somewhat different consideration must be made between the SSAO and the MSAO for their forcing mechanisms, and it seems to be also true of their interannual changes. In this study, we make global gridpoint data for geopotential and temperature fields up to the mesopause level derived from Aura MLS data, to make dynamical analyses for equatorial zonal wind and temperature changes since August 2004 to present. It is found that the strength of both the SSAO and MSAO might be modulated by stratospheric sudden warming (SSW) events in b...

Indonesia, as a maritime continent, is vulnerable to environmental disasters
such as floods and landslides due to extreme rainfall. This study aims to
identify changes in the influence of ENSO and IOD on extreme rainfall across
Indonesia, specifically during the September-October-November period. We
used rainfall and sea surface temperature data from the CMIP6 climate model
for the historical period (1985-2014), near-future (2031-2060), and far-future
(2061-2090) projections under SSP2-4.5 and SSP 5-8.5 climate scenarios. The
relation between rainfall dan ENSO/IOD was simply defined by linear
regression approach. We analyzed the change of influence by comparing the
historical and the future condition. The results indicated that the changes in
the teleconnection of ENSO and IOD to extreme rainfall in future is
consistently negative, except for Java (near-future) and Kalimantan and
southern Sumatra (far-future). Our finding revealed that significant changes
in the teleconnection varied throughout maritime continent. The maximum
change was found in Northern Kalimantan, which reached values of -80
mm/°C due to ENSO and -180 mm/°C due to IOD for near future. These
findings highlight the spatial variability in teleconnection changes across
Indonesia, underscoring the need for region-specific climate adaptation
measures in response to evolving extreme rainfall patterns.

Mean conditions and interannual variability of austral summer rainfall in southeastern South America are studied in 20 coupled general circulation models (CGCMs) from the WCRP/CMIP3 dataset. Both current-climate conditions and the SRES-A1B climate-change scenario are evaluated. Focus is made in analyzing precipitation changes in the La Plata Basin (LPB) in the subtropics and the South Atlantic Convergence Zone (SACZ), key component of the South American Monsoon System, in the tropics.

The need for early seasonal forecasts stimulates continuous research in climate teleconnections. The large variability of the Mediterranean climate presents a greater difficulty in predicting climate anomalies. This article reviews teleconnection indices commonly used for the Mediterranean basin and explores possible extensions of one of them, the Mediterranean Oscillation index (MOi). In particular, the anomalies of the geopotential height field at 500 hPa are analyzed using segmentation of the Mediterranean basin in seven spatial windows: three at eastern and four at western. That is, different versions of an Upper-Level Mediterranean Oscillation index (ULMOi) were calculated, and monthly and annual variability of precipitation and temperature were analyzed for 53 observatories from 1951 to 2015. Best versions were selected according to the Pearson correlation, its related p-value, and two measures of standardized error. The combination of the Balearic Sea and Libya/Egypt windows was the best for precipitation and temperature, respectively. The ULMOi showed the highest predictive ability in combination with the Atlantic Multidecadal Oscillation index (AMOi) for the annual temperature throughout the Mediterranean basin. The best model built from the indices presented a final mean error between 15% and 25% in annual precipitation for most of the studied area.

The response of the ocean to three Madden-Julian Oscillation (MJO) events during the fall of 2011 is simulated by the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) in a fully coupled mode with high resolution in the atmosphere and ocean. The model simulates the cooler sea surface temperature (SST) and disappearance of the diurnal cycle in SST during the active phase of the MJO and it compares well with the observed SST from Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) buoys. The most striking direct response to the westerly zonal wind stress associated with the onset of the MJO is a rapidly accelerating Yoshida jet in the ocean mixed layer with equatorial zonal currents exceeding 1 m s -1 . These jets are found in the model as well as the RAMA buoy observations. In the model, the Yoshida jet is superimposed on the seasonal Wyrtki jet that has a subsurface local maximum between 50 and 150 m. A shear layer separates the subsurface seasonal jet and the surface jet forced by the MJO. The sea surface elevation response and upper ocean heat content show wind generated westward propagating Rossby waves symmetric around the equator and an associated eastward propagating equatorial Kelvin wave response. After the third MJO event, the Yoshida jet spans most of the equatorial Indian Ocean. Upon reaching the Indonesian coast, the associated equatorial Kelvin wave reflects and generates additional westward propagating equatorial Rossby waves. The volume transport associated with these waves causes the westward advection of low-salinity north and south of the equator, impacting the tropical ocean circulation.

Climatic links between monthly precipitation in Turkey and the El Niño and La Niña events using the empirical methodology of Ropelewski and Halpert are investigated. Coherent and significant precipitation responses to both the extreme phases of the southern oscillation (SO) are found in two core regions, namely western Anatolia (WA) and eastern Anatolia (EA). The geographical extent of the two regions, together with a defined signal season for each tropical event, are identified. For WA, the April-July wet period during El Niño events is the season when the teleconnection is strong and consistent. For EA, the February-June wet period during El Niño events is found to be the signal season having high rates of coherence and consistency. The occurrence of the signal season (the dry period of April-October) during La Niña events appears to be less significant in EA according to the hypergeometric model. Moreover, the annual cycle analysis implies somewhat of a modulation of regional precipitation in the WA and EA regions during the relevant signal season. From other perspectives, correlation results of seasonal precipitation and seasonal SO index values confirm the implied teleconnections, and the powers of line spectra corresponding to the El Niño occurrences supply some indications. The final aim of this work is to show some guidance for quantification of the SO-related precipitation teleconnections for the core regions by examining shifts in precipitation amounts at various percentiles as a function of the SO extremes. Overall, the results of this investigation are in good agreement with previous relevant studies (especially global-scale type) that try to understand complex global circulation dynamics. In conclusion, mid-latitude precipitation responses to the extreme phases of the SO are detectable in the climate of Turkey.

The Cordillera Blanca of Peru (Central Andes) has the highest elevation in the country, and is mostly affected by tropical and regional climate forcings. Spectral techniques are applied to temperature and precipitation records in order to discern the hidden periodicities and to correlate the influence of different climate forcing indexes that are also submitted to analysis. Similar periodicities are found for Madden-Julian oscillation (MJO) and intra-and interseasonal scale temperature events; the Humboldt Current and South American low-level jet (SALLJ) periodicities are close to annual meteorological events, and El Niño-Southern Oscillation (ENSO) and Intertropical Convergence Zone (ITCZ) displacements are correlated with interannual scale temperature and precipitation events.

Reference evapotranspiration (ETo) is an important hydroclimatic variable for water planning and management. This research explored the potential of using the Climate Forecast System, version 2 (CFSv2), for seasonal predictions of ETo over the states of Alabama, Georgia, and Florida. The 12-km ETo forecasts were produced by downscaling coarse-scale ETo forecasts from the CFSv2 retrospective forecast archive and by downscaling CFSv2 maximum temperature (Tmax), minimum temperature (Tmin), mean temperature (Tmean), solar radiation (Rs), and wind speed (Wind) individually and calculating ETo using those downscaled variables. All the ETo forecasts were calculated using the Penman–Monteith equation. Sensitivity coefficients were evaluated to quantify how and how much does each of the variables influence ETo. Two statistical downscaling methods were tested: 1) spatial disaggregation (SD) and 2) spatial disaggregation with quantile mapping bias correction (SDBC). The downscaled ETo from the...