Deep Convection

Deep water formation is not only the driver of the global ocean circulation; by sending heat and carbon to the deep ocean, it is also crucial for climate change mitigation. Yet its future is uncertain: will it slow down as stratification increases, emerge in polar regions as the wind starts blowing over previously ice-covered waters, or intensify with increased evaporation? Here we present the first global study of the evolution of deep water formation as atmospheric CO2 concentration increases, using the latest generation of Earth System models (CMIP6). We show that open ocean deep convection stops globally shortly before 600 ppm, mostly in response to increased stratification, but that deep water formation continues under a different regime. Deep convection does not emerge in ice-freed regions. The mechanism is self-reinforcing, as less mixing also increases stratification and modifies heat fluxes, with most oceanic regions gaining even more heat. By establishing a direct connection between the sea surface and the ocean, deep water formation is crucial for ventilation and a driver of the global ocean circulation 1,2,3 . Moreover, by bringing excess anthropogenic heat and carbon to the deep ocean where they can be stored instead of staying in the atmosphere, deep water formation in fact currently mitigates climate change 4,5 . There are many regions where "chimneys" of deep water formation have been observed. The first such region to be monitored was in the Western Mediterranean, where strong winds blowing from the south of France in winter cause very deep mixed layers 6 . It has since been found to also occur in the Eastern Mediterranean, in the Adriatic and Aegean seas 7 . The most "famous" regions are in the North Atlantic, namely in the Labrador -Irminger seas and in the Nordic Seas 8,9,10,11,12 . There, deep waters regularly form as a result of the strong winds blowing from Greenland 8,9 and sea ice processes 8,9,13 . These same two processes cause deep mixing in the enclosed East Sea / Sea of Japan 14 . The last known location in the northern hemisphere is by Rockall Trough (north of Scotland), again in response to strong winds 15 . At the other end of the world in the Southern Ocean, current observations suggest that deep waters are formed mostly from shelf processes 16 , so that deep convection happens more seldom, in association with open ocean polynyas 8,9,17,18 .

The Galvez-Davison Index (GDI) is a stability index developed to improve the prediction of thunderstorms and shallower types of moist convection in the tropics. The motivation was the need of a skillful index to forecast tropical convection, particularly in the Caribbean, where traditional stability indices struggle as they were designed with extra tropical latitudes in mind. The GDI focuses on thermodynamic properties of the low and mid troposphere. It is calculated from temperatures and mixing ratios available at 500, 700, 850 and 950 hPa. It can therefore be easily computed from radiosonde data, other analyses or model data. The GDI considers three physical processes that modulate tropical convection: (1) the simultaneous availability of heat and moisture in the mid and low troposphere, (2) the stabilizing/destabilizing effects of a warmer/cooler mid troposphere in association with ridges/troughs and (3) the entrainment of dry air and stabilization associated with subsidence inve...

In the autumn of 1996 the field component of an experiment designed to observe water mass transformation began in the Labrador Sea. Intense observations of ocean convection were taken in the following two winters. The purpose of the experiment was, by a combination of meteorological and oceanographic field observations, laboratory studies, theory, and modeling, to improve understanding of the convective process in the ocean and its representation in models. The dataset that has been gathered far exceeds previous efforts to observe the convective process anywhere in the ocean, both in its scope and range of techniques deployed. Combined with a comprehensive set of meteorological and air-sea flux measurements, it is giving unprecedented insights into the dynamics and thermodynamics of a closely coupled, semienclosed system known to have direct influence on the processes that control global climate.

Between 1996 and 1998, a concerted effort was made to study the deep open ocean convection in the Labrador Sea. Both in situ observations and numerical models were employed with close collaboration between the researchers in the fields of physical oceanography, boundary layer meteorology, and climate. A multitude of different methods were used to observe the state of ocean and atmosphere and determine the exchange between them over the experiment's period. The Labrador Sea Deep Convection Experiment data collection aims to assemble the observational data sets in order to facilitate the exchange and collaboration between the various projects and new projects for an overall synthesis. A common file format and a browsable inventory have been used so as to simplify the access to the data.

Turbulence and coherent circulation structures, such as submesoscale and mesoscale eddies, convective plumes and Langmuir cells, play a critical role in shaping phytoplankton spatial distribution and population dynamics. We use a framework of advection-reaction-diffusion equations to investigate the effects of turbulent transport on the phytoplankton population growth and its spatial structure in a vertical two-dimensional vortex flow field. In particular, we focus on how turbulent flow velocities and sinking influence phytoplankton growth and biomass aggregation. Our results indicate that conditions in mixing and growth of phytoplankton can drive different vertical spatial structures in the mixed layer, with the depth of the mixed layer being a critical factor to allow coexistence of populations with different sinking speed. With increasing mixed layer depth, positive growth for sinking phytoplankton can be maintained with increasing turbulent flow velocities, allowing the apparent...

This study aims to identify the vertical transport mechanisms that uplifted the forest fire emissions from Sumatra to the upper troposphere during the June 2013 haze crisis. WRF-Chem is used to simulate the formation and transport of biomass-burning haze during the study period of 18 th to 26 th June 2013. The South-Southeast Asian synoptic weather patterns and their effects on the transport of biomass-burning emissions from Sumatra to Peninsular Malaysia were studied computationally to explain the phenomenon. Results show that PM 10 emissions were lifted to 200 hPa height (approximately 12 km) over the Strait of Malacca on 24 th June. The two identified vertical transport mechanisms confirmed a previously conjectured convergence over the Strait of Malacca and orographic lifting over Peninsular Malaysia. These mechanisms were able to uplift the biomass-burning emissions to the upper troposphere and this could have significant long-range transport and global climatic effects.

A new diagnostic convective closure, which is dependent on convective available potential energy (CAPE), is derived under the quasi-equilibrium assumption for the free troposphere subject to boundary layer forcing. The closure involves a convective adjustment time scale for the free troposphere and a coupling coefficient between the free troposphere and the boundary layer based on different time scales over land and ocean. Earlier studies with the ECMWF Integrated Forecasting System (IFS) have already demonstrated the model’s ability to realistically represent tropical convectively coupled waves and synoptic variability with use of the “standard” CAPE closure, given realistic entrainment rates.A comparison of low-resolution seasonal integrations and high-resolution short-range forecasts against complementary satellite and radar data shows that with the extended CAPE closure it is also possible, independent of model resolution and time step, to realistically represent nonequilibrium ...

There has been a progressive deepening of winter convection in the Labrador Sea since 2012, with the individual profile maximum depth exceeding 1800 m since 2014 and reaching 2100 m in 2016. This increase, during repeated positive phases of the winter North Atlantic Oscillation (NAO), resembles that during the formation of the record depth (2500 m) Labrador Sea Water (LSW) class in 1987–1994, attributed to repeated positive NAO forcing having provided critical preconditioning. The 2012–2016 LSW class is one of the deepest and most persistent ever observed (back to 1938). Year‐round observations from profiling Argo floats since 2002 complemented by annual surveys are providing novel information on the seasonal‐to‐decadal evolution of LSW, such as its variable density, the recent multiyear preconditioning, and its 2016 density being the highest since the mid‐1990s. These findings should help international observation programs and numerical model studies investigating LSW influences on...

This paper presents findings on the correlation between surface air temperature and lightning activity in Colombia. The air temperature data spans several decades, while the lightning data covers 17 years. The temperature records come from nine cities, and the lightning data covers about 50% of the territory. Despite differences in sampling rates and dataset sizes, the findings show a positive correlation between surface air temperature and lightning activity, suggesting a possible relationship between warmer conditions and increased lightning activity.

An approach to determine the convective available potential energy (CAPE) and the convective inhibition (CIN) based on the use of data from a Raman lidar system is illustrated in this work. The use of Raman lidar data allows to provide high temporal resolution measurements (5 min) of CAPE and CIN and follow their evolution over extended time periods covering the full cycle of convective activity. Lidar-based measurements of CAPE and CIN are obtained from Raman lidar measurements of the temperature and water vapour mixing ratio profiles and the surface measurements of temperature, pressure and dew point temperature provided by a surface weather station. The approach is applied to the data collected by the Raman lidar system BASIL in the frame of COPS. Attention was focused on 15 July and 25-26 July 2007. Lidar-based measurements are in good agreement with simultaneous measurements from radiosondes and with estimates from different mesoscale models.

Here, we revisit the existing concepts of the vertical structure of deep layers in the Black Sea using data from sensors deployed on profiling floats. The deep transition layer (DTL) between 700 and 1,700 m acts as an interface between the baroclinic layer and the largest bottom convective layer (BCL) of the world oceans. On top of DTL are the warm intermediate layer and deep cold intermediate layer. They both showed strong trends in the last 15 years due to warmer climate and intensification of warmer intrusions from Bosporus. A “salinity wave” was detected in 2005–2009 below ∼1,700 m, which evidenced for the first time the penetration of gravity flow from Bosporus down to the bottom. The layering of water masses was explained as resulting from the different distribution of sources of heat and salt, double diffusion, and balances between the geothermal and salinity flows in the BCL.

Analyses of recent helioseismic data indicate that the dynamical regimes at the base of the convection zone can be different from those observed at the top, having either significantly shorter periods or non-periodic behaviour. Recently spatiotemporal fragmentation/bifurcation has been proposed as a dynamical mechanism to account for the multi-mode behaviour that is possibly observed in the solar convection zone, without requiring separate physical mechanisms with different time scales at different depths. Here we study the robustness of this mechanism with respect to changes to the zero order rotation profile, motivated by the uncertainties of and differences between the various reductions of the helioseimic data. We find that spatiotemporal fragmentation is a common feature of the reductions investigated.

As trocas horizontais e verticais de energia para um composto de sete episódios de Zona de Convergência do Atlântico Sul (ZCAS), foram estudadas a partir da decomposição em modos normais, considerando-se a partição vertical de energia entre os modos externo e internos, e as interferências entre os modos horizontais de oscilação Rossby, Kelvin, Misto Rossby-Gravidade, Gravidade Oeste e Leste. Um máximo de porcentagem de energia total (aproximadamente 60%) é observado para os modos internos 4 a 7, com alturas equivalentes entre 100 e 600 metros, especialmente sobre grande parte da América do Sul central e próximo ao equador, incluindo a região da ZCAS. À medida que a latitude aumenta, a energia é distribuída para os modos mais externos (n=1 a 3). Para a partição horizontal de energia, as maiores contribuições foram obtidas para as auto-interações dos modos Rossby e Kelvin e interações cruzadas Rossby-Kelvin, em todas as categorias de modos verticais, sendo estas últimas responsáveis pelas interferências construtivas de energia na região da ZCAS. As interações entre modos verticais mostraram um aumento da porcentagem de energia dos Baixos Níveis para a Estratosfera, com máxima interferência positiva (negativa) de energia em Altos Níveis (Estratosfera), para os modos internos 4 a 7. Palavras Chave: Energética, Modos Normais, Zona de Convergência do Atlântico Sul (ZCAS).

The last two years have seen many countries in South East Asia, Central and South America severely affected by transboundary smoke haze originating from uncontrolled forest fires, burning mainly in tropical forests severely affected by drought. The magnitude of these events was largely unpredicted and unprecedented, and understandably governments were anxious for advice about health impacts on their populations along with steps that could be taken to mitigate the problems. In the absence of global guidelines for dealing with such emergencies, the WHO is currently faced with the difficult task of developing workable guidelines for dealing with forest fire emissions and their impact on human health and well-being.

The planetary boundary layer includes the portion of the atmosphere which is directly influenced by the presence of the Earth's surface. Aerosol particles trapped within the PBL can be used as tracers to study boundary-layer vertical structure and time variability. The PBL height and structure can be estimated based on the use of Raman lidar data. The method is based on the first order derivative of the range-corrected elastic signal (RCS), which is a modified version of the method defined by Seibert et al. [1] and Sicard et al. [2]. Estimates of the PBL height and structure are obtained from the above mentioned approach are compared with simultaneous estimates obtained from potential temperature profiles determined from the radiosondes launched simultaneously to lidar operation. Additional estimates of the boundary layer height are obtained from rotational Raman lidar signals, used for temperature measurements signals. Preliminary results and correlation are illustrated and discussed.

This paper examines the cyclogenesis of the ''Perfect Storms'' of late October and early November 1991 over the North Atlantic and focuses on the influence of Hurricane Grace (HG) toward their development. The two storms considered are the ''Perfect Storm'' (PS) that underwent a warm seclusion process and an extratropical cyclone (EC1) with two development phases. HG, which initially formed via tropical transition (TT), influenced the first phase of EC1 via reduced atmospheric static stability and enhanced low-level baroclinicity. As a result, deep moist convection and latent heat release produced maxima in midtropospheric diabatic heating and lower-tropospheric potential vorticity (PV) that aided the development of EC1. Backward air parcel trajectories and large diabatic contributions to eddy available potential energy (APE) generation suggests that EC1 developed as a diabatic Rossby vortex (DRV)-like feature. The second and explosively deepening phase of EC1 occurred as the cyclone coupled with an uppertropospheric PV disturbance (PVD) over the eastern North Atlantic. Backward air parcel trajectories demonstrate the explosive deepening of EC1 involved airstreams originating from east of HG and from over the Labrador Sea. Parcel trajectories and a large baroclinic contribution to eddy APE generation further suggests that the two-phase development of EC1 may have involved a DRV-like feature. The subsequent recurvature and extratropical transition (ET) of HG occurred in the warm sector of the PS downstream of a second upper-tropospheric PVD over the western North Atlantic. Reduced atmospheric static stability, enhanced warm air advection, and strong latent heat release during the recurvature and ET of HG contributed to the development of a strong, zonally oriented warm front and the warm seclusion of the PS. Parcel trajectory analysis demonstrates that the PS warm seclusion involved the isolation of air parcels by a bent-back warm front that were warmed via sensible heating from the underlying Gulf Stream.

Influences of time-dependent precipitation on water mass transformation and heat budgets in an idealized marginal sea are examined using theoretical and numerical models. The equations proposed by Spall in 2012 are extended to cases with time-dependent precipitation whose form is either a step function or a sinusoidal function. The theory predicts the differences in temperature and salinity between the convective water and the boundary current as well as the magnitudes of heat fluxes into the marginal sea and across the sea surface. Moreover, the theory reveals that there are three inherent time scales: relaxation time scales for temperature and salinity and a precipitation time scale. The relaxation time scales are determined by a steady solution of the theoretical model with steady precipitation. The relaxation time scale for temperature is always smaller than that for salinity as a result of not only the difference in the form of fluxes at the surface but also the variation in the eddy transport from the boundary current. These three time scales and the precipitation amplitude determine the strength of the ocean response to changes in precipitation and the phase relation between precipitation, changes in salinity and temperature, and changes in heat fluxes. It is demonstrated that the theoretical predictions agree qualitatively well with results from the eddy-resolving numerical model. This demonstrates the fundamental role of mesoscale eddies in the ocean response to time-dependent forcing and provides a framework with which to assess the extent to which observed variability in marginal sea convection and water mass transformation are consistent with an external forcing by variations in precipitation.

During the 'Convective and Orographically-induced Precipitation Study' (COPS) performed in summer 2007, deep convection developed on July 15, although convective available potential energy was only moderate and convective inhibition was high. Convection was restricted to an area east of the Black Forest crest. Data analysis revealed that the convection was triggered by different mechanisms. Due to a surface high which was situated east of the Black Forest and a surface low which approached the investigation area from the west, a mesoscale convergence zone was established between the two regions and moved eastwards. Secondly, high insolation favoured the development of slope and valley winds and high evapotranspiration resulted in an increase of moisture in the planetary boundary layer (PBL). The thermally driven circulation systems formed a convergence zone along the mountain crest. When the synoptically induced mesoscale convergence zone reached the Black Forest, the different convergence zones superimposed optimally, such that strong updraughts were observed above the mountain. These updraughts penetrated the PBL-capping inversion and nearly reached the level of free convection. About 15 min after the convergence zone had passed the Black Forest crest, first clouds developed east of it. While moving further eastwards, the convergence zone intensified and became visible as a north-south oriented cloud line in the satellite images. Some deep convective cells with precipitation formed within the cloud line. The dense COPS network allowed the capture of the position and characteristics of the convergence zone and explains why convection developed in some restricted areas only.

Long‐lasting mesoscale convective systems (MCSs) may occur in the outer region of tropical cyclones in the western North Pacific, especially in conjunction with the southwest monsoon as in the case of Typhoon Morakot that caused great flooding and landslides in Taiwan. These “outer‐MCSs” are linear convective systems that develop from distant rainbands, have a large cold cloud shield, and last more than six hours. These outer‐MCSs are important for typhoon rainfall forecasting because of the torrential rainfall when they interact with land and terrain to produce serious flooding that is separate from the rainfall near the center. A total of 109 outer‐MCSs that occurred during 1999–2009 are identified using infrared and passive microwave images. About 22% of all typhoons in the western North Pacific have at least one outer‐MCS during their life cycle. In 85% of the QuikSCAT oceanic 10‐m wind observations of outer‐MCSs, positive shear vorticity on the left side of mesoscale surface je...

Since 1999, the increased frequency of dry conditions over East Africa, particularly during the March-May (MAM) season, has heightened concerns in a region already highly insecure about food. The underlying mechanisms, however, are still not yet fully understood. This article analyses a proxy for daily convection variations over a large region encompassing East Africa and the whole Indian Ocean basin by applying a cluster analysis to more than 30 years of daily outgoing longwave radiation (OLR). Focusing on the MAM season to investigate relationships with East African long rains, four recurrent convection regimes associated with wet/dry conditions in East Africa are identified. Interestingly, all four regimes are related to western/central Pacific sea surface temperatures (SSTs) and rainfall. Wet regimes are associated with cool and dry/warm and wet conditions over the Maritime Continent (MC)/tropical Pacific east of the date line. Dry regimes exhibit opposite SST/rainfall dipole patterns in the Pacific compared to wet regimes, with the Indian Ocean found to modulate impacts on East African rainfall. Significant relationships between off-equatorial warming in the west Pacific and a more frequent dry regime in May since 1998-1999 suggest an earlier onset of the monsoon and Somali jet, consistent with the recent abrupt shift observed in East African long rains and their modulation at multi-decadal time scales of the Pacific.

The South Adriatic (SA) is an entry point for water masses originating from the Ionian Sea (IS) and a place of dense water formation for the eastern Mediterranean deep circulation cell. Water masses, entering the SA in larger amount during the winter, show decadal variability explained by different circulating regimes (cyclonic and anticyclonic) in the IS, referred to as "Bimodal Oscillating System" (BiOS). Sampling station was situated in the South Adriatic Pit (SAP) with depth of 1200m. Micro-and nano-phytoplankton abundances, biomass, community structure, physical and chemical properties are presented in the winter and spring months for five consecutive years (2009)(2010)(2011)(2012)(2013) during different circulating regimes of BiOS. Winter convective mixing was regularly observed in February except in winter of 2011 which had effect on nutrient availability and consequently on biomass of primary producers. Strong convecting mixing results in higher diatom abundances comparing to winter without mixing. Different circulation regimes also had an effect on community structure resulting in absence of coccolithophorids in years of cyclonic circulation regime.

By exploiting an abundant number of extreme storms observed simultaneously by the Global Precipitation Measurement (GPM) mission Core Observatory satellite’s suite of sensors and by the ground-based S-band Next Generation Weather Radar (NEXRAD) network over the continental United States, proxies for the identification of hail are developed from the GPM Core Observatory satellite observables. The full capabilities of the GPM Core Observatory are tested by analyzing more than 20 observables and adopting the hydrometeor classification on the basis of ground-based polarimetric measurements being truth. The proxies have been tested using the critical success index (CSI) as a verification measure. The hail-detection algorithm that is based on the mean Ku-band reflectivity in the mixed-phase layer performs the best of all considered proxies (CSI of 45%). Outside the dual-frequency precipitation radar swath, the polarization-corrected temperature at 18.7 GHz shows the greatest potential for...

We examined long-range statistical forecasting methods for Korean summer precipitation (KSP). We reviewed existing literature on the East Asian summer monsoon to develop a background on current KSP research and on the relationship of KSP to climate variations. Second, we explored interannual variability of KSP using composite and correlation analyses. We found that circulation anomalies in the spring prior to the monsoon in the tropical northwest Pacific alter sea surface temperatures (SST). These SST anomalies then persist into the following summer, leading to summer circulation anomalies that alter the flow into Korea and the precipitation on the seasonal scale. From this relationship, we developed a seasonal forecasting index. Third, we looked at KSP on the intraseasonal scale, to develop statistical forecast methods with five to thirty day leadtimes. We found that the Korean summer monsoon onset, break and withdrawal are positively correlated to the El Niño / La Niña state. We found that the Madden-Julian Oscillation (MJO), when conditioned with our seasonal index, showed skill in forecasting with lead times out to 20 days. Last, we found that tropical cyclone activity in Korea is impacted by ENSO on the interannual scale, and MJO on the intraseasonal scale. 15. NUMBER OF PAGES 145

Using a two-year dataset (2016–17) from 17 one-minute rain gauges located in the moist forest region of Ghana, the performance of Integrated Multisatellite Retrievals for GPM, version 6b (IMERG), is evaluated based on a subdaily time scale, down to the level of the underlying passive microwave (PMW) and infrared (IR) sources. Additionally, the spaceborne cloud product Cloud Property Dataset Using SEVIRI, edition 2 (CLAAS-2), available every 15 min, is used to link IMERG rainfall to cloud-top properties. Several important issues are identified: 1) IMERG’s proneness to low-intensity false alarms, accounting for more than a fifth of total rainfall; 2) IMERG’s overestimation of the rainfall amount from frequently occurring weak convective events, while that of relatively rare but strong mesoscale convective systems is underestimated, resulting in an error compensation; and 3) a decrease of skill during the little dry season in July and August, known to feature enhanced low-level cloudin...

Labrador Sea winter convection forms a cold, fresh and dense water mass, Labrador Sea Water, that sinks to the intermediate and deep layers and spreads across the ocean. Convective mixing undergoes multi-year cycles of intensification (deepening) and relaxation (shoaling), which have been also shown to modulate long-term changes in the atmospheric gas uptake by the sea. Here I analyze Argo float and ship-based observations to document the 2012-2023 convective cycle. I find that the highest winter cooling for the 1994-2023 period was in 2015, while the deepest convection for the 1996-2023 period was in 2018. Convective mixing continued to deepen after 2015 because the 2012-2015 winter mixing events preconditioned the water column to be susceptible to deep convection in three more years. The progressively intensified 2012-2018 winter convections generated the largest and densest class of Labrador Sea Water since 1995. Convection weakened afterwards, rapidly shoaling by 800 m per year in the winters of 2021 and 2023. Distinct processes were responsible for these two convective shutdowns. In 2021, a collapse and an eastward shift of the stratospheric polar vortex, and a weakening and a southwestward shift of the Icelandic Low resulted in extremely low surface cooling and convection depth. In 2023, by contrast, convective shutdown was caused by extensive upper layer freshening originated from extreme Arctic sea-ice melt due to Arctic Amplification of Global Warming. The Labrador Sea is the coldest (Fig. 1) and freshest deep subpolar North Atlantic (SPNA) basin 1 where intense vertical mixing driven by high winter surface heat losses (WSHL) produces Labrador Sea Water (LSW)-a major North Atlantic intermediate-depth water mass 2-8. Cold fresh dense oxygenrich LSW spreads across the ocean renewing and ventilating its intermediate and deeper layers 9-15. The LSW formation process, deep convection, defines interannual and longer-term trends in these layers 15-20 , spins the North Atlantic Subpolar Gyre 21 and affects the exchanges between the Subpolar and Subtropical Gyres 22,23. LSW enters 19,24 and, arguably, controls 25,26 the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). The contribution of the Labrador Sea to the AMOC was recently challenged by the Overturning of the Subpolar North Atlantic Program (OSNAP), reporting it to be much lower 27 than, e.g., the volumetricallydefined LSW export 7. It should be noted that there are arguable reasons for an underestimation of the Labrador Sea contribution based on the OSNAP observations. Only a few of these reasons are given below. The interior LSW recirculation and exit flows, present on the seaward sides of the moorings, are not accounted for by the OSNAP array. LSW spreading from the Labrador Sea (Fig. 1d, e) to the Irminger Sea and Iceland Basin 10-12 is entrained by the boundary currents and dense overflows in vicinities of the continental slope and rise, and Mid-Atlantic Ridge 19 , thus contributing to the AMOC outside the LSW source (the entrainment of LSW by the Iceland-Scotland Overflow Water will be revisited in the "Results" section). Located outside the deep convection zone in the central Labrador Sea, the OSNAP array is exposed to convection in the eastern part, reducing the Labrador Sea contribution there. Lacking vertical resolution and accuracy, the mooring-based density measurements underestimate the LSW thickness changes entering the transport calculations. Identifying and understanding the limitations, omissions, and inconsistencies in the OSNAP observations will allow us to address and resolve the controversies in results and improve the program design.

Significance Turbulent convection in horizontally extended systems comprises vortices and plumes on many time and length scales. These structures interact nonlinearly to self-organize into slowly evolving turbulent superstructures, which are horizontally more extended than in height. We use a U-shaped deep-learning algorithm to generate a time-varying planar network, resulting in a drastic reduction of degrees of freedom, and use it to detect the 3D superstructures and estimate their effectiveness in transporting heat. We thus demonstrate the likely utility of deep learning for parameterizing convection in global models of atmospheric and stellar convection whenever mesoscale structures are conspicuous.

The role of environmental moisture in the deepening of cumulus convection is investigated by means of cloud-resolving numerical experiments. Under idealized conditions of uniform SST and specified radiative cooling, the evolution of trade wind cumulus into congestus clouds, and ultimately deep convection, is simulated and analyzed. The results exhibit a tight coupling between environmental moisture and cloud depth, both of which increase over the course of the simulations. Moistening in the lower troposphere is shown to result from the detrainment of water vapor from congestus clouds, and the strength of this tendency is quantified. Moistening of the lower troposphere reduces the dilution of cloud buoyancy by dry-air entrainment, and the relationship between this effect and increasing cloud depth is examined. The authors confirm that the mixing of water vapor by subgrid-scale turbulence has a significant impact on cloud depth, while the mixing of sensible heat has a negligible effect. By contrast, the dependence of cloud depth on CAPE appears to be of secondary importance. However, the deepening trend observed in these simulations is not solely determined by the evolving mean vapor profile. While enhancing the horizontally averaged humidity does result in deeper clouds, this occurs only after an adjustment period of several hours, presumably because of the buildup of CAPE. The implications of these findings for large-scale simulations in which resolved mixing is reduced-for example, by coarser spatial resolution or 2D experiments-are also discussed.

This study aims to identify the vertical transport mechanisms that uplifted the forest fire emissions from Sumatra to the upper troposphere during the June 2013 haze crisis. WRF-Chem is used to simulate the formation and transport of biomass-burning haze during the study period of 18 th to 26 th June 2013. The South-Southeast Asian synoptic weather patterns and their effects on the transport of biomass-burning emissions from Sumatra to Peninsular Malaysia were studied computationally to explain the phenomenon. Results show that PM 10 emissions were lifted to 200 hPa height (approximately 12 km) over the Strait of Malacca on 24 th June. The two identified vertical transport mechanisms confirmed a previously conjectured convergence over the Strait of Malacca and orographic lifting over Peninsular Malaysia. These mechanisms were able to uplift the biomass-burning emissions to the upper troposphere and this could have significant long-range transport and global climatic effects.

The influences of precipitation on water mass transformation and the strength of the meridional overturning circulation in marginal seas are studied using theoretical and idealized numerical models. Nondimensional equations are developed for the temperature and salinity anomalies of deep convective water masses, making explicit their dependence on both geometric parameters such as basin area, sill depth, and latitude, as well as on the strength of atmospheric forcing. In addition to the properties of the convective water, the theory also predicts the magnitude of precipitation required to shut down deep convection and switch the circulation into the haline mode. High-resolution numerical model calculations compare well with the theory for the properties of the convective water mass, the strength of the meridional overturning circulation, and also the shutdown of deep convection. However, the numerical model also shows that, for precipitation levels that exceed this critical threshold, the circulation retains downwelling and northward heat transport, even in the absence of deep convection.

The Nordic seas are commonly described as a single basin to investigate their dynamics and sensitivity to environmental changes when using a theoretical framework. Here, we introduce a conceptual model for a two-basin marginal sea that better represents the Nordic seas geometry. In our conceptual model, the marginal sea is characterized by both a cyclonic boundary current and a front current as a result of different hydrographic properties east and west of the midocean ridge. The theory is compared to idealized model simulations and shows good agreement over a wide range of parameter settings, indicating that the physics in the two-basin marginal sea is well captured by the conceptual model. The balances between the atmospheric buoyancy forcing and the lateral eddy heat fluxes from the boundary current and the front current differ between the Lofoten and the Greenland Basins, since the Lofoten Basin is more strongly eddy dominated. Results show that this asymmetric sensitivity leads to opposing responses depending on the strength of the atmospheric buoyancy forcing. Additionally, the front current plays an essential role for the heat and volume budget of the two basins, by providing an additional pathway for heat toward the interior of both basins via lateral eddy heat fluxes. The variability of the temperature difference between east and west influences the strength of the different flow branches through the marginal sea and provides a dynamical explanation for the observed correlation between the front current and the slope current of the Norwegian Atlantic Current in the Nordic seas.

Scientific basis for the emergence of deep convection in the tropics at or above 28øC sea-surface temperature (SST), and its proximity to the highest observed SST of about 30øC, is explained from first principles of moist convection and TOGA-COARE data. Our calculations show that SST of 28-29øC is needed for charging the cloud-base airmass with the required moist static energy for clouds to reach the upper troposphere (i.e., 200 hPa). Besides reducing solar irradiation by cloud-cover, moist convection also produces cool and dry downdrafts, which promote oceanic cooling by increased sensible and latent heat fluxes at the surface. Consequently, the tropical ocean seesaws between the states of net energy absorber before, and net energy supplier after, the deep moist convection, which causes the SST to vacillate between 280 and 30øC. While dynamics of the largescale circulation embodying the easterly waves and Madden-Julian Oscillations (MJOs) modulate moist convection, we show that the quasi-stationary vertical profile of moist static energy of the tropics is the ultimate cause of the upper limit on tropical SSTs. the Tropical Ocean Global Atmosphere-Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE) data, Boocollected in the Intensive Observations Periods (IOP), from a single IMET buoy due to Woods Hole Oceanographic Institute-01 Nov 1992 through 28 Feb 1993 (Weller and Anderson, 1996), and radar derived rainfall (Short et al., 1997) in support of our explanation. Also General Science Corporation, Contractor on-site, NASA/GSFC.

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as

Intense tropical convection that overshoots deep into the Tropical Tropopause Layer (TTL) is thought to play an important role in influencing the region’s moisture content. However, the net effect of such convection and the details of how it affects TTL humidity are still not well understood. Furthermore, the degree of this influence is dependent on the statistics of overshooting convection, such as its frequency, areal extent and depth, which may differ between different convective regimes. This thesis first examines the key physical processes that govern the net influence of overshooting convection on TTL water vapour when it penetrates into different observed TTL environments, one supersaturated and the other subsaturated (with respect to ice), using idealised three-dimensional cloud-resolving simulations. It then investigates the characteristics of overshooting convection during a convectively active monsoon regime and a ‘break’ period, using ground-based radar data from the Tro...

The NASA ER-2 and DC-8 aircraft collected remote sensing and in situ data sets from Hurricane Bonnie (23, 24, and 26 August 1998) during the Convection And Moisture Experiment-3 (CAMEX-3). Bonnie was an exceptional case where NASA and NOAA had five aircraft sampling both upper levels and lower altitudes. The ER-2 was instrumented with the ER-2 Doppler X-Band radar (EDOP) and several radiometers ranging from visible to lower frequency microwaves. EDOP is a fixed dual-beam radar (nadir and forward-looking beams) which allows computation of both vertical and alongtrack horizontal winds. The hurricane secondary circulation is typically difficult to measure at upper levels due to aircraft altitude limitations and sensitivity of the lower altitude airborne radars. EDOP is in principle, well suited to measure these components of the wind. When ER-2 flies across the approximate center of the hurricane circulation, the along-track winds derived from EDOP, are approximately equal to the hurricane radial flow comprising the secondary circulation. Assuming that

We propose a dynamical interpretation of model projections for an end‐of‐century wetting in equatorial East Africa. In the current generation of global climate models, increased atmospheric moisture content associated with warming is not the dominant process explaining the increase in rainfall, as the regional circulation is only weakly convergent even during the rainy seasons. Instead, projected wetter future conditions are generally consistent with the El Niño‐like trend in tropical Pacific sea surface temperatures in climate models. In addition, a weakening in moisture convergence over the adjacent Congo Basin and Maritime Continent cores of convection results in the weakening of near‐surface winds, which increases moisture advection from the Congo Basin core toward the East African margin. Overall confidence in the projections is limited by the significant biases in simulation of the regional climatology and disagreement between observed and modeled tropical Pacific sea surface ...

Jamie K. Wolff1*, Pedro Jimenez2, Jimy Dudhia3, Gary Lackmann4, Kelly Mahoney5 and Michelle Harrold1 1National Center for Atmospheric Research/Research Applications Laboratory and Developmental Testbed Center 2División de Energías Renovables, CIEMAT, Madrid, Spain 3National Center for Atmospheric Research Earth System Laboratory 4North Carolina State University 5Cooperative Institute for Research in the Atmosphere/NOAA Earth System Research Laboratory P77

Spatial-temporal submesoscale variabilities in the upper Red Sea and their 3 generation mechanisms, including frontogenesis, mixed-layer instability (MLI), 4 and symmetric instability (SI) are qualitatively investigated using high-resolution 5 simulations. The results suggest that submesoscales are critical hydrodynamic 6 components and stirring at submesoscale has a clear signal in the Red Sea,

Spatial-temporal submesoscale variabilities in the upper Red Sea and their 3 generation mechanisms, including frontogenesis, mixed-layer instability (MLI), 4 and symmetric instability (SI) are qualitatively investigated using high-resolution 5 simulations. The results suggest that submesoscales are critical hydrodynamic 6 components and stirring at submesoscale has a clear signal in the Red Sea,

High vertical resolution CloudSat radar measurements, supplemented with cloud boundaries and aerosol information from the CALIPSO lidar, are used to examine radiative heating features in the atmosphere that have not previously been characterized by passive sensors. The monthly and annual-mean radiative heating/cooling structure for a four-year period between 2006 and 2010 is derived. The mean atmospheric radiative cooling rate from CloudSat/CALIPSO is 0.98 K d-1 (1.34 K d-1 between 150 and 950 hPa) and is largely a reflection of the earth's mean water vapor distribution, with sharp vertical gradients introduced by clouds. It is found that there is a minimum in cooling in the tropical lower to middle troposphere, a cooling maximum in the upper boundary layer of the Southern Hemisphere poleward of-10° latitude, and a minimum in cooling in the lower boundary layer in the mid-to high latitudes of both hemispheres. Clouds tops tend to strongly cool the upper boundary layer all year in the mid-to high latitudes of the Southern Hemisphere (where peak seasonal mean winter cooling is 3.4 K d-1), but this cooling is largely absent in the corresponding parts of the Northern Hemisphere during boreal winter, resulting in a hemispheric asymmetry in cloud radiative cooling.

High vertical resolution CloudSat radar measurements, supplemented with cloud boundaries and aerosol information from the CALIPSO lidar, are used to examine radiative heating features in the atmosphere that have not previously been characterized by passive sensors. The monthly and annual-mean radiative heating/cooling structure for a four-year period between 2006 and 2010 is derived. The mean atmospheric radiative cooling rate from CloudSat/CALIPSO is 0.98 K d -1 (1.34 K d -1 between 150 and 950 hPa) and is largely a reflection of the earth's mean water vapor distribution, with sharp vertical gradients introduced by clouds. It is found that there is a minimum in cooling in the tropical lower to middle troposphere, a cooling maximum in the upper boundary layer of the Southern Hemisphere poleward of -10° latitude, and a minimum in cooling in the lower boundary layer in the mid-to high latitudes of both hemispheres. Clouds tops tend to strongly cool the upper boundary layer all year in the mid-to high latitudes of the Southern Hemisphere (where peak seasonal mean winter cooling is 3.4 K d -1 ), but this cooling is largely absent in the corresponding parts of the Northern Hemisphere during boreal winter, resulting in a hemispheric asymmetry in cloud radiative cooling.

A simple two-layer model, the moist-convective rotating shallow water, which allows for low-cost high-resolution numerical simulations of the dynamics of the moist atmosphere in the presence of topography, is used to identify and understand dynamical processes governing the evolution of easterly waves propagating on the background of a low-latitude easterly jet crossing a land-sea boundary, a setup crudely representing the African Easterly Jet over the West-African plateau and the Atlantic ocean. We perform a thorough linear stability analysis and identify the unstable modes of the jet, which we use then for initialisation of fully nonlinear numerical simulations. In this way we determine nonlinear evolution of unstable perturbations of the jet, both in the "dry" and moist-convective environments, and highlight essential differences between the two cases. We identify a mechanism of formation of intense lower-layer cyclonic vortices at the northern flank of the jet, and determine the influence of the land-sea contrast upon this process.

The dependence of entrainment rate on environmental conditions and cloud characteristics is investigated using large eddy simulations (LES) of the response of shallow cumulus convection to a small-amplitude temperature perturbation that is horizontally uniform and localized in height. The simulated cumulus fields are analyzed in the framework of an ensemble of entraining plumes by tracking a large number of Lagrangian parcels embedded in the LES and grouping them into different plumes based on their detrainment heights. The results show that fractional entrainment rate per unit height of a plume is inversely proportional to the plume's vertical velocity and its distance to the cloud edge, while changes in environmental stratification and relative humidity, the plume's buoyancy, or the vertical gradient of its buoyancy due to the temperature perturbation have little effect on the plume's entrainment rate.