Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment Research Articles

Assessing the Ocean Surface Current Impact on Scatterometer (C- and Ku-Bands) and Altimeter (Ka-Band) Derived Winds in the Bay of Bengal

A 2-year data set from Indian Space Research Organizations (ISRO's) scatterometer mission (SCATSAT-1) has been used to investigate the impact of ocean surface current on the derived winds in the Bay of Bengal. For this purpose, wind speed residuals obtained between Ku-band SCATSAT-1 and buoy were regressed with buoy measured ocean surface currents. Results show a good agreement between wind residuals and surface current under stable air-sea interaction conditions for the region signifying a considerable impact of currents on the radar backscatter. A further analysis was carried out to ascertain the quantitative impact of currents on the C-band ASCAT derived winds and Ka-band SARAL/AltiKa derived wind speed. This study showed that impact of surface current is much higher on Ka-band altimeter-derived wind speed when compared to C-band and Ku-band scatterometer-derived wind speed. The correlation coefficient so obtained is found to be -0.34 in the case of Ka-band and nearly -0.26 for C-band and Ku-band scatterometer-derived winds. Higher correlation magnitude in the case of Ka-band suggests that surface current impact is slightly more for Ka-band when compared to C- and Ku-bands. These statistics suggest that wind speed retrieved from radar systems are indeed current relative and not fixed earth relative. Basin scale analysis for the Bay of Bengal indicates that surface current feedback in the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE) flux formulation results in 5%-15% reduction in the mechanical energy input to the ocean.

An Observational Study of Entrainment Rate in Deep Convection

This study estimates entrainment rate and investigates its relationships with cloud properties in 156 deep convective clouds based on in-situ aircraft observations during the TOGA-COARE (Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment) field campaign over the western Pacific. To the authors’ knowledge, this is the first study on the probability density function of entrainment rate, the relationships between entrainment rate and cloud microphysics, and the effects of dry air sources on the calculated entrainment rate in deep convection from an observational perspective. Results show that the probability density function of entrainment rate can be well fitted by lognormal, gamma or Weibull distribution, with coefficients of determination being 0.82, 0.85 and 0.80, respectively. Entrainment tends to reduce temperature, water vapor content and moist static energy in cloud due to evaporative cooling and dilution. Inspection of the relationships between entrainment rate and microphysical properties reveals a negative correlation between volume-mean radius and entrainment rate, suggesting the potential dominance of homogeneous mechanism in the clouds examined. In addition, entrainment rate and environmental water vapor content show similar tendencies of variation with the distance of the assumed environmental air to the cloud edges. Their variation tendencies are non-monotonic due to the relatively short distance between adjacent clouds.

Cloud‐resolving simulation of TOGA‐COARE using parameterized large‐scale dynamics

Variations in deep convective activity during the 4 month Tropical Ocean Global Atmosphere‐Coupled Ocean Atmosphere Response Experiment (TOGA‐COARE) field campaign are simulated using a cloud‐resolving model (CRM). Convection in the model is coupled to large‐scale vertical velocities that are parameterized using one of two different methods: the damped gravity wave (Damped‐wave) method and the weak temperature gradient (WTG) method. The reference temperature profiles against which temperature anomalies are computed are taken either from observations or from a model integration with no large‐scale vertical motion (but other forcings taken from observations); the parameterized large‐scale vertical velocities are coupled to those temperature (or virtual temperature) anomalies. Sea surface temperature, radiative fluxes, and relaxation of the horizontal mean horizontal wind field are also imposed. Simulations with large‐scale vertical velocity imposed from the observations are performed for reference. The primary finding is that the CRM with parameterized large‐scale vertical motion can capture the intraseasonal variations in rainfall to some degree. Experiments in which one of several observation‐derived forcings is set to its time‐mean value suggest that those which influence direct forcings on the moist static energy budget—surface wind speed and sea surface temperature (which together influence surface evaporation) and radiative cooling—play the most important roles in controlling convection, particularly when the Damped‐wave method is used. The parameterized large‐scale vertical velocity has a vertical profile that is too bottom‐heavy compared to observations when the Damped‐wave method is used with vertically uniform Rayleigh damping on horizontal wind, but is too top‐heavy when the WTG method is used.

Influence of convective processes on the isotopic composition (δ18O and δD) of precipitation and water vapor in the tropics: 1. Radiative‐convective equilibrium and Tropical Ocean–Global Atmosphere–Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE) simulations

Cumulus convection constitutes a key process in the control of tropical precipitation and the vertical transport of atmospheric water. To better understand the influence of convective processes on the isotopic composition of precipitation and water vapor, water stable isotopes (H218O and HDO) are introduced into a single column model including the Emanuel convective parameterization. This paper analyzes unidimensional simulations of the tropical atmosphere in a state of radiative‐convective equilibrium, and simulations forced by data from the Tropical Ocean–Global Atmosphere–Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE). This study shows that deep convective atmospheres are associated with robust isotopic features such as an isotopic composition of the air below the tropical tropopause layer (around 12–13 km) close to the typical values observed in the lower tropical stratosphere, and an isotopic enrichment of the upper tropospheric water that starts well below the tropopause. It highlights the critical role of condensate lofting and convective detrainment in these features, and the role of convective unsaturated downdrafts in the control of the isotopic composition of precipitation. Finally, it shows that the so‐called “amount effect” primarily reveals the influence of large‐scale atmospheric circulation changes on the isotopic composition of the precipitation, and that temperature changes not associated with circulation changes lead to an “anti–amount effect”. The detailed analysis of the physical processes underlying the “amount effect” is presented in a companion paper.

Influence of convective processes on the isotopic composition (δ18O and δD) of precipitation and water vapor in the tropics: 2. Physical interpretation of the amount effect

In the tropics, the proportion of heavier water isotopes in precipitation is anticorrelated with the precipitation amount. The physical processes underlying this so‐called amount effect are still poorly understood and quantified. In the present study, stable water isotopes (H218O and HDO) have been introduced in a single column model including the Emanuel convection parameterization. We investigate the physical processes underlying the amount effect and propose a methodology to quantify their relative contributions. We focus on convective processes, since the idealized framework of the single column models does not allow us to consider the effects of large‐scale horizontal advections of air masses of different isotopic signatures. We show that two kinds of processes predominantly explain the amount effect: first, the reevaporation of the falling rain and the diffusive exchanges with the surrounding vapor; and second, the recycling of the subcloud layer vapor feeding the convective system by convective fluxes. This highlights the importance of a detailed representation of rain evaporation processes to simulate accurately the isotopic composition of precipitation in the tropics. The variability of the isotopic composition on different timescales (from days to months) is also studied using a unidimensional simulation of the Tropical Ocean–Global Atmosphere–Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE) campaign. The amount effect is best observable at intraseasonal or longer timescales. The period of time over which convective activity significantly affects the isotopic composition of precipitation is related to the residence time of water within atmospheric reservoirs.

A phase analysis of vorticity vectors associated with tropical convection

Three new vorticity vectors have been proposed by Gao et al to study the two-dimensional tropical convection. In the present paper, phase relations between surface rain rate and the vorticity vectors are analysed with the calculations of lag correlation coefficients based on hourly zonally-averaged mass-integrated cloud-resolving simulation data. The cloud-resolving model is integrated with the vertical velocity, zonal wind, horizontal thermal and moisture advections, and sea surface temperature observed and derived from tropical ocean global atmosphere – coupled ocean atmosphere response experiment (TOGA-COARE) for 10 days. Maximum local increase of the vertical component of the convective vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interaction between vorticity and zonal gradient of ice heating. While maximum local increase of the vertical component of the moist vorticity vector leads maximum surface rain rate by 2 hours mainly because of the interaction between zonal specific humidity gradient and zonal buoyancy gradient. And the maximum local decrease of the zonal component of the dynamic vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interactions between vorticity and vertical pressure gradient as well as vorticity and buoyancy.

Experimental Dynamical Forecast of an MJO Event Observed during TOGA-COARE Period

With a hybrid atmosphere-ocean coupled model we carried out an experimental forecast of a well documented Madden-Julian Oscillation (MJO) event that was observed during the period of Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE). The observed event, orig- inated in the western Indian Ocean around 6 January 1993, moved eastward with a phase speed of about 6.2 m s −1 and reached the dateline around February 1. The hybrid coupled model reasonably forecasts the MJO initiation in the western Indian Ocean, but the predicted MJO event propagates too slow (~ 4.4 m s −1 ). Results from previous observational studies using unprecedented humidity profiles obtained by NASA Aqua/AIRS satellite sugg- ested that two potential physical processes may be responsible for this model caveat. After improving the cumulus parameterization scheme based on the observa- tions, the model is able to forecast the same event one month ahead. Further sensitivity experiment confirms that the speed-up of model MJO propagation is primarily due to the improved convective scheme. Further, air-sea coupling plays an important role in maintaining the intensity of the predicted MJO. The results here suggest that MJO prediction skill is sensitive to model cumulus

The role of the ocean in the Madden–Julian Oscillation: Implications for MJO prediction

AbstractThe role of coupled processes in the Madden–Julian Oscillation (MJO) is investigated in the European Centre for Medium‐Range Weather Forecasts Monthly Forecasting System.A series of forecasts initialized daily for 47 days during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA‐COARE) period are performed with sea surface temperatures (SSTs) provided by persistence of initial conditions, and coupling to either a full dynamical ocean model with vertical resolution in the upper ocean typical of coupled models (10 m), or, a 1D mixed layer ocean model with high (∼1 m) vertical resolution in the upper ocean.The experiment with the full dynamical model shows improved skill compared with the persisted SST experiment, indicating a role for coupled processes in the MJO. The experiment with the mixed layer model shows a further improvement in skill over the full dynamical ocean, particularly for the phases of the MJO where the convection is active over the Indian Ocean or West Pacific. This further improvement comes about from an enhanced sensitivity of the SST to the surface flux anomalies associated with the MJO.Additional sensitivity experiments reveal that the improved representation of the diurnal cycle which results from the increased vertical resolution is a significant factor in the improved skill of the experiments with the mixed layer model. Copyright © 2007 Royal Meteorological Society

A diagnostic model of the diurnal cycle of sea surface temperature for use in coupled ocean‐atmosphere models

On the basis of a method of estimating the diurnal amplitude of sea surface temperature (SST) as a function of the diurnal integrals of surface heat and momentum fluxes, a parameterization scheme of the diurnal cycle of SST is implemented in a one‐dimensional ocean mixed‐layer model. Many coupled ocean‐atmosphere models using bulk mixed‐layer schemes underestimate the diurnal cycle in sea surface temperature by up to 2°C. This discrepancy is caused by coarse vertical resolution in the upper grid boxes of the ocean components. A simple solution is suggested by adding one extra transient level: a variable‐depth diurnal sublayer within the top model level which accommodates the diurnal buoyancy cycle. A one‐dimensional mixed‐layer model with 10‐m resolution and with sublayer simulates diurnal SSTs close to those observed from the Tropical Ocean Global Atmosphere/Coupled Ocean Atmosphere Response Experiment (TOGA/COARE) with typical errors of about 0.1°C. The impact of improved SSTs on surface heat fluxes is also shown by coupling the one‐dimensional mixed‐layer model with sublayer to an atmospheric boundary layer model.

Diurnal variation of tropical convection during TOGA COARE IOP

Diurnal variation of tropical convection and kinematic and thermodynamic conditions was investigated for different large-scale environments of the convectively active and inactive periods by using satellite observations and surface measurements during the Intensive Observation Period (IOP) of the Tropical Ocean Global Atmosphere/Coupled Ocean-Atmosphere Response Experiment (TOGA/COARE). During the convectively active period, the features of nocturnal convection appear in vertical profiles of convergence, vertical velocity, heat source, and moisture sink. The specific humidity increases remarkably in the middle troposphere at dawn. On the other hand, the altitude of maximum convergence and that of the upward motion is lower during the convectively inactive period. The specific humidity peaks in the lower troposphere in the daytime and decreases in the middle troposphere. Spectral analyses of the time series of the infrared (IR) brightness temperature (TBB) and amounts of rainfall suggest multiscale temporal variation with a prominent diurnal cycle over land and oceanic regions such as the Intensive Flux Array (IFA) and the South Pacific Convergence Zone (SPCZ). Over land, the daily maximum of deep convection associated with cloud top temperature less than 208 K appears at midnight due to the daytime radiative heating and the sea-land breeze. Over the ocean, convection usually tends to occur at dawn for the convectively active period while in the afternoon during the inactive period. Comparing the diurnal variation of convection with large-scale variables, the authors inferred that moisture in the middle troposphere contributes mostly to the development of nocturnal convection over the ocean during the convectively active period.

Space‐time scaling in high‐intensity Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE) storms

A scale‐invariance analysis of rainfall retrieved during the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE) campaign is discussed. As already found in the previous Global Atmospheric Research Program (GARP) Atlantic Tropical Experiment (GATE) rainfall data set, these new analyses of high‐intensity storms confirm the evidence of scale invariance under self‐similar space‐time transformations. A simple interpretation of this space‐time self‐similarity accounting for the hierarchical organization of precipitation patterns is proposed. Finally, a downscaling model based on a log‐Poisson generator is calibrated on the results of the multifractal analysis and applied to the generation of synthetic fields, reproducing observed statistical properties over a wide range of space scales and timescales.

The Interface or Air–Sea Flux Component of the TOGA Coupled Ocean–Atmosphere Response Experiment and Its Impact on Subsequent Air–Sea Interaction Studies*

Abstract The interface or air–sea flux component of the Coupled Ocean–Atmosphere Response Experiment (COARE) of the Tropical Ocean Global Atmosphere (TOGA) research program and its subsequent impact on studies of air–sea interaction are described. The field work specific to the interface component was planned to improve understanding of air–sea interaction in the Tropics by improving the methodology of flux measurements and by collecting a comprehensive set of observations with coverage of a broad range of time and space scales. The strategies adopted for COARE, particularly the on-site intercomparisons, postexperiment studies of instrument performance, and bulk flux algorithm development, ensured the compilation of very high quality data for the basic near-surface meteorological variables and air–sea fluxes. The success in meeting the goals of improved air–sea heat and freshwater fluxes was verified by closure of the ocean heat and freshwater budgets to within 10 W m−2 and 20%, respectively. These result...

Numerical Experiments Examining the Mechanism of Diurnal Variation of Tropical Convection

A regional atmospheric model was used to clarify the mechanisms that drive the diurnal cycle of tropical convection over the western Pacific Ocean. The diurnal cycle of convection was simulated using data from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE). Mechanisms suggested by previous investigators were confirmed through comparison experiments. The diurnal variation in precipitation was simulated without the effect of horizontal differences in radiative cooling between cloudy and clear regions. Horizontal differences of radiative cooling are not the main factor driving diurnal variation. Direct radiative cooling, and cloud radiative cooling effects destabilize the atmosphere during the night. Numerical experiments that reduced cloud radiative cooling demonstrated the importance of the cloud radiative cooling effect rather than the direct radiative cooling effect. Moreover, in the standard experiment, strong cloud radiative cooling appeared at both upper levels and at the top of the boundary layer. The experiment demonstrated that both the upper level cloud radiative cooling, and the boundary layer cloud radiative cooling, are important in driving the diurnal variation of convection. Boundary-layer cloud radiative cooling destabilizes the low layer atmosphere and promotes the development of shallow convection to deep convection. Diurnal variation of water vapor also plays a role in driving diurnal variation of convection. Moisture is transported upward from the boundary layer at night when radiative cooling of the boundary-layer cloud is intensified.

A Lagrangian investigation of vertical turbulent heat fluxes in the upper ocean during Tropical Ocean–Global Atmosphere/Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE)

We investigated the diurnal cycle of the near‐surface ocean temperatures in the western Pacific Warm Pool, using temperature data from drifters with 20 m thermistor chains, during the Coupled Ocean‐Atmosphere Response Experiment (COARE) Intensive Observation Period (December 1992 to February 1993). We estimated turbulent heat fluxes at 20 m as a residual in the hourly heat budget along each drifter trajectory using hourly surface fluxes. Fortnightly averaged turbulent heat fluxes at 20 m were upward during periods of sustained winds, indicating a warming of the daily thermocline by the deeper layers. During calm periods the inferred turbulent heat fluxes were downward. We also calculated the day‐to‐night differences of the turbulent heat fluxes at 20 m as a residual in the budget of the daily cycle of heat content in the upper 20 m. This method largely avoids the uncertainties of surface turbulent heat fluxes. The residual averaged over the 2 month period was negative for the drifters that experienced strong westerly wind conditions (with heat fluxes positive downward). These surprising results for the warm pool region are at odds with what was found earlier from moored measurements in the central Pacific. Interestingly, however, periods characterized by a westerly wind burst during December 1992 to March 1993 contrasted with the periods with weaker winds: during westerly wind bursts the difference was negative, whereas it was positive during calm or warming periods. This is consistent with our analysis of the daily budget and also with other studies in the COARE domain. It confirms that the nighttime mixed layer was usually much deeper than 20 m during this period. However, our estimates are different for drifters deployed north of 1°N than for drifters near or south of the equator, indicating marked spatial variability in the heat budget of the warm pool.

Air-sea turbulence statistics from synthetic aperture radar: An update

A similarity theory based method for calculating turbulence statistics from synthetic aperture radar (SAR) derived 10 m neutral wind speed image sub-scenes was tested. We concentrated on the ability of the method to yield proper estimates of the ratio of reference height to Obukhov length (z/L) and kinematic buoyancy flux (B). The tropical ocean global atmosphere ‐ coupled ocean atmosphere response experiment (TOGA‐COARE) bulk flux algorithm, fed with buoy and mooring data corresponding in space and time to a particular sub-scene, provided a comparison data set. Thirteen case studies were examined covering a wide range of negative air‐sea temperature difference and wind speed. The statistics from the SAR method that we report herein are averages from a 3 × 3 sub-scene grid centered on a particular in situ station for each case study. The correlation coefficient for z/L is 0.77 and that for B is 0.95. The value of z/L produced by the SAR method, averaged over all 13 case studies, is ‐0.15. The standard deviation of z/L from the SAR method, averaged over all 13 case studies, is 0.12. The corresponding values for B are 0.046 m·s‐1K (average) and 0.034 m·s‐1K (standard deviation). The mean difference and root mean square difference (COARE results ‐ SAR results) for the z/L comparisons are ‐0.008 and 0.119, respectively, and the same statistics for the B comparisons are 0.030 m·s‐1K and 0.039 m·s‐1K. Potential sources of error and avenues for future research are briefly discussed.

Scale-recursive assimilation of precipitation data

This paper presents a new statistical method for assimilating precipitation data from different sensors operating over a range of scales. The technique is based on a scale-recursive estimation algorithm which is computationally efficient and able to account for the nested spatial structure of precipitation fields. The version of the algorithm described here relies on a static multiplicative cascade model which relates rainrates at different scales. Bayesian estimation techniques are used to condition rainrate estimates on measurements. The conditioning process is carried out recursively in two sweeps: first from fine to coarse scales and then from coarse to fine scales. The complete estimation algorithm is similar to a fixed interval smoother although it processes data over scale rather than time. We use this algorithm to assimilate radar and satellite microwave data collected during the tropical ocean–global atmosphere coupled ocean–atmosphere response experiment (TOGA-COARE). The resulting rainrate estimates reproduce withheld radar measurements to within the level of accuracy predicted by the assimilation algorithm.

Heat Balance in the Pacific Warm Pool Atmosphere during TOGA COARE and CEPEX

The atmosphere above the western equatorial Pacific warm pool (WP) is an important source for the dynamic and thermodynamic forcing of the atmospheric general circulation. This study uses a high-resolution reanalysis and several observational datasets including Global Precipitation Climatology Project precipitation, Tropical Ocean Global Atmosphere (TOGA) Tropical Atmosphere Ocean moored buoys, and Earth Radiation Budget Experiment, TOGA Coupled Ocean‐Atmosphere Response Experiment (COARE), and Central Equatorial Pacific Experiment (CEPEX) radiation data to examine the details of the dynamical processes that lead to this net positive forcing. The period chosen is the period of two field experiments: TOGA COARE and CEPEX during December 1992‐March 1993. The four months used in the study were sufficient to establish that the warm pool atmosphere (WPA) was close to a state of radiative‐convective‐dynamic equilibrium. The analysis suggests that the large-scale circulation imports about 200 W m22 of sensible heat and about 140 W m22 of latent energy into the WPA mainly through the low-level mass convergence and exports about 420 W m22 potential energy mainly through the upper-level mass divergence. Thus the net effect of the large-scale dynamics is to export about 80 W m22 energy out of the WPA and cool the WPA by about 0.8 K day21. The dynamic cooling in addition to the radiative cooling of about 0.4 K day21 or 40 W m22 leads to a net radiative‐dynamic cooling of about 1.2 K day21 or 120 W m22, which should be balanced by convective heating of the same magnitude. The WPA radiative cooling is only about 0.4 K day21, which is considerably smaller than previously cited values in the Tropics. This difference is largely due to the cloud radiative forcing (CRF), about 70 W m 22, associated with the deep convective cirrus clouds in the WPA, which compensates the larger clear sky radiative cooling. Thus moist convection heats the WPA, not only through the direct convective heating, that is, the vertical eddy sensible heat and latent energy transport, but also through the indirect convective heating, that is, the CRF of deep convective clouds. The CRF of the deep convective clouds has a dipole structure, in other words, strong heating of the atmosphere through convergence of longwave radiation and a comparable cooling of the surface through the reduction of shortwave radiation at the surface. As a result, the deep convective clouds enhance the required atmospheric heat transport and reduce the required oceanic heat transport significantly in the WP. A more detailed understanding of these convective processes is required to improve our understanding of the heat transport by the large-scale circulation in the Tropics.

Sistema convectivo de mesoescala observado no dia 12 de dezembro de 1992 durante TOGA-COARE: Estrutura cinemática e transporte de quantidade de movimento

No dia 12/12/92, durante o experimento de campo TOGA-COARE (Tropical Ocean Global Atmosphere-Coupled Ocean-Atmosphere Response Experiment) uma missão foi efetuada, detectando uma região de convecção a NE da zona chamada de "Intensive Flux Array " (IFA: 1ºN-4ºS, 151-158ºE). Essa região caracterizava-se por apresentar uma circulação ciclônica nos baixos níveis e um fluxo divergente de NE em altitude, caracterizando a atividade convectiva do sistema. A análise das imagens no canal infravermelho do satélite GMS-4 indicava uma discreta propagação do sistema em direção a sudoeste. Os dois aviões WP-3D da "National Oceanic and Atmospheric Administration" (NOAA), utilizando a técnica de varredura FAST (Fore/Aft Scanning Technique), descreveram trajetórias paralelas coordenadas, primeiramente ao longo da linha convectiva e em seguida dentro da região estratiforme do sistema. Os dados de radares Doppler coletados durante essa missão mostravam a existência de células convectivas moderadas, localizadas dentro de uma área de precipitação estratiforme, e células convectivas mais intensas localizadas a sudoeste do sistema. A combinação das porções paralelas das trajetórias de cada avião foi utilizada para restituir o campo de vento 3D, usando a técnica variacional EODD (Extended Overdetermined Dual-Doppler). O campo de vento 3D, derivado dos dados de radar, serviu para estudar as características do sistema observado e para examinar a estrutura dos transportes de quantidade de movimento operado pelo sistema. A estrutura cinemática do sistema mostrou características clássicas, com um fluxo ascendente na frente do sistema que transporta o ar das camadas inferiores para o alto e um fluxo descendente atrás da linha convectiva. Os resultados para os transportes de quantidade de movimento também mostraram características similares a outros casos estudados anteriormente, tais como: (i) o transporte vertical de quantidade de movimento horizontal perpendicular à linha convectiva é amplificador do gradiente, resultando no aumento do seu cisalhamento vertical; (ii) para a componente paralela (v), a divergência vertical do fluxo v reduziu o seu cisalhamento vertical, gerando um transporte redutor do gradiente.

An Ensemble of Convective Systems on 11 February 1993 during TOGA COARE:Morphology, Rainfall Characteristics, and Anvil Cloud Interactions

Abstract An active day during the Coupled Ocean–Atmosphere Response Experiment (COARE) Intensive Observation Period (IOP) is examined in which nine convective systems evolved and moved eastward across the region of shipboard radar coverage in the Intensive Flux Array (IFA) within westerly wind burst conditions. The detailed genesis, morphology, and interactions between these cloud systems are documented from a radar and satellite perspective. One of these systems was a large and complex elliptical cluster, among the largest observed during the Tropical Ocean Global Atmosphere COARE. Multiple, parallel deep convective lines spaced 20–30 km apart and embedded within this system were initially oriented from north-northwest to south-southeast, oblique to the storm motion. Furthermore, the lines underwent counterclockwise realignment as the system moved eastward. The influence of strong lower-tropospheric directional and speed shear on these convective system properties is examined in the context of a dynamic,...

A coupled simulation model for mesoscale airflow and water current

Abstract A model for calculating air–water interaction at the surface of the ocean and a model that numerically simulates the coupled airflow and water current of mesoscale circulation is proposed. The model for calculating air–water interaction has been developed based on theoretical consideration of the boundary layer under the surface of the water. The validity of this model has been verified by a one-dimensional numerical simulation of the ocean mixed layer and a comparison of the results with those of the Japanese Tropical Ocean Global Atmosphere–Coupled Ocean Atmosphere Response Experiment (TOGO-COARE). Good agreement has been obtained between the results calculated by the model and the results of actual measurements, especially for the heat flux into the ocean. These findings indicate that the calculation model developed here represents air–sea interaction accurately. In addition, a simulation model that calculates the two-dimensional airflow and the ocean current simultaneously has been developed, and a numerical experiment regarding sea and land breezes is provided. The results reveal that the coastal upwelling against the sea breeze is induced by the Ekman transport of momentum and heat in the atmosphere and the ocean.