HEAT FLUX AND SURFACE STRESS ON AND NEAR AN ISLAND IN THE TRADE WIND REGION

1962 ◽  
Author(s):  
E. B. Kraus
Keyword(s):  
Heat Flux ◽  
Surface Stress ◽  
Trade Wind ◽  
Wind Region

Measuring the variability of the shallow convective mass flux profiles in the tropical trade wind region

2020 ◽  
Author(s):  
Marcus Klingebiel ◽  
Heike Konow ◽  
Bjorn Stevens
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Mass Flux ◽  
Doppler Radar ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Trade Wind ◽  
Geophysical Research ◽  
Wind Region ◽  
Convective Mass Flux

<p>Mass flux is a key parameter to represent shallow convection in global circulation models. To estimate the shallow convective mass flux as accurately as possible, observations of this parameter are necessary. Prior studies from Ghate et al. (2011) and Lamer et al. (2015) used Doppler radar measurements over a few months to identify a typical shallow convective mass flux profile based on cloud fraction and vertical velocity. In this study, we extend their observations by using long term remote sensing measurements at the Barbados Cloud Observatory (13° 09’ N, 59° 25’ W) over a time period of 30 months and check a hypothesis by Grant (2001), who proposed that the cloud base mass flux is just proportional to the sub-cloud convective velocity scale. Therefore, we analyze Doppler radar and Doppler lidar measurements to identify the variation of the vertical velocity in the cloud and sub-cloud layer, respectively. Furthermore, we show that the in-cloud mass flux is mainly influenced by the cloud fraction and provide a linear equation, which can be used to roughly calculate the mass flux in the trade wind region based on the cloud fraction.</p><p> </p><p>References:<br>Ghate,  V.  P.,  M.  A.  Miller,  and  L.  DiPretore,  2011:   Vertical  velocity structure of marine boundary layer trade wind cumulus clouds. Journal  of  Geophysical  Research: Atmospheres, 116  (D16), doi:10.1029/2010JD015344.</p><p>Grant,  A.  L.  M.,  2001:   Cloud-base  fluxes  in  the  cumulus-capped boundary layer. Quarterly Journal of the Royal Meteorological Society, 127 (572), 407–421, doi:10.1002/qj.49712757209.</p><p>Lamer, K., P. Kollias, and L. Nuijens, 2015:  Observations of the variability  of  shallow  trade  wind  cumulus  cloudiness  and  mass  flux. Journal of Geophysical Research: Atmospheres, 120  (12), 6161–6178, doi:10.1002/2014JD022950.</p>

Precipitation Characteristics of Trade Wind Clouds during RICO Derived from Radar, Satellite, and Aircraft Measurements

2009 ◽  
Vol 48 (3) ◽  
pp. 464-483 ◽  
Author(s):  
Eric R. Snodgrass ◽  
Larry Di Girolamo ◽  
Robert M. Rauber
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Rainfall Rate ◽  
Cloud Base ◽  
Trade Wind ◽  
Cold Pool ◽  
Aircraft Measurements ◽  
Early Afternoon ◽  
Precipitation Characteristics

Abstract Precipitation characteristics of trade wind clouds over the Atlantic Ocean near Barbuda are derived from radar and aircraft data and are compared with satellite-observed cloud fields collected during the Rain in Cumulus over the Ocean (RICO) field campaign. S-band reflectivity measurements Z were converted to rainfall rates R using a Z–R relationship derived from aircraft measurements. Daily rainfall rates varied from 0 to 22 mm day−1. The area-averaged rainfall rate for the 62-day period was 2.37 mm day−1. If corrected for evaporation below cloud base, this value is reduced to 2.23 mm day−1, which translates to a latent heat flux to the atmosphere of 63 W m−2. When compared with the wintertime ocean-surface latent heat flux from this region, the average return of water to the ocean through precipitation processes within the trade wind layer during RICO was 31%–39%. A weak diurnal cycle was observed in the area-averaged rainfall rate. The magnitude of the rainfall and the frequency of its occurrence had a maximum in the predawn hours and a minimum in the midmorning to early afternoon on 64% of the days. Radar data were collocated with data from the Multiangle Imaging Spectroradiometer (MISR) to develop relationships between cloud-top height, cloud fraction, 866-nm bidirectional reflectance factor (BRF), and radar-derived precipitation. The collocation took place at the overpass time of ∼1045 local time. These relationships revealed that between 5.5% and 10.5% of the cloudy area had rainfall rates that were > 0.1 mm h−1, and between 1.5% and 3.5% of the cloudy area had rainfall rates that were >1 mm h−1. Cloud-top heights between ∼3 and 4 km and BRFs between 0.4 and 1.0 contributed ∼50% of the total rainfall. For cloudy pixels having detectable rain, average rainfall rates increased from ∼1 to 4 mm h−1 as cloud-top heights increased from ∼1 to 4 km. Rainfall rates were closely tied to the type of mesoscale organization, with much of the rainfall originating from shallow (<5 km) cumulus clusters shaped as arcs associated with cold-pool outflows.

Evolution of Organized Shallow Convection

2020 ◽  
Author(s):  
Hauke Schulz ◽  
Ryan Eastman ◽  
Bjorn Stevens
Keyword(s):  
Large Fraction ◽  
Satellite Image ◽  
Atmospheric Environment ◽  
Trade Wind ◽  
Shallow Convection ◽  
Cumulus Clouds ◽  
Back Trajectories ◽  
Wind Region ◽  
Future Warming ◽  
Cloud Patterns

<p>Uncertainty in the response of clouds to warming is the leading source of uncertainty in projections of future warming. To a large fraction the frequently occurring shallow cumulus clouds in the trade wind region contribute to this uncertainty. In symbiosis with thin clouds of stratiform extent they often create various cloud patterns.<br><br>We introduce a neural network that is able to detect the mesoscale organization from GOES16 and MODIS satellite imagery in order to put eight years of ground-based measurements of the Barbados Cloud Observatory into the context of mesoscale organization. With this combination of long-term ground-based measurements from the trade-wind region and satellite image classifications, we overcome the common resolution limitations of satellite derived cloud products of shallow cumuli and are able to present the characteristics of shallow convection depending on the mesoscale organization with great detail.<br><br>By using back-trajectories and EUREC4A field campaign data, we show that differences in the atmospheric environment are not only present at the time of pronounced mesoscale organization, but are already distinguishable days ahead in LTS, wind speed and SST.</p>

scholarly journals Feedback of Tropical Instability-Wave-Induced Atmospheric Variability onto the Ocean

2007 ◽  
Vol 20 (23) ◽  
pp. 5842-5855 ◽  
Author(s):  
Hyodae Seo ◽  
Markus Jochum ◽  
Raghu Murtugudde ◽  
Arthur J. Miller ◽  
John O. Roads
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Surface Stress ◽  
Climate Model ◽  
Ocean Currents ◽  
Ocean Current ◽  
Instability Wave ◽  
Ekman Pumping ◽  
Equatorial Atlantic

Abstract The effects of atmospheric feedbacks on tropical instability waves (TIWs) in the equatorial Atlantic Ocean are examined using a regional high-resolution coupled climate model. The analysis from a 6-yr hindcast from 1999 to 2004 reveals a negative correlation between TIW-induced wind perturbations and TIW-induced ocean currents, which implies damping of the TIWs. On the other hand, the feedback effect from the modification of Ekman pumping velocity by TIWs is small compared to the contribution to TIW growth by baroclinic instability. Overall, the atmosphere reduces the growth of TIWs by adjusting its wind response to the evolving TIWs. The analysis also shows that including ocean current (mean + TIWs) in the wind stress parameterization reduces the surface stress estimate by 15%–20% over the region of the South Equatorial Current. Moreover, TIW-induced perturbation ocean currents can significantly alter surface stress estimations from scatterometers, especially at TIW frequencies. Finally, the rectification effect from the atmospheric response to TIWs on latent heat flux is small compared to the mean latent heat flux.

scholarly journals Tropical Atlantic Moisture Flux, Convection over Northeastern Brazil, and Pertinence of the PIRATA Network*

2005 ◽  
Vol 18 (12) ◽  
pp. 2093-2101 ◽  
Author(s):  
Bruno Durand ◽  
Jacques Servain ◽  
Henri Laurent ◽  
Luiz A. T. Machado
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Negative Correlation ◽  
Moisture Flux ◽  
Northeastern Brazil ◽  
Trade Wind ◽  
Tropical Atlantic ◽  
Correlation Pattern ◽  
Positive Correlation

Abstract This study aims to examine the relationship between the tropical Atlantic latent heat flux and convective cloud coverage over northeast Brazil (NEB) during the four months of the main rainy season (February–May). The correlation with anomalies of these data is investigated, both without lag and with a 1-month lag (the heat flux in advance). In both cases, a significant positive correlation appears in the northwestern tropical Atlantic, and a significant negative correlation is obtained for a limited area off eastern NEB. These two correlation patterns are linked to anomalies in the trade wind intensity and in the meridional position of the intertropical convergence zone (ITCZ), which relate to the latent heat flux anomalies and NEB convective coverage anomalies, respectively. The positive correlation pattern is spread over a large part of the northern tropical Atlantic, whereas the negative correlation pattern is confined off NEB. This indicates the existence of different regional mechanisms in the tropical Atlantic basin. The impact of the Atlantic heat fluxes on NEB convection is somewhat different from the classical meridional dipole related to the SST variability. The analysis of the horizontal moisture flux shows that during flood years an additional meridional inflow balances the eastward loss, and the upward velocity reinforced over NEB contributes to intensify NEB convection. The positive correlation pattern indicates that the location of the northern branch of the Pilot Research moored Array in the Tropical Atlantic (PIRATA) moorings is pertinent to monitor the ocean–atmosphere interface parameters. The negative correlation pattern off NEB provides new support for the possible extension of the PIRATA array toward the Brazilian coast. Complementary results at 1-month lag and the real-time availability of the PIRATA data confirm the potential of NEB forecasting.

Effects of Sea Spray on Tropical Cyclones Simulated under Idealized Conditions

2008 ◽  
Vol 136 (5) ◽  
pp. 1686-1705 ◽  
Author(s):  
Jeffrey S. Gall ◽  
William M. Frank ◽  
Young Kwon
Keyword(s):  
Heat Flux ◽  
Surface Layer ◽  
Latent Heat ◽  
Surface Wind ◽  
Heat Fluxes ◽  
Sea Spray ◽  
High Wind ◽  
Near Surface ◽  
Wind Region ◽  
Spray Droplets

Abstract Under high-wind conditions, breaking waves and whitecaps eject large numbers of sea spray droplets into the atmosphere. The spray droplets originate with the same temperature and salinity as the ocean surface and thus increase the effective surface area of the ocean in contact with the atmosphere. As a result, the spray alters the total sensible and latent heat fluxes in the near-surface layer. The spray drops in the near-surface layer also result in horizontal and vertical spray-drag effects. The mass of the spray introduces an additional drag in the vertical momentum equation and tends to stabilize the lower boundary layer (BL). An initially axisymmetric control hurricane was created from the output of a real-data simulation of Hurricane Floyd (1999) using the nonhydrostatic fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5, version 3.4). The subsequent simulations, however, are not axisymmetric because the mass, wind, and spray fields are allowed to develop asymmetries. While such a design does not result in an axisymmetric simulation, the mass, wind, and spray fields develop more realistic structures than in an axisymmetric simulation. Simulations of the hurricane were conducted using a version of the Fairall et al. (1994) sea spray parameterization, which includes horizontal and vertical spray-drag effects. The simulations were run using varying spray-source function intensities and with and without horizontal and vertical spray-drag effects. At present, the relationship of spray production to surface wind speed is poorly known for hurricane-force wind regimes. Results indicate that spray modifies the hurricane structure in important but complex ways. Spray moistens the near-surface layer through increased evaporation. The effect of spray on the near-surface temperature profile depends on the amount of spray and its location in the hurricane. For moderate spray amounts, the near-surface layer warms within the high-wind region of the hurricane and cools at larger radii. For larger spray amounts, the near-surface layer warms relative to the moderate spray case. The moderate spray simulations (both with and without drag effects) have little net effect on the hurricane intensity. However, in the heavier spray runs, the total sensible heat flux is enhanced by 200 W m−2, while the total latent heat flux is enhanced by over 150 W m−2 in the high-wind region of the storm. Horizontal spray drag decreases wind speeds between 1 and 2 m s−1, and vertical spray drag increases the stability of the lower BL. In these heavy spray runs, the effect of the enhanced spray sensible and latent heat fluxes dominates the negative spray-drag effects, and as a result, the modeled storm intensity is upward of 10 mb stronger than the control run by the end of the simulation time. This study shows that spray has the capability of significantly affecting hurricane structure, but to do so, the amount of spray ejected into the BL of the hurricane would need to lie near the upper end of the currently hypothesized spray-source functions.

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