scholarly journals Influence of El Niño Wind Stress Anomalies on South Brazil Bight Ocean Volume Transports

2015 ◽  
Vol 2015 ◽  
pp. 1-15 ◽  
Author(s):  
Luiz Paulo de Freitas Assad ◽  
Carina Stefoni Böck ◽  
Rogerio Neder Candella ◽  
Luiz Landau
Keyword(s):  
Stress Field ◽  
Interannual Variability ◽  
Wind Stress ◽  
Large Scale ◽  
Time Lag ◽  
Surface Wind ◽  
Circulation Model ◽  
Volume Transport ◽  
Wind Stress Field ◽  
Volume Transports

The knowledge of wind stress variability could represent an important contribution to understand the variability over upper layer ocean volume transports. The South Brazilian Bight (SBB) circulation had been studied by numerous researchers who predominantly attempted to estimate its meridional volume transport. The main objective and contribution of this study is to identify and quantify possible interannual variability in the ocean volume transport in the SBB induced by the sea surface wind stress field. A low resolution ocean global circulation model was implemented to investigate the volume transport variability. The results obtained indicate the occurrence of interannual variability in meridional ocean volume transports along three different zonal sections. These results also indicate the influence of a wind driven large-scale atmospheric process that alters locally the SBB and near-offshore region wind stress field and consequently causes interannual variability in the upper layer ocean volume transports. A strengthening of the southward flow in 25°S and 30°S was observed. The deep layer ocean volume transport in the three monitored sections indicates a potential dominance of other remote ocean processes. A small time lag between the integrated meridional volume transports changes in each monitored zonal section was observed.

scholarly journals An Empirical Model for Surface Wind Stress Response to SST Forcing Induced by Tropical Instability Waves (TIWs) in the Eastern Equatorial Pacific

2009 ◽  
Vol 137 (6) ◽  
pp. 2021-2046 ◽  
Author(s):  
Rong-Hua Zhang ◽  
Antonio J. Busalacchi
Keyword(s):  
Wind Stress ◽  
Empirical Model ◽  
Stress Responses ◽  
Large Scale ◽  
Climate Models ◽  
Surface Wind ◽  
Microwave Remote Sensing ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
Sst Forcing

Abstract High-resolution space-based observations reveal significant two-way air–sea interactions associated with tropical instability waves (TIWs); their roles in budgets of heat, salt, momentum, and biogeochemical fields in the tropical oceans have been recently demonstrated. However, dynamical model-based simulations of the atmospheric response to TIW-induced sea surface temperature (SSTTIW) perturbations remain a great challenge because of the limitation in spatial resolution and realistic representations of the related processes in the atmospheric planetary boundary layer (PBL) and their interactions with the overlying free troposphere. Using microwave remote sensing data, an empirical model is derived to depict wind stress perturbations induced by TIW-related SST forcing in the eastern tropical Pacific Ocean. Wind data are based on space–time blending of Quick Scatterometer (QuikSCAT) Direction Interval Retrieval with Thresholded Nudging (DIRTH) satellite observations and NCEP analysis fields; SST data are from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). These daily data are first subject to a spatial filter of 12° moving average in the zonal direction to extract TIW-related wind stress (τTIW) and SSTTIW perturbations. A combined singular value decomposition (SVD) analysis is then applied to these zonal high-pass-filtered τTIW and SSTTIW fields. It is demonstrated that the SVD-based analysis technique can effectively extract TIW-induced covariability patterns in the atmosphere and ocean, acting as a filter by passing wind signals that are directly related with the SSTTIW forcing over the TIW active regions. As a result, the empirical model can well represent TIW-induced wind stress responses as revealed directly from satellite measurements (e.g., the structure and phase), but the amplitude can be underestimated significantly. Validation and sensitivity experiments are performed to illustrate the robustness of the empirical τTIW model. Further applications are discussed for taking into account the TIW-induced wind responses and feedback effects that are missing in large-scale climate models and atmospheric reanalysis data, as well as for uncoupled ocean and coupled mesoscale and large-scale air–sea modeling studies.

Simulation of the Diurnal Cycle in Tropical Rainfall and Circulation during Boreal Summer with a High-Resolution GCM

2010 ◽  
Vol 138 (9) ◽  
pp. 3434-3453 ◽  
Author(s):  
Jeffrey J. Ploshay ◽  
Ngar-Cheung Lau
Keyword(s):  
Diurnal Cycle ◽  
General Circulation ◽  
Large Scale ◽  
Surface Wind ◽  
Circulation Model ◽  
Horizontal Resolution ◽  
Boreal Summer ◽  
Tropical Rainfall ◽  
Early Afternoon ◽  
Seaward Migration

Abstract The simulation of the diurnal cycle (DC) of precipitation and surface wind pattern by a general circulation model (GCM) with a uniform horizontal resolution of 50 km over the global domain is evaluated. The model output is compared with observational counterparts based on datasets provided by the Tropical Rainfall Measuring Mission and reanalysis products of the European Centre for Medium-Range Weather Forecasts. The summertime diurnal characteristics over tropical regions in Asia, the Americas, and Africa are portrayed using the amplitude and phase of the first harmonic of the 24-h cycle, departures of data fields during selected hours from the daily mean, and differences between extreme phases of the DC. There is general agreement between the model and observations with respect to the large-scale land–sea contrasts in the DC. Maximum land precipitation, onshore flows, and landward migration of rainfall signals from the coasts occur in the afternoon, whereas peak maritime rainfall and offshore flows prevail in the morning. Seaward migration of precipitation is discernible over the western Bay of Bengal and South China Sea during nocturnal and morning hours. The evolution from low-intensity rainfall in the morning/early afternoon to heavier precipitation several hours later is also evident over selected continental sites. However, the observed incidence of rainfall with very high intensity in midafternoon is not reproduced in the model atmosphere. Although the model provides an adequate simulation of the daytime upslope and nighttime downslope winds in the vicinity of mountain ranges, valleys, and basins, there are notable discrepancies between model and observations in the DC of precipitation near some of these orographic features. The model does not reproduce the observed seaward migration of precipitation from the western coasts of Myanmar (Burma) and India, and from individual islands of the Indonesian Archipelago at nighttime.

The role of oceanic internal instabilities on the Great Whirl interannual variability 

2021 ◽  
Author(s):  
Kwatra Sadhvi ◽  
Iyyappan Suresh ◽  
Takeshi Izumo ◽  
Jérôme Vialard ◽  
Matthieu Lengaigne ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Sea Level ◽  
Wind Stress ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Offshore Wind ◽  
Intrinsic Variability ◽  
Wind Stress Curl ◽  
Sea Level Anomalies

<p>The Great Whirl (GW) is a quasi-permanent anticyclonic eddy that appears every summer monsoon in the western Arabian Sea off the horn of Africa. It generally forms in June, peaks in July-August, and dissipates afterward. While the annual cycle of the GW has been previously described, its year-to-year variability has been less explored. Satellite observations reveal that the leading mode of summer interannual sea-level variability in this region is associated with a typically ~100-km northward or southward shift of the GW. This shift is associated with coherent sea surface temperature and surface chlorophyll signals, with warmer SST and reduced marine primary productivity in regions with positive sea level anomalies and vice versa. Eddy-permitting (~25 km) and eddy-resolving (~10 km) ocean general circulation model simulations reproduce the observed pattern reasonably well, even in the absence of interannual variations in the surface forcing. This implies that the GW interannual variability partly arises from oceanic internal instabilities. Ensemble oceanic simulations further reveal that this stochastic oceanic intrinsic variability and the deterministic response to wind forcing each contribute to ~50% of the total GW interannual variability in July-August. The deterministic part appears to be related to the oceanic response  to Somalia alongshore wind stress and offshore wind-stress curl variations during the monsoon onset projecting onto the GW structure, and getting amplified by oceanic instabilities. After August, the stochastic component dominates the GW variability.</p>

scholarly journals Technical Note: Volume Transport Equations in Combined Sverdrup-Stommel-Munk Dynamics without Level of no Motion

2016 ◽  
Author(s):  
Peter C. Chu
Keyword(s):  
Wind Stress ◽  
Surface Wind ◽  
Volume Transport ◽  
Transport Equations ◽  
Ocean Dynamics ◽  
Meridional Transport ◽  
Surface Wind Stress ◽  
Forcing Function ◽  
Forcing Functions ◽  
Sverdrup Transport

Abstract. The cornerstone theories of ocean dynamics proposed by Sverdrup (1947), Stommel (1948), and Munk (1950) are based on the assumption of level of no motion. Such an assumption is the same as the assumption of no meridional geostrophic transport. Ever since Sverdrup (1947) however, verification of the accuracy of the Sverdrup balance theory is based on the comparison of the Sverdrup meridional transport with the meridional transport calculated directly from the geostrophic currents based on hydrographic data. To overcome the mismatch between theory (no meridional geostrophic transport in Sverdrup transport) and verification (comparison of Sverdrup transport to meridional geostrophic transport), extended Sverdrup-Stommel-Munk transport equations are derived in this note with replacing the level of no motion by the ocean bathymetry and in consequence one forcing function (surface wind stress) in the classical transport equations (with level of no motion assumption) is replaced by five forcing functions: density, surface wind stress, bottom meridional current, bottom stresses due to vertical and horizontal viscosities. The first two forcing functions (density and surface wind stress) are more than an order of magnitude stronger than the other three forcing functions using the world ocean bathymetry, climatological annual mean hydrographic and surface wind stress data. The extended Sverdrup volume transport streamfunctions under wind forcing, density forcing, and combined wind and density forcing are presented.

scholarly journals High-Resolution Satellite Measurements of the Atmospheric Boundary Layer Response to SST Variations along the Agulhas Return Current

2005 ◽  
Vol 18 (14) ◽  
pp. 2706-2723 ◽  
Author(s):  
Larry W. O’Neill ◽  
Dudley B. Chelton ◽  
Steven K. Esbensen ◽  
Frank J. Wentz
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Wind Stress ◽  
Large Scale ◽  
Surface Wind ◽  
Sensible Heat Flux ◽  
Wind Stress Curl ◽  
Return Current ◽  
Short Scale ◽  
Sst Gradient

Abstract The marine atmospheric boundary layer (MABL) response to sea surface temperature (SST) perturbations with wavelengths shorter than 30° longitude by 10° latitude along the Agulhas Return Current (ARC) is described from the first year of SST and cloud liquid water (CLW) measurements from the Advanced Microwave Scanning Radiometer (AMSR) on the Earth Observing System (EOS) Aqua satellite and surface wind stress measurements from the QuikSCAT scatterometer. AMSR measurements of SST at a resolution of 58 km considerably improves upon a previous analysis that used the Reynolds SST analyses, which underestimate the short-scale SST gradient magnitude over the ARC region by more than a factor of 5. The AMSR SST data thus provide the first quantitatively accurate depiction of the SST-induced MABL response along the ARC. Warm (cold) SST perturbations produce positive (negative) wind stress magnitude perturbations, leading to short-scale perturbations in the wind stress curl and divergence fields that are linearly related to the crosswind and downwind components of the SST gradient, respectively. The magnitudes of the curl and divergence responses vary seasonally and spatially with a response nearly twice as strong during the winter than during the summer along a zonal band between 40° and 50°S. These seasonal variations closely correspond to seasonal and spatial variability of large-scale MABL stability and surface sensible heat flux estimated from NCEP reanalysis fields. SST-induced deepening of the MABL over warm water is evident in AMSR measurements of CLW. Typical annual mean differences in cloud thickness between cold and warm SST perturbations are estimated to be about 300 m.

scholarly journals The influence of high‐resolution wind stress field on the power input to near‐inertial motions in the ocean

2013 ◽  
Vol 40 (18) ◽  
pp. 4882-4886 ◽  
Author(s):  
Antonija Rimac ◽  
Jin‐Song Storch ◽  
Carsten Eden ◽  
Helmuth Haak
Keyword(s):  
High Resolution ◽  
Stress Field ◽  
Wind Stress ◽  
Power Input ◽  
Wind Stress Field
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