Influence Of Sea Surface Temperature Research Articles

Pacific SST influence on spring precipitation in Addis Ababa, Ethiopia

ABSTRACTRecent periods of drought in Ethiopia and other parts of East Africa have highlighted the growing importance of producing reliable forecasts of seasonal precipitation. Key in deriving such forecasts is a good understanding of the atmospheric and oceanic drivers of different precipitation regimes. In Ethiopia and other parts of East Africa, interannual variability of precipitation depends on variations in sea surface temperature (SST) and atmospheric circulation on both regional and global scales. Links between summer precipitation in Ethiopia and large‐scale modes of climate variability such as El Niño Southern Oscillation (ENSO) have previously been established but the influence of global SST on spring precipitation has not yet been fully explored. Here, we analyse the links between Pacific SST and precipitation in Addis Ababa, Ethiopia for a century‐long period (1900–2004). A tripole correlation pattern between spring precipitation and SST in the Pacific basin is found. We develop regression‐based models to estimate spring precipitation from Pacific SST with a lead time of two to three months. When subject to cross‐validation, models based on principal component multiple linear regression (PC‐MLR) calibrated on Pacific SST during December show substantial skill in reproducing observed temporal variability in Addis Ababa precipitation during February (r = 0.48) and March (r = 0.40), and the period spanning February to April (r = 0.44). Our findings suggest that the inclusion of Pacific SST in predictive models may benefit drought forecasting across Ethiopia.

Extended optimal estimation techniques for sea surface temperature from the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI)

Sea surface temperature (SST) can be estimated from day and night observations of the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) by optimal estimation (OE). We show that exploiting the 8.7μm channel, in addition to the “traditional” wavelengths of 10.8 and 12.0μm, improves OE SST retrieval statistics in validation. However, the main benefit is an improvement in the sensitivity of the SST estimate to variability in true SST.In a fair, single-pixel comparison, the 3-channel OE gives better results than the SST estimation technique presently operational within the Ocean and Sea Ice Satellite Application Facility. This operational technique is to use SST retrieval coefficients, followed by a bias-correction step informed by radiative transfer simulation. However, the operational technique has an additional “atmospheric correction smoothing”, which improves its noise performance, and hitherto had no analogue within the OE framework. Here, we propose an analogue to atmospheric correction smoothing, based on the expectation that atmospheric total column water vapour has a longer spatial correlation length scale than SST features. The approach extends the observations input to the OE to include the averaged brightness temperatures (BTs) of nearby clear-sky pixels, in addition to the BTs of the pixel for which SST is being retrieved. The retrieved quantities are then the single-pixel SST and the clear-sky total column water vapour averaged over the vicinity of the pixel. This reduces the noise in the retrieved SST significantly. The robust standard deviation of the new OE SST compared to matched drifting buoys becomes 0.39K for all data. The smoothed OE gives SST sensitivity of 98% on average. This means that diurnal temperature variability and ocean frontal gradients are more faithfully estimated, and that the influence of the prior SST used is minimal (2%). This benefit is not available using traditional atmospheric correction smoothing.

Global air temperature variability independent of sea-surface temperature influences

Mean global surface air temperature (SAT) and sea surface temperature (SST) display substantial variability on timescales ranging from annual to multi-decadal. We review the key recent literature on connections between global SAT and SST variability. Although individual ocean influences on SAT have been recognized, the combined contributions of worldwide SST variability on the global SAT signal have not been clearly identified in observed data. We analyze these relations using principal components of detrended SST, and find that removing the underlying combined annual, decadal, and multi-decadal SST variability from the SAT time series reveals a nearly monotonic global warming trend in SAT since about 1900.

Influence of local and remote SST on North Atlantic tropical cyclone potential intensity

We examine the role of local and remote sea surface temperature (SST) on the tropical cyclone potential intensity in the North Atlantic using a suite of model simulations, while separating the impact of anthropogenic (external) forcing and the internal influence of Atlantic Multidecadal Variability. To enable the separation by SST region of influence we use an ensemble of global atmospheric climate model simulations forced with historical, 1856–2006 full global SSTs, and compare the results to two other simulations with historical SSTs confined to the tropical Atlantic and to the tropical Indian Ocean and Pacific. The effects of anthropogenic plus other external forcing and that of internal variability are separated by using a linear, “signal-to-noise” maximizing EOF analysis and by projecting the three model ensemble outputs onto the respective external forcing and internal variability time series. Consistent with previous results indicating a tampering influence of global tropical warming on the Atlantic hurricane potential intensity, our results show that non-local SST tends to reduce potential intensity associated with locally forced warming through changing the upper level atmospheric temperatures. Our results further indicate that the late twentieth Century increase in North Atlantic potential intensity, may not have been dominated by anthropogenic influence but rather by internal variability.

Effects of the PDO Phase on the Tropical Belt Width

Recent studies have shown that the tropical belt (TB) has progressively expanded since at least the late 1970s. This trend has been largely attributed to the radiative forcing due to greenhouse gas (GHG) increase and stratospheric ozone depletion, even if an influence of sea surface temperature (SST) anomalies has been also suggested. The impact of the Pacific decadal oscillation (PDO) on the TB width is investigated in this work. The study is performed by using both Atmospheric Model Intercomparison Project (AMIP) and idealized simulations, produced by the NCAR Community Atmosphere Model, version 3 (CAM3) GCM and reanalysis data [40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), ERA-Interim, and Modern-Era Retrospective Analysis for Research and Applications (MERRA)]. Reanalyses show that a switch of the PDO from a positive to a negative phase can lead to a significant TB expansion during the equinoxes. This effect, indicating a possible PDO contribution to the widening that characterized the TB width during the last decades, is not correctly reproduced by model simulations. Deficiencies in the sensitivity of model-simulated convective processes to SST anomalies are suggested as a possible cause of the TB widening underestimation.

Influence of the Kuroshio in the East China Sea on the Early Summer (Baiu) Rain

Abstract Influence of the Kuroshio in the East China Sea on the baiu rainband is examined using satellite observations, a reanalysis dataset, and a regional atmospheric model from 2003 to 2008. Satellite observations and reanalysis data reveal that precipitation over the Kuroshio is the highest in early summer (June), when the baiu rainband covers the East China Sea. The high rainfall is collocated with the warm sea surface temperature (SST) tongue of the Kuroshio. This locally enhanced precipitation is embedded in the large-scale baiu rainband, so that the amplitude of precipitation over the Kuroshio is twice as large as that in its surrounding area. The Kuroshio is also accompanied by high surface wind speed, energetic evaporation, and wind convergence. This wind convergence likely results from the SST influence on atmospheric pressure through not only temperature changes, but also humidity changes. Furthermore, the Kuroshio anchors the ascent motion and large diabatic heating with a peak in the midtroposphere, suggesting that the influence of the Kuroshio extends to the upper troposphere. It is also found that the East China Sea in June is the region of the strongest deep atmospheric response to western boundary currents along with the Gulf Stream region in summer. The observational results are well reproduced by the regional atmospheric model. The model indicates that when the SST tongue of the Kuroshio is smoothed, the enhanced precipitation, the energetic evaporation, and the wind convergence over the Kuroshio disappear, although the large-scale structure of the baiu rainband is not essentially changed.

Sensitivity of Midlatitude Storm Intensification to Perturbations in the Sea Surface Temperature near the Gulf Stream

The Gulf Stream region is a primary location for midlatitude storm cyclogenesis and growth. However, the influence of sea surface temperature (SST) on storms in the region is still under question, particularly after a storm has developed. Using the Weather Research and Forecasting (WRF) model, a storm that intensified as it transited northward across the Gulf Stream is simulated multiple times using different SST boundary conditions. These experiments test the storm response to changes in both the absolute value of the SST and the meridional SST gradient. Across the different simulations, the storm strength increases monotonically with the magnitude of the SST perturbations, even when the perturbations weaken the SST gradient. The storm response to the SST perturbations is driven by the latent heat release in the storm warm conveyor belt (WCB). During the late stages of development, the surface fluxes under the storm warm sector regulate the supply of heat and moisture to the WCB. This allows the surface fluxes to govern late-stage intensification and control the storm SST sensitivity. The storm warm front also responds to the SST perturbations; however, the response is independent of that of the storm central pressure. These modeling results suggest that the SST beneath the storm can have just as important a role as the SST gradients in local forcing of the storm.

Effects of coastal topography on climate: high-resolution simulation with a regional climate model

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 52:159-174 (2012) - DOI: https://doi.org/10.3354/cr01077 Contribution to the CR Special: 'The regional climate model RegCM4' Effects of coastal topography on climate: high-resolution simulation with a regional climate model Barış Önol* Istanbul Technical University, Aeronautics & Astronautics Faculty, Meteorological Engineering, Maslak, 34469 Istanbul, Turkey *Email: onolba@itu.edu.tr ABSTRACT: High-resolution regional climate simulations driven by NCEP-reanalysis for the eastern Mediterranean (EM) region covering 48 yr (1961−2008) are used to examine the coastal effects over the EM region. The present study uses the ICTP-RegCM3 to downscale to a 10 km resolution over the EM with a 50 km driving nest. The high-resolution simulation captures strong temperature gradients as a result of resolving the steep topography over the eastern Black Sea and Mediterranean coasts of Turkey, as well as the Ionian coast of Greece. In terms of the validation based on the coastal meteorological stations, the annual temperature bias in the high-resolution simulation is <0.7°C for the Black Sea and Mediterranean regions over Turkey and the same bias is 1°C in the 50 km simulation. Moreover, the model is able to capture the observed warming trend in summer temperatures during the last 5 decades. In terms of the precipitation simulation, the error in the 10 km simulation (17%) over the Black Sea region is much lower than that in the 50 km simulation (42%) when considering coastal meteorological stations. In addition, existence of many small islands over the EM domain is another unresolved challenge for climate simulations. The small islands tend to be overwhelmed by the influence of sea-surface temperature, and local climate effects related to topography are suppressed in 10 km temperature simulations. However, the precipitation error in the 10 and 50 km simulations based on the island stations (Crete, Rhodes and Cyprus) over the EM domain are 12 and 24%, respectively. In terms of the cross-section analysis comparing model elevation to simulated precipitation, the implementation of high-resolution simulation illustrates the importance of modeling the complex terrain over the eastern Black Sea and Mediterranean coasts of Turkey, as the precipitation error was reduced to 7 and 18%, respectively. KEY WORDS: Coastal effect on climate · Regional climate modeling · Eastern Mediterranean Full text in pdf format PreviousNextCite this article as: Önol B (2012) Effects of coastal topography on climate: high-resolution simulation with a regional climate model. Clim Res 52:159-174. https://doi.org/10.3354/cr01077 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 52. Online publication date: March 22, 2012 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2012 Inter-Research.

Interannual variability of moisture source over southern Indian Ocean during boreal summer and its relationship with local SST

AbstractIn boreal summer, the southern Indian Ocean (SIO) features more evaporation than precipitation and thus it is a moisture source region for the Asian summer monsoon rainfall. In the present study, the interannual variability of moisture source over the SIO is analysed for boreal summer during 1979‐2008. The impacts of local sea surface temperature (SST) and the El Niño‐Southern Oscillation (ENSO) on the moisture source are compared and the possible mechanisms for the SST influence on the moisture source are investigated. The leading mode of the interannual variation of apparent moisture sink (&lt;Q2&gt;) over the SIO displays an obvious out‐of‐phase relationship over the western‐central SIO and the region to the northwest‐north of Australia. The interannual variations of &lt; Q2&gt; over the above two regions have significant positive correlation with local SST. An increase in local SST enhances convection and ascent, leading to more precipitation. Over the western‐central SIO, surface winds weaken corresponding to higher SST in the western‐central SIO and lower SST to the northwest‐north of Australia, leading to less oceanic evaporation. Thus, the variation of the moisture source over the western‐central SIO is contributed by both precipitation and evaporation. However, the variation of the moisture source to the northwest‐north of Australia is contributed mainly by precipitation. ENSO amplifies anomalous moisture source induced by local SST anomalies. ENSO and local SST work cooperatively to influence the moisture source over the SIO. Copyright © 2012 Royal Meteorological Society

Influence of Sea Surface Temperature on Humidity and Temperature in the Outflow of Tropical Deep Convection

Abstract Multiple years of measurements of tropical upper-tropospheric temperature and humidity by the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) project are analyzed in the vicinity of deep convective outflow to study the variations of temperature and humidity and to investigate the influence of the sea surface temperature (SST) on the outflow air properties. The principal findings are the following. 1) The distribution of relative humidity with respect to ice (RHi) depends on where a convective system is sampled by the MOZAIC aircraft: deep inside the system, RHi is unimodal with the mode at ~114%; near the outskirts of the system, bimodal distribution of RHi starts to emerge with a dry mode at around 40% and a moist mode at 100%. The results are compared with previous studies using in situ measurements and model simulations. It is suggested that the difference in the RHi distribution can be explained by the variation of vertical motions associated with a convective system. 2) Analysis of MOZAIC data shows that a fractional increase of specific humidity with SST, q−1 dq/dSTT, near the convective outflow is about 0.16–0.18 K−1. These values agree well with previous studies using satellite data. Because MOZAIC measurements of temperature and humidity are independent, the authors further analyze the SST dependence of RHi and temperature individually. Temperature increases with SST for both prevalent flight levels (238 and 262 hPa); RHi stays close to constant with respect to SST for 238 hPa but shows an increasing trend for the 262-hPa level. Analysis conducted in this study represents a unique observational basis against which model simulations of upper-tropospheric humidity and its connection to deep convection and SST can be evaluated.

Ocean–atmosphere dynamics during Hurricane Ida and Nor’Ida: An application of the coupled ocean–atmosphere–wave–sediment transport (COAWST) modeling system

The coupled ocean–atmosphere–wave–sediment transport (COAWST) modeling system was used to investigate atmosphere–ocean–wave interactions in November 2009 during Hurricane Ida and its subsequent evolution to Nor’Ida, which was one of the most costly storm systems of the past two decades. One interesting aspect of this event is that it included two unique atmospheric extreme conditions, a hurricane and a nor’easter storm, which developed in regions with different oceanographic characteristics. Our modeled results were compared with several data sources, including GOES satellite infrared data, JASON-1 and JASON-2 altimeter data, CODAR measurements, and wave and tidal information from the National Data Buoy Center (NDBC) and the National Tidal Database. By performing a series of numerical runs, we were able to isolate the effect of the interaction terms between the atmosphere (modeled with Weather Research and Forecasting, the WRF model), the ocean (modeled with Regional Ocean Modeling System (ROMS)), and the wave propagation and generation model (modeled with Simulating Waves Nearshore (SWAN)). Special attention was given to the role of the ocean surface roughness. Three different ocean roughness closure models were analyzed: DGHQ (which is based on wave age), TY2001 (which is based on wave steepness), and OOST (which considers both the effects of wave age and steepness). Including the ocean roughness in the atmospheric module improved the wind intensity estimation and therefore also the wind waves, surface currents, and storm surge amplitude. For example, during the passage of Hurricane Ida through the Gulf of Mexico, the wind speeds were reduced due to wave-induced ocean roughness, resulting in better agreement with the measured winds. During Nor’Ida, including the wave-induced surface roughness changed the form and dimension of the main low pressure cell, affecting the intensity and direction of the winds. The combined wave age- and wave steepness-based parameterization (OOST) provided the best results for wind and wave growth prediction. However, the best agreement between the measured (CODAR) and computed surface currents and storm surge values was obtained with the wave steepness-based roughness parameterization (TY2001), although the differences obtained with respect to DGHQ were not significant. The influence of sea surface temperature (SST) fields on the atmospheric boundary layer dynamics was examined; in particular, we evaluated how the SST affects wind wave generation, surface currents and storm surges. The integrated hydrograph and integrated wave height, parameters that are highly correlated with the storm damage potential, were found to be highly sensitive to the ocean surface roughness parameterization.

Climatic Feedbacks during the 2003 European Heat Wave

Abstract During the summer of 2003, a record heat wave over Europe occurred, to which the deaths of over 20 000 people in 18 countries were attributed, 10 000 of those in France alone. Temperatures across Europe were above normal for most of the summer, but reached their peak during the first two weeks of August, when most of the deaths occurred. Ensemble simulations done with a recent version of the Center for Ocean–Land–Atmosphere Studies (COLA) atmospheric general circulation model (AGCM) have been analyzed over the European region. The simulations were forced by weekly mean observed sea surface temperature (SST). Relative to the 1982–2001 period, the COLA AGCM simulated anomalous warmth over the European region during June–August 2003, in response to the observed SST; however, the simulated magnitude was smaller than that observed. A series of simulations in which the observed SST was used only south of 25°N or only north of 25°N suggest that it was the influence of the local SST rather than remote SST that was an important influence on the heat wave. By early June, the soil over much of the European region was anomalously dry, consistent with the below-normal precipitation observed over the region in the preceding months. The model was restarted in early June with observation-based soil wetness anomalies imposed on the soil wetness from the control simulations. Although the model soil wetness was then allowed to evolve as usual, the simulations with the imposed initial soil wetness anomaly enhanced the simulated surface temperature anomaly during June–August by 1°–2°C. This weaker-than-observed temperature anomaly may be related to the persistence of imposed soil wetness anomalies, which was weaker than that observed. The experiments suggest that both the warm local SST and the dry local soil were important in intensifying the 2003 European heat wave.

Indices of trends of climatic changes for the states of the Bahia and Sergipe by means of daily precipitacion indices and its relation with SST'S of the Pacific and Atlantic

The objective of this study was to investigate statistically the precipitation variability in annual scale from the states of the Bahia and Sergipe using daily precipitation data. From that, indexes of detection of climate changes were calculated to evaluate the relationship of the most significant indexes with the sea surface temperature (SST) anomalies of the Pacific and Atlantic oceans. The daily precipitation data used were for a period of 45 years of 75 meteorological stations supplied by the old net of the SUDENE available in the DSA and data of the of the SST anomalies obtained from NOAA. Influence of SST of the Pacific and Atlantic oceans on the precipitation of the studied area is evidenced. A decrease of CWD was verified; increase was observed in the number days with rain; therefore, the amount of annual total precipitation increased. Several stations presented positive or negative tendencies in all examined indexes, consequently, they are also related to regional aspects. Therefore, it is not possible to affirm that the climate alterations noted in the study area are due to the global climate changes.

Spatio‐temporal metamodeling for West African monsoon

In this paper, we propose a new approach for modeling and fitting high‐dimensional response regression models in the setting of complex spatio‐temporal dynamics. This study is motivated by investigating one of the major atmospheric phenomena, which drives the rainfall regime in Western Africa: West African Monsoon. We are particularly interested in studying the influence of sea surface temperatures in the Gulf of Guinea on precipitation in Saharan and sub‐Saharan. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Deep Atmospheric Response to the Spring Kuroshio over the East China Sea*

AbstractThe atmospheric response to the spring Kuroshio Front over the East China Sea is investigated using a suite of high-resolution satellite data and a regional atmospheric model. The atmospheric response appears to extend beyond the marine atmospheric boundary layer, with frequent occurrence of cumulus convection.In spring, Quick Scatterometer (QuikSCAT) wind speed shows a clear effect of sea surface temperature (SST), with high (low) wind speed observed over the warm (cold) tongue. This in-phase relationship between SST and surface wind speed is indicative of SST influence on the atmosphere. Wind convergence is found on the warmer flank of the Kuroshio Front, accompanied by a narrow rainband. The analysis of satellite-borne radar measurements indicates that deep convection appears over the Kuroshio warm tongue in the spring season, with enhanced convective precipitation, frequent occurrence of cumulus convection, and increased precipitation (cloud) tops in altitude. These deep convective activities along the Kuroshio warm tongue are further supported by enhanced lightning flash rate observed by satellite and atmospheric heating estimated by a Japanese reanalysis.The Weather Research and Forecasting (WRF) model is used to investigate the precipitation response to the spring Kuroshio SST front over the East China Sea. Forced by observed SST [control (CTL)], the model well simulates a narrow band of precipitation, high wind speed, and surface wind convergence that closely follows the Kuroshio warm current, consistent with satellite observations. This narrow rainband completely disappears in the model when the SST front is removed by horizontally smoothed SST (SmSST). The results show that it is convective precipitation that is sensitive to the Kuroshio SST front. A case study for an eastward-moving extratropical cyclone indicates that convective precipitation increases its intensity and duration in the CTL run compared to the SmSST run. Local enhancement of upward sensible and latent heat fluxes and convective instability in the lower atmosphere are the key to anchoring the narrow band of convective precipitation that closely follows the Kuroshio.

Influence of sea surface temperature on the intraseasonal variability of the South China Sea summer monsoon

The objective of this study is to examine, based on recently available high resolution satellite and observational data, the evolution and role of sea surface temperature (SST) in influencing the intraseasonal variability of the South China Sea (SCS) summer monsoon (SM). The study focuses on the 30–60 day timescale when the northward propagating anomalies are dominant over the SCS. Composite analysis of the SST maximum events during SCS SM shows that increased SST anomalies over the SCS are significantly influenced by the downward shortwave radiation flux anomalies, with the suppressed surface latent heat flux anomalies supplementing to it. A thermal damping of the positive SST anomalies induces positive upward heat fluxes, which then destabilize the lower atmosphere between 1,000 and 700 hPa. The positive SST anomalies lead the positive precipitation anomalies over the SCS by 10 days, with a significant correlation (r = 0.44) between the SST-precipitation anomalies. The new findings here indicate an ocean-to-atmosphere effect over the SCS, where underlying SST anomalies tend to form a favorable condition for convective activity and sustain enhanced precipitation during the SCS SM. It is also argued, based on our observations, that the negative sea level pressure anomalies induced by the positive SST anomalies play a role in enhancing the northward propagation of the intraseasonal anomalies over the SCS.

Meteorological influences of SST anomaly over the East Asian marginal sea on subpolar and polar regions: A case of an extratropical cyclone on 5–8 November 2006

The eddy-resolving Japan Sea (East Sea) data assimilation affects the mid-level troposphere via vertical wind in the early stage of an explosively developing extratropical cyclone on 5–8 November 2006, and its influence further propagates toward the subpolar and polar regions. Two types of atmospheric responses (convective and gravity-wave patterns) to a sea surface temperature (SST) difference resulting from the ocean data assimilation are found in the early stage of the cyclone development over the western and central Japan Sea. A gravity-wave (convective) pattern appears when the near-surface atmosphere is stable (unstable). The atmospheric signals induced by the SST anomaly resulting from assimilation of the ocean circulation model are subject to advection and can deform with time owing to nonlinearity and instability. The differences in atmospheric and surface temperatures are widely and rapidly spread over the polar region by strong synoptic-scale cyclonic advection. On the other hand, the SST effects on vertical flow and precipitation are limited to narrow areas around the northern Japan Sea and the Pacific cold front in the fully developed stage. Such a developing cyclone is potentially important as a transporter of the meteorological influence over the Japan Sea toward the polar region.

Predictability of the spring rainfall in Northwestern Iberian Peninsula from sea surfaces temperature of ENSO areas

The influence of sea surface temperature (SST) of the ocean on seasonal rainfall in Northwestern Iberian Peninsula is studied for the period 1951–2006. Seasonal correlations were calculated for all seasons and different lags applied on SST. A test for field-significance considering the properties of finiteness and interdependence of the spatial grid was applied to avoid correlations by chance. The most significant and repetitive correlation is found between SST over Equatorial Pacific and spring rainfall. The correlation is maintained for different lags, and the common area that satisfies the criteria for statistical field significance is coincident with ENSO area. A forecast scheme is developed to predict spring rainfall anomalies based in SST over ENSO area in precedent seasons. An analysis of principal components was also carried out to obtain the main modes of the Pacific Ocean and their influence on spring rainfall in NWIP. This study concludes that for the period 1951–2006 the negative phase of ENSO, “La Nina”, almost always announces dry springs in NW Iberian Peninsula. However, the positive phase of ENSO, “El Nino”, does not anticipate the appearance of wet springs.

Coupled Ocean-Atmosphere Interaction at Oceanic Mesoscales

Satellite observations have revealed a remarkably strong positive correlation between sea-surface temperature (SST) and surface winds on oceanic mesoscales of 10-1000 km. While this SST influence on the atmosphere had previously been identified from several in situ observational studies, its widespread existence in regions of strong SST gradients throughout the World Ocean and the detailed structure of the surface wind response to SST have only become evident over the past decade from simultaneous satellite measurements of SST and surface winds. This has stimulated considerable scientific interest in the implications of this air-sea interaction to the large-scale and mesoscale circulation of the atmosphere and ocean. Convergence and divergence of surface winds in regions of spatially varying SST generate vertical motion that can penetrate deep into the atmosphere. Spatial variability of the SST field also results in a curl of the wind stress and its associated upwelling and downwelling that feeds back on the ocean and alters the SST itself. Significant progress has been made toward

Influences of Tidal Fronts on Coastal Winds Over an Inland Sea

A regional numerical model of the atmosphere was applied to an inland sea, the Seto Inland Sea in Japan, to study the influence of sea-surface temperature (SST) variations, accompanied by a tidal front, on the coastal winds in summer when tidal fronts fully develop. After confirmation of the model performance, two sensitivity simulations, which used spatially uniform SST with the highest and lowest values over the study area, were performed. The control and sensitivity simulations show that the mean wind speeds were apparently reduced by the low SST and the SST gradient accompanying the tidal front. The comparison of the terms in the momentum equations in control and sensitivity simulations indicates that the change of the perturbation pressure gradient force with the SST gradient is the most important factor in the modification of near-surface winds with SST variations. When the air flows across a tidal front, the air cools over the low SST area and warms over the high SST area. Consequently, the surface perturbation pressure increases over the low SST area and decreases over the high SST area. This adjustment in surface perturbation pressure produces an additional pressure gradient force with direction from the low SST area to the high SST area that decelerates the surface wind in the area upwind of the tidal front and accelerates the surface wind downwind of the tidal front.