Tropical Atmospheric Circulation Research Articles

In the hot seat: Insolation, ENSO, and vegetation in the African tropics

AbstractAfrican climate is changing at rates unprecedented in the Late Holocene with profound implications for tropical ecosystems and the global hydrologic cycle. Understanding the specific climate drivers behind tropical ecosystem change is critical for both future and paleomodeling efforts. However, linkages between climate and vegetation in the tropics have been extremely controversial. The Normalized Difference Vegetation Index (NDVI) is a satellite‐derived index of vegetation productivity with a high spatial and temporal resolution. Here we use regression analysis to show that NDVI variability in Africa is primarily correlated with the interannual extent of the Intertropical Convergence Zone (ITCZ). Our results indicate that interannual variability of the ITCZ, rather than sea surface temperatures or teleconnections to middle/high latitudes, drives patterns in African vegetation resulting from the effects of insolation anomalies and El Niño–Southern Oscillation (ENSO) events on atmospheric circulation. Global controls on tropical atmospheric circulation allow for spatially coherent reconstruction of interannual vegetation variability throughout Africa on many time scales through regulation of dry season length and moisture convergence, rather than precipitation amount.

Revealing the effects of the El Niño-southern oscillation on tropical cyclone intensity over the western north pacific from a model sensitivity study

Five sets of model sensitivity experiments are conducted to investigate the influence of tropical cyclone (TC) genesis location and atmospheric circulation on interannual variability of TC intensity in the western North Pacific (WNP). In each experiment, bogus TCs are placed at different initial locations, and simulations are conducted with identical initial and boundary conditions. In the first three experiments, the specified atmospheric and SST conditions represent the mean conditions of El Nio, La Nia, and neutral years. The other two experiments are conducted with the specified atmospheric conditions of El Nio and La Nia years but with SSTs exchanged. The model results suggest that TCs generated in the southeastern WNP incurred more favorable environmental conditions for development than TCs generated elsewhere. The different TC intensities between El Nio and La Nia years are caused by difference in TC genesis location and low-level vorticity (VOR). VOR plays a significant role in the intensities of TCs with the same genesis locations between El Nio and La Nia years.

Tropospheric biennial oscillation of the western Pacific subtropical high and its relationships with the tropical SST and atmospheric circulation anomalies

There is the significant period of tropospheric biennial Oscillation (TBO) over East Asian monsoon region at the interannual timescales, which has the important influences on East China climate. Based on a set of reconstructed indices which describes the western Pacific subtropical high (WPSH) objectively, this paper focuses on the TBO component of WPSH, one of the key members of the East Asian Monsoon system, and its relationships with the tropical SST and atmospheric circulation anomalies. It is found that (1) As an important interannual component of WPSH, the time series of TBO has the obvious transition in the late 1970s, and the variability of the WPSH’s TBO component is more significant after the late 1970s. (2) The time-lag correlations between the WPSH’s TBO and the tropical sea surface temperature (SST) anomalies in several key ocean regions are more significant and have longer correlation duration than the raw data. The response of the western boundary index to ENSO is earlier than the intensity index, and the time-lag correlations of them are up to maximum when lagging ENSO by 3–5 months and 5–6 months, respectively. (3) In the course of the WPSH’s TBO cycle, the occurrence of the El Nino-like anomaly in the tropical centraleastern Pacific in winter is always coupled with the weak East Asian winter monsoon, with the most significant enhancing phase of the WPSH’ TBO. In contrast, the La Nina-like anomaly in the central-eastern Pacific in winter is coupled with the strong East Asian winter monsoon, with the most weakening phase of the WPSH’s TBO. (4) The distribution of the tropical SST and atmospheric circulations anomalies are asymmetric in the TBO cycle. The WPSH’s TBO is more significant in the period of the developing El Nino-like anomaly in central-eastern Pacific than in the period of the developing La Nina-like anomaly. Therefore, during the period of developing El Nino-like anomaly, more attention should be paid to the interannual component of TBO signal in the short-term climate prediction.

Interdecadal enhancement of the walker circulation over the Tropical Pacific in the late 1990s

The Walker circulation is one of the major components of the large-scale tropical atmospheric circulation and variations in its strength are critical to equatorial Pacific Ocean circulation. It has been argued in the literature that during the 20th century the Walker circulation weakened, and that this weakening was attributable to anthropogenic climate change. By using updated observations, we show that there has been a rapid interdecadal enhancement of the Walker circulation since the late 1990s. Associated with this enhancement is enhanced precipitation in the tropical western Pacific, anomalous westerlies in the upper troposphere, descent in the central and eastern tropical Pacific, and anomalous surface easterlies in the western and central tropical Pacific. The characteristics of associated oceanic changes are a strengthened thermocline slope and an enhanced zonal SST gradient across the tropical Pacific. Many characteristics of these changes are similar to those associated with the mid-1970s climate shift with an opposite sign. We also show that the interdecadal variability of the Walker circulation in the tropical Pacific is inversely correlated to the interdecadal variability of the zonal circulation in the tropical Atlantic. An enhancement of the Walker circulation in the tropical Pacific is associated with a weakening zonal circulation in the tropical Atlantic and vise versa, implying an inter-Atlantic-Pacific connection of the zonal overturning circulation variation. Whether these recent changes will be sustained is not yet clear, but our research highlights the importance of understanding the interdecadal variability, as well as the long-term trends, that influence tropical circulation.

Zonal Momentum Balance in the Tropical Atmospheric Circulation during the Global Monsoon Mature Months

AbstractIn this paper, zonal momentum balances of the tropical atmospheric circulation during the global monsoon mature months (January and July) are analyzed in three dimensions based on the ECMWF Interim Re-Analysis (ERA-Interim). It is found that the dominant terms in the balance of the atmospheric boundary layer (ABL) in both months are the pressure gradient force, the Coriolis force, and friction. The nonlinear advection term plays a significant role only in the Asian summer monsoon regions within the ABL. In the upper troposphere, the pressure gradient force, the Coriolis force, and the nonlinear advection are the dominant terms. The transient eddy force and the residual force (which can be explained as convective momentum transfer over open oceans) are secondary, yet cannot be neglected near the equator. Zonal-mean equatorial upper-troposphere easterlies are maintained by the absolute angular momentum advection associated with the cross-equatorial Hadley circulation. Equatorial upper-troposphere easterlies over the Asian monsoon regions are also controlled by the absolute angular momentum advection but are mainly maintained by the pressure gradient force in January. The equivalent linear Rayleigh friction, which is widely applied in simple tropical models, is calculated and the corresponding spatial distribution of the local coefficient and damping time scale are estimated from the linear regression. It is found that the linear momentum model is in general capable of crudely describing the tropical atmospheric circulation dynamics, yet the caveat should be kept in mind that the friction coefficient is not uniformly distributed and is even negative in some regions.

An analysis on the physical process of the influence of AO on ENSO

The influence of the spring AO on ENSO has been demonstrated in several recent studies. This analysis further explores the physical process of the influence of AO on ENSO using the NCEP/NCAR reanalysis data over the period 1958–2010. We focus on the formation of the westerly wind burst in the tropical western Pacific, and examine the evolution and formation of the atmospheric circulation, atmospheric heating, and SST anomalies in association with the spring AO variability. The spring AO variability is found to be independent from the East Asian winter monsoon activity. The spring AO associated circulation anomalies are supported by the interaction between synoptic-scale eddies and the mean-flow and its associated vorticity transportation. Surface wind changes may affect surface heat fluxes and the oceanic heat transport, resulting in the SST change. The AO associated warming in the equatorial SSTs results primarily from the ocean heat transport in the face of net surface heat flux damping. The tropical SST warming is accompanied by anomalous atmospheric heating in the subtropical north and south Pacific, which sustains the anomalous westerly wind in the equatorial western Pacific through a Gill-like atmospheric response from spring to summer. The anomalous westerly excites an eastward propagating and downwelling equatorial Kelvin wave, leading to SST warming in the tropical central-eastern Pacific in summer-fall. The tropical SST, atmospheric heating, and atmospheric circulation anomalies sustain and develop through the Bjerknes feedback mechanism, which eventually result in an El Nino-like warming in the tropical eastern Pacific in winter.

Effect of SST Variation on ITCZ in APE Simulations

The effect of meridional variation of sea surface temperature (SST) on tropical atmospheric circulation is analyzed using Aqua-planet Experiment (APE) simulations. The meridional SST gradient around the narrow SST peak in CONTROL simulation favours a strong and single equatorial Intertropical Convergence Zone (ITCZ, defined by the maximum of zonally averaged total precipitation) in all APE models. In contrast, flat equatorial SST peak (FLAT simulation) favours split/double ITCZs flanking the SST maximum, in the majority of the APE models. Although there is reasonable agreement for SST sensitivity of ITCZ among the APE models in CONTROL, there exists disparity among them in FLAT case. Similarly, while the total and convective precipitation responses are consistent among the models, the large-scale precipitation response shows considerable inter-model variations in FLAT case. The APE intercomparison indicates that the occurrence and positioning of the ITCZ are primarily related to boundary layer moisture convergence as a response to the meridional variation of SST. Furthermore, the meridional gradient of tropospheric temperature is found to be an important factor that can influence the positioning of ITCZ. FLAT SST distribution is found to be similar to the observed distribution over the Indian region during summer season. Models that yield double ITCZs in this case simulate an easterly jet over the equatorial region (similar to 15 degrees equatorward of the ITCZ). This is analogous to the Tropical Easterly Jet (TEJ), which is a unique feature observed over the Indian region during summer monsoon season, with its core at 12 degrees N, equatorward of the seasonal convergence zone centered along 25 degrees N. In these models, positive meridional temperature gradient and the associated easterly shear in the atmosphere strengthened by moisture convergence penetrate up to the upper troposphere, with which TEJ is in thermal wind balance.

The Relationship of Rainfall Variability in Western Equatorial Africa to the Tropical Oceans and Atmospheric Circulation. Part II: The Boreal Autumn

Abstract This paper examines the mechanisms controlling the year-to-year variability of rainfall over western equatorial Africa during the rainy season of October–December. Five regions with distinct behavior are analyzed separately. Only two show strong associations with the ocean and atmospheric features in the global tropics. These two regions, in the east (the eastern Zaire basin) and west (Angolan coast) of the study area, respectively, demonstrate strikingly opposite relationships with the anomalies of sea surface temperatures (SSTs), sea level pressure (SLP), and east–west atmospheric circulation. The wet (dry) conditions in the eastern Zaire basin are associated with El Niño(La Niña)–like phases. The inverse pattern is apparent for the Angolan coast. The other three regions, lying between these two poles of variability, represent a transition zone with a weak linear relationship to the circulation features. The vital impact of the east–west circulation cells on rainfall variability results in a stronger association with zonal wind than with SSTs or SLP. In addition to the zonal shift, changes in intensity of the zonal cells also play a crucial role. Variability in both magnitude and location of the circulation cells appear to be modulated by the remote forcing from the Pacific via an atmospheric bridge. However, the eastern sector is impacted mainly when synchronous changes occur in the Indian Ocean, and the western sector is impacted mainly when synchronous changes occur in the Atlantic Ocean.

The Relationship of Rainfall Variability in Western Equatorial Africa to the Tropical Oceans and Atmospheric Circulation. Part I: The Boreal Spring

Abstract This paper examines the factors governing rainfall variability in western equatorial Africa (WEA) during the April–June rainy season. In three of the five regions examined some degree of large-scale forcing is indicated, particularly in the region along the Atlantic coast. Interannual variability in this coastal sector also demonstrates a strong link to changes in local sea surface temperatures (SSTs) and the South Atlantic subtropical high. To examine potential causal mechanisms, various atmospheric parameters are evaluated for wet and dry composites. The results suggest that the intensity of the zonal circulation in the global tropics is a crucial control on rainfall variability over WEA. A La Niña (El Niño)–like signal in both SSTs and zonal circulation over the Pacific is apparent in association with the wet (dry) conditions in the western sector. However, remote forcing from the Pacific modulates the circulation over Africa indirectly by way of synchronous changes in the entire Indian or Atlantic Ocean. Anomalies in the local zonal winds are similar in all three regions: the wet (dry) composite is associated with an intensification (weakening) of the upper-tropospheric easterlies and low-level westerlies, but a weakening (intensification) of the midlevel easterlies. This work also suggests that, in most cases, the relationship between local SSTs and rainfall reflects a common remote forcing by the large-scale atmosphere–ocean system. This forcing is manifested via changes in the zonal circulation. Thus, the statistical associations between rainfall and SSTs do not indicate direct forcing by local SSTs. One point of evidence for this conclusion is the stronger association with atmospheric parameters than with SSTs.

Different types of La Niña events and different responses of the tropical atmosphere

Historical La Nina events since 1950 are divided into Eastern Pacific (EP) type and Central Pacific (CP) type, and the SSTA developing features as well as the different responses of the tropical atmosphere are further analyzed by using multiple datasets. Classification of different types La Nina is based on the normalized Nino3 and Nino4 indices and the SSTA distribution pattern during the mature phase. The minimum negative SSTA for CP La Nina is located over the equatorial central Pacific near the dateline, more westward than that of EP La Nina. It has stronger intensity and larger east-west zonal difference of SSTA over the equatorial Pacific than EP La Nina. Influenced by the different SSTA distribution pattern, CP La Nina induces more westward location of the anomalous sinking motion and the anomalous low-level divergent and high-level convergent winds over the equatorial eastern Pacific. The different response of the tropical atmospheric circulation between EP and CP La Nina is more significant in the upper troposphere than in the lower troposphere. However, the tropical precipitation patterns during the mature phase of EP and CP La Nina are much similar, except the less (more) precipitation over the equatorial central Pacific (eastern Indian Ocean-western Pacific) during CP La Nina than during EP La Nina.

Solar forcing of Florida Straits surface salinity during the early Holocene

Previous studies showed that sea surface salinity (SSS) in the Florida Straits as well as Florida Current transport covaried with changes in North Atlantic climate over the past two millennia. However, little is known about earlier Holocene hydrographic variability in the Florida Straits. Here, we combine Mg/Ca‐paleothermometry and stable oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber (white variety) from Florida Straits sediment core KNR166–2 JPC 51 (24° 24.70′ N, 83° 13.14′ W, 198 m deep) to reconstruct a high‐resolution (∼25 yr/sample) early to mid Holocene record of sea surface temperature and δ18OSW (a proxy for SSS) variability. After removing the influence of global δ18OSW change due to continental ice volume variability, we find that early Holocene SSS enrichments are associated with increased evaporation/precipitation ratios in the Florida Straits during periods of reduced solar forcing, increased ice rafted debris in the North Atlantic and the development of more permanent El Niño–like conditions in the eastern equatorial Pacific. When considered with previous high‐resolution reconstructions of Holocene tropical atmospheric circulation changes, our results provide evidence that variations in solar forcing over the early Holocene had a significant impact on the global tropical hydrologic cycle.

High-Resolution Global Climate Simulations with the ECMWF Model in Project Athena: Experimental Design, Model Climate, and Seasonal Forecast Skill

The sensitivity to the horizontal resolution of the climate, anthropogenic climate change, and seasonal predictive skill of the ECMWF model has been studied as part of Project Athena—an international collaboration formed to test the hypothesis that substantial progress in simulating and predicting climate can be achieved if mesoscale and subsynoptic atmospheric phenomena are more realistically represented in climate models.In this study the experiments carried out with the ECMWF model (atmosphere only) are described in detail. Here, the focus is on the tropics and the Northern Hemisphere extratropics during boreal winter. The resolutions considered in Project Athena for the ECMWF model are T159 (126 km), T511 (39 km), T1279 (16 km), and T2047 (10 km). It was found that increasing horizontal resolution improves the tropical precipitation, the tropical atmospheric circulation, the frequency of occurrence of Euro-Atlantic blocking, and the representation of extratropical cyclones in large parts of the Northern Hemisphere extratropics. All of these improvements come from the increase in resolution from T159 to T511 with relatively small changes for further resolution increases to T1279 and T2047, although it should be noted that results from this very highest resolution are from a previously untested model version. Problems in simulating the Madden–Julian oscillation remain unchanged for all resolutions tested. There is some evidence that increasing horizontal resolution to T1279 leads to moderate increases in seasonal forecast skill during boreal winter in the tropics and Northern Hemisphere extratropics. Sensitivity experiments are discussed, which helps to foster a better understanding of some of the resolution dependence found for the ECMWF model in Project Athena.

TC-Permitting GCM Simulations of Hurricane Frequency Response to Sea Surface Temperature Anomalies Projected for the Late-Twenty-First Century

Abstract A tropical cyclone–permitting global atmospheric model is used to explore the hurricane frequency response to sea surface temperature (SST) anomalies generated by coupled models for the late-twenty-first century. Results are presented for SST anomalies averaged over 18 models as well as from 8 individual models. For each basin, there exists large intermodel spread in the magnitude and even the sign of the frequency response among the different SST projections. These sizable variations in response are explored to understand features of SST distributions that are important for the basin-wide hurricane responses. In the North Atlantic, the eastern Pacific, and the southern Indian basins, most (72%–86%) of the intermodel variance in storm frequency response can be explained by a simple relative SST index defined as a basin’s storm development region SST minus the tropical mean SST. The explained variance is significantly lower in the South Pacific (48%) and much lower in the western Pacific basin (27%). Several atmospheric parameters are utilized to probe changes in tropical atmospheric circulation and thermodynamical properties relevant to storm genesis in the model. While all present strong correlation to storm response in some basins, a parameter-measuring tropospheric convective mass flux stands out as skillful in explaining the simulated differences for all basins. Globally, in addition to a modest reduction of total storm frequency, the simulations exhibit a small, but robust eastward and poleward migration of genesis frequency in both the North Pacific and the North Atlantic Oceans. This eastward migration of storms can also be explained by changes in convection.

Hydroclimate variability and long-lead forecasting of rainfall over Thailand by large-scale atmospheric variables

The development of statistical relationships between local hydroclimates and large-scale atmospheric variables enhances the understanding of hydroclimate variability. The rainfall in the study basin (the Upper Chao Phraya River Basin, Thailand) is influenced by the Indian Ocean and tropical Pacific Ocean atmospheric circulation. Using correlation analysis and cross-validated multiple regression, the large-scale atmospheric variables, such as temperature, pressure and wind, over given regions are identified. The forecasting models using atmospheric predictors show the capability of long-lead forecasting. The modified k-nearest neighbour (k-nn) model, which is developed using the identified predictors to forecast rainfall, and evaluated by likelihood function, shows a long-lead forecast of monsoon rainfall at 7–9 months. The decreasing performance in forecasting dry-season rainfall is found for both short and long lead times. The developed model also presents better performance in forecasting pre-monsoon season rainfall in dry years compared to wet years, and vice versa for monsoon season rainfall. Editor Z.W. Kundzewicz Citation Singhrattna, N., Babel, M.S. and Perret, S.R., 2012. Hydroclimate variability and long-lead forecasting of rainfall over Thailand by large-scale atmospheric variables. Hydrological Sciences Journal, 57 (1), 26–41.

Florida Straits deglacial temperature and salinity change: Implications for tropical hydrologic cycle variability during the Younger Dryas

The prevailing paradigm of abrupt climate change holds that rapid shifts associated with the most extreme climate swings of the last glacial cycle were forced by changes in the strength and northward extension of Atlantic Meridional Overturning Circulation (AMOC), resulting in an abrupt reorganization of atmospheric circulation patterns with global teleconnections. To determine the timing of tropical Atlantic atmospheric circulation changes over the past 21 ka BP, we reconstruct high resolution sea surface temperature and δ18OSW (a proxy for surface salinity) records based on Mg/Ca ratios and oxygen isotope measurements in the planktonic foraminifera Globigerinoides ruber from a sediment core located on the western margin of the Florida Straits. As a proxy for meltwater discharge influence on Florida Straits surface water salinity, we also measured Ba/Ca ratios in G. ruber from the same core. Results show that riverine influence on Florida Straits surface water started by 17.2 ka BP and ended by 13.6 ka BP, 600 years before the start of the Younger Dryas (YD) cold interval. The initiation of the YD is marked by an abrupt increase in Florida Straits δ18OSW values, indicating a shift to elevated sea surface salinity occurring in 130 years, most likely resulting from increased regional aridity and/or reduced precipitation. In order to resolve the timing of tropical atmospheric circulation change relative to AMOC variability across this transition, we compare the timing of surface water changes to a recently published record of Florida Current variability in the same core reconstructed from benthic oxygen isotope measurements. We find synchronous changes in atmospheric and ocean circulation on the transition into the YD, consistent with an abrupt reduction in AMOC as the driver of tropical Atlantic atmospheric circulation change at this time.

Changes in water vapor transports of the ascending branch of the tropical circulation

[2] Recent and future changes in the statistical characteristics of the tropical atmospheric circulation (TAC) pattern and associated changes in the tropical hydrological cycle do not only locally affect the weather properties in the tropical areas but they have an influence on the extratropical regions. The general TAC pattern consists of convective regions of upward, ascending air movement (ASC) and of regions of downward, descending air motion (DESC), with low‐level flow into ASC and midlevel outflow into DESC commonly referred to as the Hadley Cell circulation. Along with the upward air motion, ASC contains most of the tropical precipitation and in its annual cycle by and large follows the Sun’s zenith. Part of the water vapor originates from evaporation in areas close by, but additionally large amounts of water are transported by atmospheric movements from DESC, causing a largely positive tropical water balance (precipitation‐evaporation) at the cost of the dry subtropics. A number of recent studies have addressed past and possible future changes in the moisture budget or in other components of the hydrological cycle over the tropics or over parts of the tropics. An increase in low‐level atmospheric water vapor of 7% per degree of warming is derived from theoretical considerations (Clausius‐Clapeyron relation, e.g., Wentz and Schabel[2000]; Trenberth et al. [2003]; Held and Soden

Forcing of the Indian Ocean Dipole on the Interannual Variations of the Tropical Pacific Ocean: Roles of the Indonesian Throughflow

Abstract Controlled numerical experiments using ocean-only and ocean–atmosphere coupled general circulation models show that interannual sea level depression in the eastern Indian Ocean during the Indian Ocean dipole (IOD) events forces enhanced Indonesian Throughflow (ITF) to transport warm water from the upper-equatorial Pacific Ocean to the Indian Ocean. The enhanced transport produces elevation of the thermocline and cold subsurface temperature anomalies in the western equatorial Pacific Ocean, which propagate to the eastern equatorial Pacific to induce significant coupled evolution of the tropical Pacific oceanic and atmospheric circulation. Analyses suggest that the IOD-forced ITF transport anomalies are about the same amplitudes as those induced by the Pacific ENSO. Results of the coupled model experiments suggest that the anomalies induced by the IOD persist in the equatorial Pacific until the year following the IOD event, suggesting the importance of the oceanic channel in modulating the interannual climate variations of the tropical Pacific Ocean at the time lag beyond one year.

Tropical atmospheric circulation and precipitation changing

As Earth's climate has warmed over the past several decades, atmospheric and hydrological cycle changes are being observed globally and regionally. For instance, Zhou et al. analyzed trends in the hydrological cycle in the tropics over the past 20–30 years using precipitation, cloud, and radiation data. In particular, the researchers looked at Hadley and Walker cell atmospheric circulation patterns. Hadley circulation is a major circulation pattern in the tropical atmosphere in which air masses, warmed by the Sun, rise near the equator, then travel poleward, sink back toward Earth's surface in the subtropics, and return to the equator. Similarly, in the Walker circulation, air rises over the warmer parts of the oceans near the equator, travels zonally toward the colder parts, then sinks back to the surface. There are indications that both of these circulation patterns are changing with global warming and could be altering precipitation and cloud radiation distributions in the tropical regions. (Journal of Geophysical Research‐Atmospheres, doi:10.1029/2010JD015197, 2011)

The Indian Ocean’s asymmetric effect on the coupling of the Northwest Pacific SST and anticyclone anomalies during its spring–summer transition after El Niño

By comparing different climatologies in El Nino decaying summer with regard to the presence of Indian Ocean Basin (IOB) warming, we studied the effect of IOB warming on the Northwest Pacific sea surface temperature (SST) anomalies and the coupling process with the surface wind. Zonal asymmetric coupling feedback in the west and east of the Northwest Pacific were caused by the asymmetric spring–summer transition of the background tropical atmospheric circulation. Although the westward wind anomaly caused by the remote effect of IOB warming is found in the whole Northwest Pacific, reversal of the mean background surface winds in the western part leads to negative wind-evaporation SST (WES), whereas sustained trade winds lead to positive WES in the eastern part. The east–west SST gradient resulting from this zonal asymmetric evolution of SST sets off more positive feedback that strengthens the local anticyclone easterly anomalies.

Evidence for strengthening of the tropical Pacific Ocean surface wind speed during 1979–2001

Using multiple surface wind speed (SWS) data sets and trend empirical orthogonal function analysis, we have explored the trend in SWS associated with the large-scale tropical Pacific atmospheric circulation for the period 1979–2001. The present research provides a robust evidence of strengthening of the tropical Pacific Ocean SWS during this period and the magnitude is generally in line with the finding of Wentz et al. The strengthening in SWS is closely associated with the so-called La Nina-like sea surface temperature (SST) trend pattern rather than the changes in the ENSO, ENSO Modoki, or PDO. The present results, together with those from some recent climate model simulations, suggest that global warming forcing may have caused an intensification of SWS in the tropical Pacific Ocean by inducing the La Nina-like SST trend pattern due to ocean dynamics. Meanwhile, the strengthening in the tropical Pacific Ocean surface trade winds may also feedback to enhance the La Nina-like SST trend pattern under the positive wind-upwelling dynamic feedback mechanism.