Midsummer Gap Winds and Low-Level Circulation over the Eastern Tropical Pacific

2007 ◽  
Vol 20 (15) ◽  
pp. 3768-3784 ◽  
Author(s):  
Rosario Romero-Centeno ◽  
Jorge Zavala-Hidalgo ◽  
G. B. Raga
Keyword(s):  
Circulation Pattern ◽  
Early Spring ◽  
Tropical Pacific ◽  
Eastern Region ◽  
Southern Mexico ◽  
Trade Winds ◽  
Low Level ◽  
Western Caribbean ◽  
Gap Winds ◽  
Area Of Influence

Abstract The low-level seasonal and intraseasonal wind variability over the northeastern tropical Pacific (NETP), its relationship with other variables, and the connection with large- and middle-scale atmospheric patterns are analyzed using a suite of datasets. Quick Scatterometer (QuikSCAT) wind data show that the low-level circulation over the NETP is mainly affected by the northerly trades, the southerly trades, and the wind jets crossing through the Tehuantepec, Papagayo, and Panama mountain gaps. The seasonal and intraseasonal evolution of these wind systems determines the circulation patterns over the NETP, showing predominant easterly winds in winter and early spring and wind direction reversals in summer over the central region of the NETP. During summer, when southerly trades are the strongest and reach their maximum northward penetration, weak westerlies are observed in June, easterlies in July–August, despite that strong southerlies tend to turn eastward, and again westerlies in September–October. This circulation pattern appears to be related to the Tehuantepec and Papagayo jets, which slightly strengthen during midsummer favored by the westward elongation and intensification of the Azores–Bermuda high (ABH). This ABH evolution induces an across-gap pressure gradient over the Isthmus of Tehuantepec favoring the generation of the jet and a meridional sea level pressure (SLP) gradient in the western Caribbean that favors the funneling of the trade winds through the Papagayo gap. The SLP pattern causing the gap winds in winter is different than in midsummer, being the southeastward intrusion of high pressure systems coming from the northwest, the main cause of the large meridional SLP gradients in Tehuantepec and the western Caribbean. The westward low-level circulation observed over the central-eastern region of the NETP during midsummer induces westward moisture fluxes in the lower layers of the atmosphere, displaces convergence areas away from the coasts, and confines the relatively strong convergence in the easternmost NETP to the south of the area of influence of the wind jets and associated easterlies, contributing to the development of the midsummer drought observed in southern Mexico and Central America.

scholarly journals The Role of Tropical Interbasin SST Gradients in Forcing Walker Circulation Trends

2017 ◽  
Vol 30 (2) ◽  
pp. 499-508 ◽  
Author(s):  
Lei Zhang ◽  
Kristopher B. Karnauskas
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Walker Circulation ◽  
Equatorial Pacific ◽  
Trade Winds ◽  
Low Level ◽  
The Pacific ◽  
Indian Ocean Warming ◽  
Tropical Sea ◽  
Sst Gradient

The effects of externally forced tropical sea surface temperature (SST) anomalies on long-term Walker circulation changes are investigated through numerical atmospheric general circulation model (AGCM) experiments. In response to the observed tropics-wide SST trend, which exhibits a prominent interbasin warming contrast (IBWC) with smaller warming in the Pacific than the Indian and Atlantic Oceans that includes a weak La Niña–like pattern in the equatorial Pacific, pronounced low-level easterly anomalies emerge over the equatorial Pacific. Through sensitivity experiments, the intensification of the Pacific trade winds (PTWs) is attributable to the IBWC, whereas the slightly enhanced zonal SST gradient within the equatorial Pacific plays a small role relative to the observed IBWC. It is further demonstrated that the greater Indian Ocean warming forces low-level easterly anomalies over the entire equatorial Pacific, while the greater tropical Atlantic warming-driven enhancement of PTWs is located over the central equatorial Pacific. In contrast to observations, a negligible IBWC emerges in the tropical SST trends of CMIP5 historical simulations due to a strong El Niño–like warming in the tropical Pacific. Lacking the observed IBWC (and the observed enhancement of the zonal SST gradient within the equatorial Pacific), the PTWs in the CMIP5 ensemble can only weaken.

scholarly journals Strengthening of the Pacific Equatorial Undercurrent in the SODA Reanalysis: Mechanisms, Ocean Dynamics, and Implications

2014 ◽  
Vol 27 (6) ◽  
pp. 2405-2416 ◽  
Author(s):  
Elizabeth J. Drenkard ◽  
Kristopher B. Karnauskas
Keyword(s):  
Heat Budget ◽  
Tropical Pacific ◽  
Global Climate Models ◽  
Ocean Dynamics ◽  
Eastern Pacific ◽  
Boreal Summer ◽  
Trade Winds ◽  
Equatorial Undercurrent ◽  
The Pacific ◽  
The Tropical Pacific

Abstract Several recent studies utilizing global climate models predict that the Pacific Equatorial Undercurrent (EUC) will strengthen over the twenty-first century. Here, historical changes in the tropical Pacific are investigated using the Simple Ocean Data Assimilation (SODA) reanalysis toward understanding the dynamics and mechanisms that may dictate such a change. Although SODA does not assimilate velocity observations, the seasonal-to-interannual variability of the EUC estimated by SODA corresponds well with moored observations over a ~20-yr common period. Long-term trends in SODA indicate that the EUC core velocity has increased by 16% century−1 and as much as 47% century−1 at fixed locations since the mid-1800s. Diagnosis of the zonal momentum budget in the equatorial Pacific reveals two distinct seasonal mechanisms that explain the EUC strengthening. The first is characterized by strengthening of the western Pacific trade winds and hence oceanic zonal pressure gradient during boreal spring. The second entails weakening of eastern Pacific trade winds during boreal summer, which weakens the surface current and reduces EUC deceleration through vertical friction. EUC strengthening has important ecological implications as upwelling affects the thermal and biogeochemical environment. Furthermore, given the potential large-scale influence of EUC strength and depth on the heat budget in the eastern Pacific, the seasonal strengthening of the EUC may help reconcile paradoxical observations of Walker circulation slowdown and zonal SST gradient strengthening. Such a process would represent a new dynamical “thermostat” on CO2-forced warming of the tropical Pacific Ocean, emphasizing the importance of ocean dynamics and seasonality in understanding climate change projections.

High-frequency response of the ocean to mountain gap winds in the northeastern tropical Pacific

2009 ◽  
Vol 114 (C12) ◽  
Author(s):  
Jun-Hong Liang ◽  
James C. McWilliams ◽  
Nicolas Gruber
Keyword(s):  
Frequency Response ◽  
High Frequency ◽  
Tropical Pacific ◽  
High Frequency Response ◽  
Gap Winds

scholarly journals Low-Frequency Variability and Remote Forcing of Gap Winds over the East Pacific Warm Pool

2008 ◽  
Vol 21 (19) ◽  
pp. 4901-4918 ◽  
Author(s):  
Kristopher B. Karnauskas ◽  
Antonio J. Busalacchi ◽  
Raghu Murtugudde
Keyword(s):  
Wind Stress ◽  
Large Scale ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Warm Pool ◽  
Secondary Importance ◽  
Remote Forcing ◽  
Low Frequency Variability ◽  
Western Caribbean ◽  
Gap Winds

Abstract The low-frequency variability of gap winds at the Isthmuses of Tehuantepec and Papagayo is investigated using a 17-yr wind stress dataset merging the remotely sensed observations of Special Sensor Microwave Imager (SSM/I) and Quick Scatterometer (QuikSCAT) satellite sensors. A decadal signal is identified in the Tehuantepec gap winds, which is shown to be related to the Atlantic tripole pattern (ATP). Using linear regression and spectral analysis, it is demonstrated that the low-frequency variability of the Tehuantepec gap winds is remotely forced by the ATP, and the Papagayo gap winds are primarily governed by El Niño–Southern Oscillation (ENSO) with the ATP being of secondary importance. The Tehuantepec (Papagayo) time series of wind stress anomalies can be better reconstructed when the local cross-isthmus pressure difference and large-scale climate information such as the ATP (ENSO) are included, suggesting that there is important information in the large-scale flow that is not transmitted directly through the background sea level pressure gradient. The geostrophic modulation of the easterly trades in the western Caribbean also serve as a remote driver of the Papagayo gap winds, which is itself not fully independent from ENSO. Finally, it is suggested that precipitation variability in the Inter-Americas region is closely related to the same remote forcing as that of the Tehuantepec gap winds, being the ATP and associated large-scale atmospheric circulation.

scholarly journals The easternmost tropical Pacific. Part II: Seasonal and intraseasonal modes of atmospheric variability

2016 ◽  
Vol 64 (1) ◽  
pp. 23 ◽  
Author(s):  
Jorge A. Amador ◽  
A. M. Durán-Quesada ◽  
E. R. Rivera ◽  
G. Mora ◽  
F. Sáenz ◽  
...  
Keyword(s):  
Climate Variability ◽  
Moisture Transport ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Transport Processes ◽  
Seasonal Migration ◽  
World Heritage Site ◽  
Summer Drought ◽  
Low Level ◽  
The Caribbean

<p>This is Part II of a two-part review about climate and climate variability focused on the Eastern Tropical Pacific (ETP) and the Caribbean Sea (CS). Both parts are aimed at providing oceanographers, marine biologists, and other ocean scientists, a guiding base for ocean-atmosphere interaction processes affecting the CS, the ETP, and the waters of Isla del Coco. Isla del Coco National Park is a Costa Rican World Heritage site. Part I analyzed the mean fields for both basins and a larger region covering 25º S - 35º N, 20º W - 130º W. Here we focus on a smaller area (65º W - 95º W, 0º - 20º N), as a complement to Part 1. Incoming solar radiation and surface energy fluxes reveal the complex nature of the ETP and CS for convective activity and precipitation on seasonal and intraseasonal time scales. Both regions are relevant as sources of evaporation and the associated moisture transport processes. The American Monsoon System influences the climate and climate variability of the ETP and CS, however, the precise way systems affect regional precipitation and transport of moisture, within the Intra Americas Sea (IAS) are not clear. Although the Caribbean Low-Level Jet (CLLJ) is known to act as a conveyor belt for moisture transport, intraseasonal and seasonal modes of the CLLJ and their interactions with other IAS systems, have to be further investigated. Trans-isthmic jets, exert a variable seasonal wind stress force over the ocean surface co-generating regions of great marine productivity. Isolated convection, the seasonal migration of the Intertropical Convergence Zone, the hurricane season, the Mid-Summer Drought, the seasonal and intraseasonal behavior of low-level jets and their interactions with transients, and the southward incursion of cold fronts contribute to regional seasonal precipitation. Many large-scale systems, such as El Niño-Southern Oscillation, the Atlantic Multidecadal Oscillation and the Madden-Julian Oscillation (MJO, also influence the variability of precipitation by modulating regional features associated with convection and precipitation. Monthly tropical storm (TS) activity in the CS and ETP basins is restricted to the period May-November, with very few cases in December. The CS presents TS peak activity during August, as well as for the number of hurricanes and major hurricanes, in contrast to the ETP that shows the same features during September.</p><div> </div>

scholarly journals Evidence of eddy-related deep-ocean current variability in the northeast tropical Pacific Ocean induced by remote gap winds

2020 ◽  
Vol 17 (24) ◽  
pp. 6527-6544
Author(s):  
Kaveh Purkiani ◽  
André Paul ◽  
Annemiek Vink ◽  
Maren Walter ◽  
Michael Schulz ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Deep Sea ◽  
Seasonal Variability ◽  
Mesoscale Eddies ◽  
Deep Ocean ◽  
Tropical Pacific ◽  
Ocean Current ◽  
Tropical Pacific Ocean ◽  
Gap Winds ◽  
Anticyclonic Eddies

Abstract. There has been a steady increase in interest in mining of deep-sea minerals in the Clarion–Clipperton Zone (CCZ) in the eastern Pacific Ocean during the last decade. This region is known to be one of the most eddy-rich regions in the world ocean. Typically, mesoscale eddies are generated by intense wind bursts channeled through gaps in the Sierra Madre mountains in Central America. Here, we use a combination of satellite and in situ observations to evaluate the relationship between deep-sea current variability in the region of potential future mining and eddy kinetic energy (EKE) in the vicinity of gap winds. A geometry-based eddy detection algorithm has been applied to altimetry sea surface height data for a period of 24 years, from 1993 to 2016, in order to analyze the main characteristic parameters and the spatiotemporal variability of mesoscale eddies in the northeast tropical Pacific Ocean (NETP). Significant differences between the characteristics of eddies with different polarity (cyclonic vs. anticyclonic) were found. For eddies with lifetimes longer than 1 d, cyclonic polarity is more common than anticyclonic rotation. However, anticyclonic eddies are larger in size, show stronger vorticity, and survive longer in the ocean than cyclonic eddies (often 90 d or more). Besides the polarity of eddies, the location of eddy formation should be taken into consideration when investigating the impacted deep-ocean region as we found eddies originating from the Tehuantepec (TT) gap winds lasting longer in the ocean and traveling farther distances in a different direction compared to eddies produced by the Papagayo (PP) gap winds. Long-lived anticyclonic eddies generated by the TT gap winds are observed to travel distances up to 4500 km offshore, i.e., as far as west of 110∘ W. EKE anomalies observed in the surface of the central ocean at distances of ca. 2500 km from the coast correlate with the seasonal variability of EKE in the region of the TT gap winds with a time lag of 5–6 months. A significant seasonal variability of deep-ocean current velocities at water depths of 4100 m was observed in multiple-year time series data, likely reflecting the energy transfer of the surface EKE generated by the gap winds to the deep ocean. Furthermore, the influence of mesoscale eddies on deep-ocean currents is examined by analyzing the deep-ocean current measurements when an anticyclonic eddy crosses the study region. Our findings suggest that despite the significant modulation of dominant current directions driven by the bottom-reaching eddy, the current magnitude intensification was not strong enough to trigger local sediment resuspension in this region. A better insight into the annual variability of ocean surface mesoscale activity in the CCZ and its effects on deep-ocean current variability can be of great help to mitigate the impact of future potential deep-sea mining activities on the benthic ecosystem. On an interannual scale, a significant relationship between cyclonic eddy characteristics and El Niño–Southern Oscillation (ENSO) was found, whereas a weaker correlation was detected for anticyclonic eddies.

scholarly journals Improved ice content, radiation, precipitation and low-level circulation over the tropical pacific from ECMWF ERA-interim to ERA5

2021 ◽  
Author(s):  
Juilin Li ◽  
Kuan-Man Xu ◽  
Mark Richardson ◽  
Jonathan H Jiang ◽  
Graeme Stephens ◽  
...  
Keyword(s):  
Tropical Pacific ◽  
Low Level ◽  
Ice Content ◽  
The Tropical Pacific

Understanding the Anthropogenically Forced Change of Equatorial Pacific Trade Winds in Coupled Climate Models*

2014 ◽  
Vol 27 (22) ◽  
pp. 8510-8526 ◽  
Author(s):  
Baoqiang Xiang ◽  
Bin Wang ◽  
Juan Li ◽  
Ming Zhao ◽  
June-Yi Lee
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Climate Models ◽  
Walker Circulation ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Trade Wind ◽  
Trade Winds ◽  
The Walker Circulation

Abstract Understanding the change of equatorial Pacific trade winds is pivotal for understanding the global mean temperature change and the El Niño–Southern Oscillation (ENSO) property change. The weakening of the Walker circulation due to anthropogenic greenhouse gas (GHG) forcing was suggested as one of the most robust phenomena in current climate models by examining zonal sea level pressure gradient over the tropical Pacific. This study explores another component of the Walker circulation change focusing on equatorial Pacific trade wind change. Model sensitivity experiments demonstrate that the direct/fast response due to GHG forcing is to increase the trade winds, especially over the equatorial central-western Pacific (ECWP) (5°S–5°N, 140°E–150°W), while the indirect/slow response associated with sea surface temperature (SST) warming weakens the trade winds. Further, analysis of the results from 19 models in phase 5 of the Coupled Model Intercomparison Project (CMIP5) and the Parallel Ocean Program (POP)–Ocean Atmosphere Sea Ice Soil (OASIS)–ECHAM model (POEM) shows that the projected weakening of the trades is robust only in the equatorial eastern Pacific (EEP) ( 5°S–5°N, 150°–80°W), but highly uncertain over the ECWP with 9 out of 19 CMIP5 models producing intensified trades. The prominent and robust weakening of EEP trades is suggested to be mainly driven by a top-down mechanism: the mean vertical advection of more upper-tropospheric warming downward to generate a cyclonic circulation anomaly in the southeast tropical Pacific. In the ECWP, the large intermodel spread is primarily linked to model diversity in simulating the relative warming of the equatorial Pacific versus the tropical mean sea surface temperature. The possible root causes of the uncertainty for the trade wind change are also discussed.

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