Decadal Variability of the Indo-Pacific Warm Pool and Its Association with Atmospheric and Oceanic Variability in the NCEP–NCAR and SODA Reanalyses

2008 ◽  
Vol 21 (21) ◽  
pp. 5545-5565 ◽  
Author(s):  
Hui Wang ◽  
Vikram M. Mehta
Keyword(s):  
Decadal Variability ◽  
Gulf Coast ◽  
Phase Relationship ◽  
Warm Pool ◽  
The United States ◽  
Function Technique ◽  
Pacific Warm Pool ◽  
Rainfall Anomalies ◽  
Upper Level ◽  
Sst Anomalies

Abstract Decadal variability of the Indo-Pacific warm pool (IPWP) sea surface temperature (SST) and its association with atmospheric and oceanic circulations are investigated with observed 50-yr (1952–2001) SST, and the NCEP–NCAR atmospheric and Simple Ocean Data Assimilation (SODA) oceanic reanalysis data. The decadal variability of the IPWP SSTs was analyzed by applying an empirical orthogonal function technique to low-pass-filtered SSTs. Two leading empirical modes (EMs) well represent the IPWP SST decadal variations. EM1 is an ENSO-like pattern with out-of-phase SST anomalies in the western Pacific and the Indian Ocean, whereas EM2 displays an in-phase relationship between SST anomalies in the two regions. Consequently, spatial evolution of EM1 is dominated by opposing changes in zonal and meridional dimensions and thus a strong deformation of the warm pool on decadal time scales. EM2 is dominated by changes in size and intensity of the warm pool. Analyses of ocean thermodynamic fields associated with the two SST EMs indicate that decadal changes in the IPWP can extend down to 300-m depth. Oceanic processes may thus be involved in the IPWP decadal variability, including advections of mean temperature by both mean and anomalous ocean currents and effects of shallow tropical circulations (STCs) on the IPWP SST, which is consistent with some previous studies on tropical decadal variability. The results may also indicate the existence of both positive and negative feedbacks between the IPWP SST and the STCs. Both December–January–February (DJF) and June–July–August (JJA) atmospheric circulations exhibit thermally direct responses to the two decadal IPWP SST EMs by altering the Hadley and Walker circulations. In addition, significant upper-level rotational flow anomalies in the extratropics are found to be associated with the decadal IPWP SST variability. Consistent with the upper-level flow anomalies and 850-hPa convergence–divergence patterns associated with the two SST EMs are rainfall anomalies over the United States. In DJF, the rainfall anomalies are mainly in Florida, the Gulf Coast, southern Texas, Arizona, and along the West Coast. In JJA, the rainfall anomalies are mainly in the Midwest and the Southeast. Since these rainfall anomalies are a significant fraction of seasonal-average rainfall and since these anomalies persist for many years, they potentially make a significant impact on U.S. water resources and agriculture. Further analysis of observations and modeling studies are required to understand the physics of the IPWP SST decadal variability and its impacts on global climate, and to assess its predictability.

Subseasonal SST Variability in the Tropical Eastern North Pacific during Boreal Summer

2008 ◽  
Vol 21 (17) ◽  
pp. 4149-4167 ◽  
Author(s):  
Eric D. Maloney ◽  
Dudley B. Chelton ◽  
Steven K. Esbensen
Keyword(s):  
Costa Rica ◽  
Warm Pool ◽  
Boreal Summer ◽  
Sst Variability ◽  
East Pacific ◽  
Pacific Warm Pool ◽  
Northern Edge ◽  
Precipitation Anomalies ◽  
Sst Anomalies ◽  
Costa Rica Dome

Abstract Boreal summer intraseasonal (30–90-day time scale) sea surface temperature (SST) variability in the east Pacific warm pool is examined using Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) sea surface temperatures during 1998–2005. Intraseasonal SST variance maximizes at two locations in the warm pool: in the vicinity of 9°N, 92°W near the Costa Rica Dome and near the northern edge of the warm pool in the vicinity of 19°N, 108°W. Both locations exhibit a significant spectral peak at 50–60-day periods, time scales characteristic of the Madden–Julian oscillation (MJO). Complex empirical orthogonal function (CEOF) and spectra coherence analyses are used to show that boreal summer intraseasonal SST anomalies are coherent with precipitation anomalies across the east Pacific warm pool. Spatial variations of phase are modest across the warm pool, although evidence exists for the northward progression of intraseasonal SST and precipitation anomalies. Intraseasonal SSTs at the north edge of the warm pool lag those in the vicinity of the Costa Rica Dome by about 1 week. The MJO explains 30%–40% of the variance of intraseasonal SST anomalies in the east Pacific warm pool during boreal summer. Peak-to-peak SST variations of 0.8°–1.0°C occur during MJO events. SST is approximately in quadrature with MJO precipitation, with suppressed (enhanced) MJO precipitation anomalies leading positive (negative) SST anomalies by 7–10 days. Consistent with the CEOF and coherence analyses, MJO-related SST and precipitation anomalies near the Costa Rica Dome lead those at the northern edge of the warm pool by about 1 week.

scholarly journals Hurricane Katrina (2005). Part II: Evolution and Hemispheric Impacts of a Diabatically Generated Warm Pool

2007 ◽  
Vol 135 (12) ◽  
pp. 3927-3949 ◽  
Author(s):  
Ron McTaggart-Cowan ◽  
Lance F. Bosart ◽  
John R. Gyakum ◽  
Eyad H. Atallah
Keyword(s):  
United States ◽  
Hurricane Katrina ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Flow Analysis ◽  
Warm Pool ◽  
The United States ◽  
The North ◽  
The North Atlantic ◽  
Upper Level

Abstract The landfall of Hurricane Katrina (2005) near New Orleans, Louisiana, on 29 August 2005 will be remembered as one of the worst natural disasters in the history of the United States. By comparison, the extratropical transition (ET) of the system as it accelerates poleward over the following days is innocuous and the system weakens until its eventual demise off the coast of Greenland. The extent of Katrina’s perturbation of the midlatitude flow would appear to be limited given the lack of reintensification or downstream development during ET. However, the slow progression of a strong upper-tropospheric warm pool across the North Atlantic Ocean in the week following Katrina’s landfall prompts the question of whether even a nonreintensifying ET event can lead to significant modification of the midlatitude flow. Analysis of Hurricane Katrina’s outflow layer after landfall suggests that it does not itself make up the long-lived midlatitude warm pool. However, the interaction between Katrina’s anticyclonic outflow and an approaching baroclinic trough is shown to establish an anomalous southwesterly conduit or “freeway” that injects a preexisting tropospheric warm pool over the southwestern United States into the midlatitudes. This warm pool reduces predictability in medium-range forecasts over the North Atlantic and Europe while simultaneously aiding in the development of Hurricanes Maria and Nate. The origin of the warm pool is shown to be the combination of anticyclonic upper-level features generated by eastern Pacific Hurricane Hilary and the south Asian anticyclone (SAA). The hemispheric nature of the connections involved with the development of the warm pool and its injection into the extratropics has an impact on forecasting, since the predictability issue associated with ET in this case involves far more than the potential reintensification of the transitioning system itself.

How Many ENSO Flavors Can We Distinguish?*

2013 ◽  
Vol 26 (13) ◽  
pp. 4816-4827 ◽  
Author(s):  
Nathaniel C. Johnson
Keyword(s):  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
Tropical Pacific ◽  
La Niña ◽  
Western Pacific ◽  
Western Pacific Warm Pool ◽  
La Nina ◽  
Pacific Warm Pool ◽  
Sst Anomalies

Abstract It is now widely recognized that El Niño–Southern Oscillation (ENSO) occurs in more than one form, with the canonical eastern Pacific (EP) and more recently recognized central Pacific (CP) ENSO types receiving the most focus. Given that these various ENSO “flavors” may contribute to climate variability and long-term trends in unique ways, and that ENSO variability is not limited to these two types, this study presents a framework that treats ENSO as a continuum but determines a finite maximum number of statistically distinguishable representative ENSO patterns. A neural network–based cluster analysis called self-organizing map (SOM) analysis paired with a statistical distinguishability test determines nine unique patterns that characterize the September–February tropical Pacific SST anomaly fields for the period from 1950 through 2011. These nine patterns represent the flavors of ENSO, which include EP, CP, and mixed ENSO patterns. Over the 1950–2011 period, the most significant trends reflect changes in La Niña patterns, with a shift in dominance of La Niña–like patterns with weak or negative western Pacific warm pool SST anomalies until the mid-1970s, followed by a dominance of La Niña–like patterns with positive western Pacific warm pool SST anomalies, particularly after the mid-1990s. Both an EP and especially a CP El Niño pattern experienced positive frequency trends, but these trends are indistinguishable from natural variability. Overall, changes in frequency within the ENSO continuum contributed to the pattern of tropical Pacific warming, particularly in the equatorial eastern Pacific and especially in relation to changes of La Niña–like rather than El Niño–like patterns.

scholarly journals Modulation of the Meridional Structures of the Indo-Pacific Warm Pool on the Response of the Hadley Circulation to Tropical SST

2018 ◽  
Vol 31 (21) ◽  
pp. 8971-8984 ◽  
Author(s):  
Juan Feng ◽  
Jianping Li ◽  
Fred Kucharski ◽  
Yaqi Wang ◽  
Cheng Sun ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Hadley Circulation ◽  
Warm Pool ◽  
Sea Surface ◽  
Response Ratio ◽  
The Past ◽  
Pacific Warm Pool ◽  
Mean Sea Surface ◽  
Sst Anomalies

By decomposing the variations of the Hadley circulation (HC) and tropical zonal-mean sea surface temperature (SST) into the equatorially asymmetric (HEA for HC, SEA for SST) and symmetric (HES for HC, SES for SST) components, the varying response of the HC to different SST meridional structures under warm and cold conditions of the Indo-Pacific warm pool (IPWP) is investigated over the period 1979–2016. The response of the HC to SST evidences an asymmetric variation between warm and cold IPWP conditions; that is, the response ratio of HEA to SEA relative to that of HES to SES is ~5 under warm conditions and ~2 under cold conditions. This asymmetry is primarily due to a decrease in the HEA-to-SEA ratio under cold IPWP conditions, and is driven by changes in the meridional distribution of SST anomalies. Equatorial asymmetric (symmetric) SST anomalies are dominated by warm (cold) IPWP conditions. Thus, variations of SEA are suppressed under cold IPWP conditions, contributing to the observed weakening of the HEA-to-SEA ratio. The results presented here indicate that the HC is more sensitive to the underlying SST when the IPWP is warmer, during which the variation of SEA is enhanced, suggesting a recent strengthening of the response of the HC to SST, as the IPWP has warmed over the past several decades, and highlighting the importance of the IPWP meridional structures rather than the overall warming of the HC.

A Study of the Impact of Off-Equatorial Warm Pool SST Anomalies on ENSO Cycles

2005 ◽  
Vol 18 (2) ◽  
pp. 274-286 ◽  
Author(s):  
Amy Solomon ◽  
Fei-Fei Jin
Keyword(s):  
El Niño ◽  
El Nino ◽  
Coupled Model ◽  
Warm Pool ◽  
Western Pacific ◽  
Sea Surface ◽  
Pacific Warm Pool ◽  
The Impact ◽  
The Western Pacific ◽  
Sst Anomalies

Abstract Concurrent with most large El Niño events, cold sea surface temperature (SST) anomalies are observed over the western Pacific warm pool region (WPWP). Observational evidence that SST anomalies that form in the off-equatorial western Pacific during El Niño–Southern Oscillation (ENSO) cycles are forced by subsurface ocean processes equatorward of 12°N and air–sea fluxes poleward of 12°N is presented. It is demonstrated that diurnal mixing in the ocean equatorward of 12°N plays a significant role in bringing subsurface temperature anomalies to the sea surface during an El Niño event. The role of SST anomalies equatorward of 12°N in ENSO cycles is tested in the Zebiak–Cane coupled model, modified to allow for the impact of subsurface temperatures on SSTs. This coupled model successfully simulates cold SST anomalies in the off-equatorial northwestern Pacific that are observed to occur during the warm phase of ENSO and the atmospheric response to these anomalies, which is composed of both westerlies in the central Pacific and easterlies in the far western equatorial Pacific. It is found that there is little net change in the zonal mean wind stress at the equator, suggesting that the westerlies cancel the impact of the easterlies on the basin-scale tilt of the equatorial zonal mean thermocline depth. The anomalous westerly winds in the central equatorial Pacific are found to increase the amplitude of an El Niño event directly by increasing anomalous warm zonal advection and reducing upwelling. Moreover, the off-equatorial anticyclonic wind stress associated with the cold SST anomalies during the warm phase of ENSO tends to reduce the discharge of the equatorial heat content. Thus, the coupled processes over the western Pacific warm pool can serve as a positive feedback to amplify ENSO cycles.

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