Meridional SST gradient in the western North Pacific warm pool associated with typhoon generation

2008 ◽  
Vol 35 (12) ◽  
pp. n/a-n/a ◽  
Author(s):  
N. Sato ◽  
R. Shirooka ◽  
M. Yoshizaki ◽  
Y. N. Takayabu
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Warm Pool ◽  
Pacific Warm Pool ◽  
Sst Gradient ◽  
Meridional Sst Gradient

Impacts of the Boreal Spring Indo-Pacific Warm Pool Hadley Circulation on Tropical Cyclone Activity over the Western North Pacific

2018 ◽  
Vol 31 (4) ◽  
pp. 1361-1375 ◽  
Author(s):  
Yi-Peng Guo ◽  
Zhe-Min Tan
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
Hadley Circulation ◽  
Warm Pool ◽  
Westerly Wind ◽  
Pacific Warm Pool ◽  
Sst Gradient

This study investigated the impacts of the interannual variability in the boreal spring regional Hadley circulation over the Indo-Pacific warm pool (IPWP) on the tropical cyclone (TC) activity over the western North Pacific (WNP). The principal modes of the interannual variability in the IPWP Hadley circulation were calculated using empirical orthogonal function (EOF) analysis. The leading mode (EOF-1) features cross-equatorial southerly wind anomalies over the Indian Ocean and Maritime Continent and has an evident impact on WNP TC activity during summer. In the summer following a positive phase of the EOF-1, a cyclonic circulation anomaly, with upward motion, positive relative vorticity anomalies, and weak sea level pressure, dominates the WNP, and this favors increased TC genesis. However, large positive vertical wind shear anomalies over the South China Sea and Philippine Sea inhibit the TC intensification. A positive wind–sea surface temperature (SST)–precipitation feedback was found to facilitate the ability of the signal of the EOF-1 to persist until the summer. The westerly wind anomalies converge around 10°N over the WNP, thus increasing precipitation, and this increased precipitation enhances the westerly wind anomalies via a Gill-type response. The strengthened westerly wind anomalies increase total wind speeds, which in turn cool the SST in the Bay of Bengal and the South China Sea, and warm the SST in the eastern WNP, increasing the zonal SST gradient. Consequently, this increased zonal SST gradient further enhances the westerly wind anomalies, strengthens the monsoon trough, and increases the WNP precipitation further. Therefore, the WNP precipitation anomalies are sustained into the summer.

scholarly journals Decadal Change of the Western North Pacific Summer Monsoon Break around 2002/03

2017 ◽  
Vol 31 (1) ◽  
pp. 177-193 ◽  
Author(s):  
Ke Xu ◽  
Riyu Lu
Keyword(s):  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Meridional Circulation ◽  
Warm Pool ◽  
Mariana Islands ◽  
Decadal Change ◽  
Pacific Warm Pool ◽  
Break Region ◽  
The Western Pacific

Abstract A significant decadal change is detected in the break of the western North Pacific summer monsoon (WNPSM) around 2002/03. For the period 1979–2002, the monsoon break occurs in early August, accompanied by noticeable convection suppression over the ocean to the east of the Mariana Islands (10°–20°N, 140°–160°E). However, for the period 2003–11, the monsoon break there is delayed until mid-August. This decadal change is attributable to the differences in the evolution of the WNPSM. Over this break region, convection becomes weaker after its peak in late July for the former period, and the monsoon break appears in early August. In contrast, for the latter period, convection continues strengthening in late July and reaches its peak in early August, and the monsoon break is delayed until mid-August. The differences in the evolution of sea surface temperature (SST) in the western Pacific warm pool region are responsible for the decadal change in the evolution of the WNPSM. In contrast to the former period, for the latter period the southern extent of the warm pool is remarkably warmed, and tends to be higher than the northern extent in mid- and late July, which enhances atmospheric convection nearby but inhibits the development of convection over the northern extent through a local meridional circulation. As the SST in the northern extent continues warming and becomes higher than that in the southern extent, the convection over the northern extent reaches its maximum intensification in early August. The presented results highlight that the spatial pattern of SST changes can modulate the subseasonal evolution of the WNPSM.

scholarly journals PDO-Related Wintertime Atmospheric Anomalies over the Midlatitude North Pacific: Local versus Remote SST Forcing

2020 ◽  
Vol 33 (16) ◽  
pp. 6989-7010 ◽  
Author(s):  
Lingfeng Tao ◽  
Xiu-Qun Yang ◽  
Jiabei Fang ◽  
Xuguang Sun
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Transient Eddy ◽  
Atmospheric Variability ◽  
Ridge Structure ◽  
Sst Gradient ◽  
Meridional Sst Gradient ◽  
Sst Anomalies

AbstractObserved wintertime atmospheric anomalies over the central North Pacific associated with the Pacific decadal oscillation (PDO) are characterized by a cold/trough (warm/ridge) structure, that is, an anomalous equivalent barotropic low (high) over a negative (positive) sea surface temperature (SST) anomaly. While the midlatitude atmosphere has its own strong internal variabilities, to what degree local SST anomalies can affect the midlatitude atmospheric variability remains unclear. To identify such an impact, three atmospheric general circulation model experiments each having a 63-yr-long simulation are conducted. The control run forced by observed global SST reproduces well the observed PDO-related cold/trough (warm/ridge) structure. However, the removal of the midlatitude North Pacific SST variabilities in the first sensitivity run reduces the atmospheric response by roughly one-third. In the second sensitivity run in which large-scale North Pacific SST variabilities are mostly kept, but their frontal-scale meridional gradients are sharply smoothed, simulated PDO-related cold/trough (warm/ridge) anomalies are also reduced by nearly one-third. Dynamical diagnoses exhibit that such a reduction is primarily due to the weakened transient eddy activities that are induced by weakened meridional SST gradient anomalies, in which the transient eddy vorticity forcing plays a crucial role. Therefore, it is suggested that midlatitude North Pacific SST anomalies make a considerable (approximately one-third) contribution to the observed PDO-related cold/trough (warm/ridge) anomalies in which the frontal-scale meridional SST gradient (oceanic front) is a key player, although most of those atmospheric anomalies are determined by the SST variabilities outside of the midlatitude North Pacific.

scholarly journals The Heat Balance of the Western Hemisphere Warm Pool

2005 ◽  
Vol 18 (14) ◽  
pp. 2662-2681 ◽  
Author(s):  
David B. Enfield ◽  
Sang-ki Lee
Keyword(s):  
Heat Flux ◽  
Gulf Of Mexico ◽  
Heat Balance ◽  
North Pacific ◽  
Mixed Layer Depth ◽  
Warm Pool ◽  
Western Hemisphere ◽  
Flux Divergence ◽  
Pacific Warm Pool ◽  
The Heat Balance

Abstract The thermodynamic development of the Western Hemisphere warm pool and its four geographic subregions are analyzed. The subregional warm pools of the eastern North Pacific and equatorial Atlantic are best developed in the boreal spring, while in the Gulf of Mexico and Caribbean, the highest temperatures prevail during the early and late summer, respectively. For the defining isotherms chosen (≥27.5°, ≥28.0°, ≥28.5°C) the warm pool depths are similar to the mixed-layer depth (20–40 m) but are considerably less than the Indo–Pacific warm pool depth (50–60 m). The heat balance of the WHWP subregions is examined through two successive types of analysis: first by considering a changing volume (“bubble”) bounded by constant temperature wherein advective fluxes disappear and diffusive fluxes can be estimated as a residual, and second by considering a slab layer of constant dimensions with the bubble diffusion estimates as an additional input and the advective heat flux divergence as a residual output. From this sequential procedure it is possible to disqualify as being physically inconsistent four of seven surface heat flux climatologies: the NCEP–NCAR reanalysis (NCEP1) and the ECMWF 15-yr global reanalysis (ERA-15) because they yield a nonphysical diffusion of heat into the warm pools from their cooler surroundings, and the unconstrained da Silva and Southampton datasets because their estimated diffusion rates are inconsistent with the smaller rates of the better understood Indo–Pacific warm pool when the bubble analysis is applied to both regions. The remaining surface flux datasets of da Silva and Southampton (constrained) and Oberhuber have a much narrower range of slab surface warming (+25 ± 5 W m−2) associated with bubble residual estimates of total diffusion of –5 to –20 W m−2 (±5 W m−2) and total advective heat flux divergence of –2 to –14 W m−2 (±5 W m−2). The latter are independently confirmed by direct estimates using wind stress data and drifters for the Gulf of Mexico and eastern North Pacific subregions.

scholarly journals On Relationships between Nonrecurving Western North Pacific Tropical Cyclones, the Madden–Julian Oscillation, and the East Asian Subtropical Jet

2019 ◽  
Vol 76 (3) ◽  
pp. 893-917
Author(s):  
Lawrence C. Gloeckler ◽  
Paul E. Roundy
Keyword(s):  
Tropical Cyclones ◽  
Zonal Wind ◽  
North Pacific ◽  
Western North Pacific ◽  
North Pacific Ocean ◽  
Grid Point ◽  
East Asian ◽  
Warm Pool ◽  
Madden Julian Oscillation ◽  
Subtropical Jet

Abstract A 200-hPa zonal momentum budget is performed to examine the role that western North Pacific tropical cyclones (TCs) play in helping to organize intraseasonal extratropical circulation anomalies that occur with the Madden–Julian oscillation (MJO). Zonal wind is linearly decomposed into components that occur on MJO time scales (i.e., 20–100-day periods), as well as those that occur with lower and higher frequency. Dates during Northern Hemisphere fall that feature nonrecurving TCs within a search radius centered on a South China Sea grid point when the MJO is convectively active over the Maritime Continent and west Pacific warm pool are used to generate composites of relevant budget terms. These composites are then compared to others that are based on the full list of dates that feature a convectively active MJO in the same location during NH fall without regard for TC presence. Composite results highlight the primary momentum sources that guide the evolution of the NH extratropical zonal wind and associated mass field in each event set. TCs help to accelerate the East Asian subtropical jet that evolves with the MJO by modulating the high-frequency subtropical circulation over Southeast Asia. The phasing of this circulation with its underlying MJO time-scale component enables it to transfer momentum to the emerging subtropical jet. This momentum is integrated into the more slowly evolving flow and carried forward by other processes, which leads to the development of a westerly momentum surge along the subtropical jet that spans the length of the North Pacific Ocean.

scholarly journals The Record-Breaking Hot Summer in 2015 over Hawaii and Its Physical Causes

2017 ◽  
Vol 30 (11) ◽  
pp. 4253-4266 ◽  
Author(s):  
Zhiwei Zhu ◽  
Tim Li
Keyword(s):  
North Pacific ◽  
North Atlantic Ocean ◽  
Surface Air Temperature ◽  
Warm Pool ◽  
Trade Winds ◽  
Pacific Warm Pool ◽  
Sea Surface Temperature Anomalies ◽  
Sst Warming ◽  
The Tropics ◽  
Central North Pacific

Abstract Hawaiian surface air temperature (HST) during the summer of 2015 (from July to October) was about 1.5°C higher than the climatological mean, which was the hottest since records began in 1948. In the context of record-breaking seasonal-mean high temperature, 98 exceptional local heatwave days occurred during the summer of 2015. Based on diagnoses and simulations, this paper demonstrates that the record-high HST during the summer of 2015 arose mainly from the combined effects of the interannual and interdecadal variability of sea surface temperature anomalies (SSTAs). The interannual variability of SSTAs, with an El Niño–like pattern in the tropics and cold (warm) anomalies over the western (eastern) North Pacific, was the primary contributor to the abnormally high HST in the summer of 2015. This interannual tropical–extratropical SSTA pattern was accompanied by low-level southwesterly anomalies over the central North Pacific, which weakened the climatological northeasterly trade winds and reduced the ventilation effect, warming Hawaii. Numerical experiments further revealed that the SST warming in the subtropical eastern North Pacific was mostly responsible for the weakened trade winds and warming over Hawaii. Interdecadal SST warming in the tropics was a secondary factor. By superimposing the positive SSTAs over the Indo-Pacific warm pool and tropical North Atlantic Ocean upon the climatological-mean maximum SST regions, it was found that these anomalies led to enhanced convection over the Maritime Continent and the oceans around Mexico, causing anomalous subsidence and reduced cloud cover over the tropical central North Pacific. The reduced cloudiness increased the amount of downward solar radiation, thus warming Hawaii.

Role of the western hemisphere warm pool in climate variability over the western North Pacific

2019 ◽  
Vol 53 (5-6) ◽  
pp. 2743-2755 ◽  
Author(s):  
Jae-Heung Park ◽  
Jong-Seong Kug ◽  
Soon-Il An ◽  
Tim Li
Keyword(s):  
Climate Variability ◽  
North Pacific ◽  
Western North Pacific ◽  
Warm Pool ◽  
Western Hemisphere
Sign in / Sign up

Export Citation Format

Share Document