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.

Different Impacts of the East Asian Winter Monsoon on the Surface Air Temperature in North America during ENSO and Neutral ENSO Years

2020 ◽  
Vol 33 (24) ◽  
pp. 10671-10690
Author(s):  
Tianjiao Ma ◽  
Wen Chen ◽  
Hans-F. Graf ◽  
Shuoyi Ding ◽  
Peiqiang Xu ◽  
...  
Keyword(s):  
Wave Packet ◽  
North Pacific ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Surface Air Temperature ◽  
Winter Monsoon ◽  
Asian Winter Monsoon ◽  
The North ◽  
The North Pacific ◽  
Central North Pacific

AbstractThe present study investigates different impacts of the East Asian winter monsoon (EAWM) on surface air temperature (Ts) in North America (NA) during ENSO and neutral ENSO episodes. In neutral ENSO years, the EAWM shows a direct impact on the Ts anomalies in NA on an interannual time scale. Two Rossby wave packets appear over the Eurasian–western Pacific (upstream) and North Pacific–NA (downstream) regions associated with a strong EAWM. Further analysis suggests that the downstream wave packet is caused by reflection of the upstream wave packet over the subtropical western Pacific and amplified over the North Pacific. Also, the East Asian subtropical westerly jet stream (EAJS) is intensified in the central and downstream region over the central North Pacific. Hence, increased barotropic kinetic energy conversion and the interaction between transient eddies and the EAJS tend to maintain the circulation anomaly over the North Pacific. Therefore, a strong EAWM tends to result in warm Ts anomalies in northwestern NA via the downstream wave packet emanating from the central North Pacific toward NA. A weak EAWM tends to induce cold Ts anomalies in western-central NA with a smaller magnitude. However, in ENSO years, an anomalous EAJS is mainly confined over East Asia and does not extend into the central North Pacific. The results confirm that the EAWM has an indirect impact on the Ts anomalies in NA via a modulation of the tropical convection anomalies associated with ENSO. Our results indicate that, for seasonal prediction of Ts anomalies in NA, the influence of the EAWM should be taken into account. It produces different responses in neutral ENSO and in ENSO years.

scholarly journals High-Resolution Climate Simulations Using GFDL HiRAM with a Stretched Global Grid

2016 ◽  
Vol 29 (11) ◽  
pp. 4293-4314 ◽  
Author(s):  
Lucas M. Harris ◽  
Shian-Jiann Lin ◽  
ChiaYing Tu
Keyword(s):  
High Resolution ◽  
Warm Season ◽  
Warm Pool ◽  
Climate Simulation ◽  
Enhanced Resolution ◽  
Pacific Warm Pool ◽  
Climate Simulations ◽  
Mean Climate ◽  
The Tropics ◽  
The Western Pacific

Abstract An analytic Schmidt transformation is used to create locally refined global model grids capable of efficient climate simulation with gridcell widths as small as 10 km in the GFDL High-Resolution Atmosphere Model (HiRAM). This method of grid stretching produces a grid that varies very gradually into the region of enhanced resolution without changing the topology of the model grid and does not require radical changes to the solver. AMIP integrations were carried out with two grids stretched to 10-km minimum gridcell width: one centered over East Asia and the western Pacific warm pool, and the other over the continental United States. Robust improvements to orographic precipitation, the diurnal cycle of warm-season continental precipitation, and tropical cyclone maximum intensity were found in the region of enhanced resolution, compared to 25-km uniform-resolution HiRAM. The variations in grid size were not found to create apparent grid artifacts, and in some measures the global-mean climate improved in the stretched-grid simulations. In the enhanced-resolution regions, the number of tropical cyclones was reduced, but the fraction of storms reaching hurricane intensity increased, compared to a uniform-resolution simulation. This behavior was also found in a stretched-grid perpetual-September aquaplanet simulation with 12-km resolution over a part of the tropics. Furthermore, the stretched-grid aquaplanet simulation was also largely free of grid artifacts except for an artificial Walker-type circulation, and simulated an ITCZ in its unrefined region more resembling that of higher-resolution aquaplanet simulations, implying that the unrefined region may also be improved in stretched-grid simulations. The improvements due to stretching are attributable to improved resolution as these stretched-grid simulations were sparingly tuned.

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.

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

Winter-to-Winter Recurrence of Sea Surface Temperature Anomalies in the Northern Hemisphere

2010 ◽  
Vol 23 (14) ◽  
pp. 3835-3854 ◽  
Author(s):  
Xia Zhao ◽  
Jianping Li
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
North Pacific ◽  
Sea Surface ◽  
The North ◽  
Sea Surface Temperature Anomalies ◽  
Circulation Anomalies ◽  
Atmospheric Circulation Anomalies ◽  
The North Pacific ◽  
Central North Pacific

Abstract The spatiotemporal characteristics of the winter-to-winter recurrence (WWR) of sea surface temperature anomalies (SSTA) in the Northern Hemisphere (NH) are comprehensively studied through lag correlation analysis. On this basis the relationships between the SSTA WWR and the WWR of the atmospheric circulation anomalies, El Niño–Southern Oscillation (ENSO), and SSTA interdecadal variability are also investigated. Results show that the SSTA WWR occurs over most parts of the North Pacific and Atlantic Oceans, but the spatiotemporal distributions of the SSTA WWR are distinctly different in these two oceans. Analyses indicate that the spatiotemporal distribution of the SSTA WWR in the North Atlantic Ocean is consistent with the spatial distribution of the seasonal cycle of its mixed layer depth (MLD), whereas that in the North Pacific Ocean, particularly the recurrence timing, cannot be fully explained by the change in the MLD between winter and summer in some regions. In addition, the atmospheric circulation anomalies also exhibit the WWR at the mid–high latitude of the NH, which is mainly located in eastern Asia, the central North Pacific, and the North Atlantic. The sea level pressure anomalies (SLPA) in the central North Pacific are essential for the occurrence of the SSTA WWR in this region. Moreover, the strongest positive correlation occurs when the SLPA lead SSTA in the central North Pacific by 1 month, which suggests that the atmospheric forcing on the ocean may play a dominant role in this region. Therefore, the “reemergence mechanism” is not the only process influencing the SSTA WWR, and the WWR of the atmospheric circulation anomalies may be one of the causes of the SSTA WWR in the central North Pacific. Finally, the occurrence of the SSTA WWR in the NH is closely related to SSTA interdecadal variability in the NH, but it is linearly independent of ENSO.

The tropical atmospheric conveyor belt: a Lagrangian perspective of the large-scale tropical circulation

2020 ◽  
Author(s):  
Dana Raiter ◽  
Eli Galanti ◽  
Yohai Kaspi
Keyword(s):  
Large Scale ◽  
Meridional Circulation ◽  
Hadley Circulation ◽  
Warm Pool ◽  
Conveyor Belt ◽  
Jet Stream ◽  
Tropical Circulation ◽  
Pacific Warm Pool ◽  
Actual Movement ◽  
The Tropics

<div> <div>The Hadley circulation (HC) is a key element of the climate system. It is traditionally defined as the zonally averaged meridional circulation in the tropics, therefore treated as a zonally symmetric phenomenon. However, differences in temperature between land and sea cause zonal asymmetries on Earth, dramatically affecting the circulation. The longitudinal dependence of the HC evokes questions about where and when the actual large scale tropical circulation occurs. In this study, we look into the connection between the longitudinally dependent HC and the actual large scale movement of air in the tropics using a coupled Eulerian and Lagrangian approach. Decomposing the velocity field, we identify the components affecting the actual circulation. In addition, we calculate trajectories of air parcels to analyze the actual movement. We propose an alternative definition for the circulation, that describes the actual path of air parcels in the tropics, as a tropical conveyor belt. The Indo-Pacific warm pool is the driver of the circulation, where air converges and ascends, then moves westward and poleward before entering the jet stream, moving eastward with it, eventually beginning its descent near the Americas. Furthermore, using an idealized moist GCM, we explore how tropical asymmetries affect the circulation and discuss the possible mechanisms controlling the tropical conveyor belt.</div> </div>

scholarly journals Glacial changes in tropical climate amplified by the Indian Ocean

2018 ◽  
Vol 4 (12) ◽  
pp. eaat9658 ◽  
Author(s):  
Pedro N. DiNezio ◽  
Jessica E. Tierney ◽  
Bette L. Otto-Bliesner ◽  
Axel Timmermann ◽  
Tripti Bhattacharya ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Climate Changes ◽  
Equatorial Indian Ocean ◽  
Walker Circulation ◽  
Warm Pool ◽  
Pacific Warm Pool ◽  
The Indian Ocean ◽  
The Tropics ◽  
The Last Glacial Maximum ◽  
The Last Glacial

The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool are poorly understood. Here, we address this question by combining paleoclimate proxies with model simulations of the Last Glacial Maximum climate. We find evidence of two mechanisms explaining key patterns of ocean cooling and rainfall change interpreted from proxy data. Exposure of the Sahul shelf excites a positive ocean-atmosphere feedback involving a stronger surface temperature gradient along the equatorial Indian Ocean and a weaker Walker circulation—a response explaining the drier/wetter dipole across the basin. Northern Hemisphere cooling by ice sheet albedo drives a monsoonal retreat across Africa and the Arabian Peninsula—a response that triggers a weakening of the Indian monsoon via cooling of the Arabian Sea and associated reductions in moisture supply. These results demonstrate the importance of air-sea interactions in the Indian Ocean, amplifying externally forced climate changes over a large part of the tropics.

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