dc.contributor.advisor Wang, Bin Xie, Zhiling
dc.contributor.department Atmospheric Sciences 2022-03-03T19:53:34Z 2022-03-03T19:53:34Z 2021 Ph.D.
dc.subject Atmospheric sciences
dc.subject Climate change
dc.subject Future changes
dc.subject Heat sources
dc.subject Interannual variations
dc.subject Tibetan Plateau
dc.type Thesis
dcterms.abstract The spatial-temporal characteristics of the summer atmospheric heat sources over the Tibetan Plateau (TP) are revisited in the first part of this dissertation, applying various bias-corrected datasets, including reanalyses, gauge observations, and satellite products. Verification-based selection and ensemble-mean methods are taken to combine multiple datasets. Compared to previous studies focused on the eastern TP, this study pays special attention to the heat sources over the data-void western plateau. A climatological minimum in the total heat is found in the high-altitude region of the northwestern TP. The TP total heat showed insignificant trends over the eastern and central TP (ETP/CTP) during 1984–2006, whereas exhibited an evident increasing trend over the western TP (WTP). The interannual variation of total heat over the central-eastern TP is dominated by the variation of latent heat from precipitation. However, over the western TP, the variation of the total heat is highly correlated with net radiation and surface sensible heat. The remote forcings and impacts of the interannual variations in summer heat sources over the eastern, central, and western TP are investigated in the second and third parts with observational analyses and numerical model experiments. The summer heat source variability is affected by different remote forcings across the TP from east to west. The ETP precipitation (i.e., latent heating) is likely modulated by North Atlantic Oscillation (NAO) and associated SST anomalies through large-scale wave trains propagating from Western Europe to East Asia. On the other hand, the increased CTP precipitation is primarily driven by a developing La Niña through generating southerly wind anomalies to the south of the CTP, enhancing moisture transport and precipitation over the southern CTP. The increased WTP sensible heating is linked to the tropical western Pacific cooling, central Pacific warming, and North Atlantic cooling. These anomalous SST conditions produce a high-pressure anomaly over the WTP, raising the ground-air temperature difference, thereby enhancing the WTP sensible heat. The results in the third part show that the ETP, CTP, and WTP heat sources have different impacts on regional climate and teleconnection. A warming center in northwestern Asia and a cooling center in western Europe are connected with the ETP heating. The CTP heating is related to northeastern Asian warming and East Asia cooling. The WTP heating is linked to the warming in southeastern China and the polar region of Asia. The linear wave-train responses to the TP heating forcings exhibit notable differences. The ETP heating generates an upper-level wave train propagating eastward to the northwestern Pacific. The wave train excited by the CTP heating propagated far eastward to central North Pacific. The WTP heating produces a wave train that splits into two branches, the northern one propagating northeastward to the Arctic region and the southern one propagating eastward to coastal northwestern Pacific. The fourth part of this dissertation presents 22 CMIP6 models’ performances and future projections for the eastern-TP summer precipitation and sensible heat flux. Nearly all models can well simulate the observed climatological precipitation pattern (1979–2014) but overestimate the mean by 65%. For sensible heat, nearly half of the models can hardly capture the spatial structure. The multimodel ensemble mean of selected high-performance models projects that, under the medium emission scenario (SSP2-4.5), the summer precipitation will likely increase by 2.7% per degree Celsius global warming due to the future enhancement in surface evaporation and vertical moisture transport that are partially offset by weakening ascending motion. The projected sensible heat will likely remain unchanged, associated with the likely unaltered surface wind speed.
dcterms.extent 126 pages
dcterms.language en
dcterms.publisher University of Hawai'i at Manoa
dcterms.rights All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
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