Dahlke, Sandro (2015) Global teleconnections associated with diabatic heating due to local rainfall events. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 71 pp.

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Abstract

In this thesis, atmospheric teleconnection patterns and their interannual connection to anomalous local rainfall in the summer and winter season are investigated in the period after 1979. Given the lack of quality of gridded reanalysis rainfall products, especially in the period prior to 1979, an ensemble mean estimate of three satellite-based rainfall products covering 32 years is used as a proxy for diabatic heating in the troposphere. It is shown that the diabatic heating due to local rainfall can affect the tropospheric circulation in regions very distant from the heating, while the induced teleconnections may as well affect global weather and climate. It is argued that planetary waves are responsible for communicating the teleconnections throughout the globe. Hence, anomalous Rossby Wave Sources (RWSs), that are related to the diabatic heating, are shown to drive the teleconnection patterns via generation of vorticity. It is found that the midlatitude jets play an important role for the generation of teleconnections, as they act as waveguides for planetary waves. The satellite ensemble mean rainfall in the tropical Pacific has good skill in reproducing eleconnections that are associated with El Niño, namely the projection onto the Pacific North American (PNA) pattern and the Pacific South American (PSA) pattern. It is shown that even when the signal of El Niño and the local SST is removed from the seasonal rainfall everywhere on the globe, there are regions evident, where anomalous rainfall can disturb the troposphere and generate global-scale teleconnections. Thus, anomalous diabatic heating over the central Pacific Ocean generates a westward shifted PNA pattern. Further, enhanced winter rainfall over the tropical Indian Ocean projects onto the positive phase of the North Atlantic Oscillation (NAO), which is the dominant mode of atmospheric
variability over the Atlantic sector. This finding implies a remote impact of the convective activity over the Indian Ocean on European Climate. Interannual variability of diabatic heating during the Indian Summer Monsoon (ISM) drives a circumglobal teleconnection pattern in the northern hemisphere. This pattern in turn affects climate and rainfall in several regions of the world, especially in northeast China and northern Africa. The results further suggest that teleconnection patterns associated with anomalous rainfall over the Tropical Indian Ocean, the Maritime Continent, the Indian peninsula and the Gulf Stream, bear similarities to the circumpolar wavetrain discussed in Branstator (2002). In the tropics, the atmospheric response to diabatic heating resembles the Gill-type response, emphasizing that the satellite ensemble mean rainfall is a good representation of diabatic heating in the last 32 years.

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