Authors:	Fragkoulidis, Georgios
Title:	Rossby Wave Packets and their Role in Temperature Extremes
Online publication date:	31-Oct-2019
Year of first publication:	2019
Language:	english
Abstract:	Eastward propagating Rossby wave packets (RWPs) are a dominant feature of the mid-latitude circulation. They are reflected in the upper-tropospheric meridional wind field as a longitudinally-confined group of northerlies and southerlies. Their documented relevance to weather extremes necessitates the development of diagnostic methods that can identify and investigate their properties locally in space and time. The overarching goal of this work is to develop such diagnostics, investigate the local properties of RWPs and quantify their role in temperature extremes. The diagnostic methods are based on the analytic signals of the filtered upper-tropospheric meridional wind and its envelope function along latitude circles. RWP properties like the local amplitude, wavelength, phase velocity, and group velocity collectively provide the main characteristics of the upper-tropospheric flow in the mid-latitudes at any instance in time, but also reveal its distinct climatological patterns. Based on them, the role of RWPs in the occurrence and duration of temperature extremes is investigated. In particular, regression analyses show that the probability for a temperature extreme in many parts of the Northern Hemisphere increases significantly with RWP amplitude; a linkage that cannot be revealed so clearly when employing non-local metrics like the Fourier amplitudes of meridional wind. The role of RWPs as large-scale upstream precursors is further emphasized in an investigation of Southeastern European hot and cold extremes. Identifying and following the spatiotemporal evolution of RWPs also proves beneficial in exploring the lifetime of the 2003 and 2010 heat waves in Western Europe and Russia respectively. In doing so, it is shown that a single one or several successive non-circumglobal RWPs can create the large-scale environment where temperature anomalies can amplify and --- in combination with physical processes of smaller scale --- lead to extreme events. During such cases of persistent temperature extremes the role of below-normal RWP phase velocity is found to be critical. The combined effect of RWP amplitude and phase velocity in the occurrence and duration of temperature extremes is quantified using a sufficiently large sample of short-lived and persistent events in 40 years of reanalysis data (1979--2018). Global climatologies of local RWP amplitude, phase velocity and group velocity are produced for the first time and reveal the major differences in the upper-tropospheric circulation of the Northern and Southern Hemispheres. Moreover, important aspects of the seasonal variability in particular regions are discussed. Finally, an investigation of medium-range forecast biases of the Northern Hemisphere RWP properties using 6 years of ECMWF operational forecasts (2013--2018) suggests possible implications for the practical predictability of temperature extremes occurrence and duration. Overall, this work contributes to the overarching goal of improving our understanding of RWPs and temperature extremes. The aforementioned findings and the novel diagnostics will be beneficial for future research on the processes that affect the RWP evolution and its implications to the occurrence and predictability of extremes at both the weather and climate time scales.
DDC:	500 Naturwissenschaften 500 Natural sciences and mathematics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 08 Physik, Mathematik u. Informatik
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-2357
URN:	urn:nbn:de:hebis:77-diss-1000031418
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Extent:	iv, 123 Seiten
Appears in collections:	JGU-Publikationen