Universität zu Köln

Steinheuer, Julian ORCID: 0000-0001-9835-4277 (2023). Vertical wind gust profiles. PhD thesis, Universität zu Köln.

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Abstract

Wind gusts are usually available for a height of 10 m above ground level, either through the standard wind measurement network or also as a diagnostic variable in numerical weather prediction (NWP). They are relevant for many applications and represent the variable that best characterizes severe wind situations, since they quantify the strongest winds. Mostly, high wind gust peaks recorded at 10 m are related to stronger winds at the heights above, and also, their origin is usually located here. However, high-resolution profiling of the wind is lacking, so only a limited amount of observations exist to study the processes that transport wind gusts or reveal much about their vertical structure. Wind profiles can be recorded at meteorological towers, but these are only found at very few sites because they are costly to operate and then they can only cover the lower few hundred meters of the atmosphere. A wind gust is a short-lived wind spike and represents a phenomenon too small-scale to be resolvable in common weather models. Hence, the gusts are parameterized and derived from other diagnostic variables. However, this is usually done only for the wind gust peak in 10 m. Therefore, there is a lack of wind gust profiling opportunities in both the NWP and the observations. The present thesis addresses both weather models and new observational methods to generate wind gust profiles. A statistical post-processing is developed that is able to generate a distribution function of gust profiles in the entire lower 250 m of the atmosphere using other atmospheric variables. The post-processing is based on measurements from the weather mast in Hamburg for an observation period of 11 years and uses variables of the regional reanalysis COSMO-REA6 as predictors for a generalized extreme value distribution specifying the occurrence probabilities of hourly gust peaks. This post-processing is not only able to improve the existing gust diagnostics in 10 m of the reanalysis, but also to provide a suitable prediction for heights up to 250 m including intermediate heights without gathered observations. The second part of the thesis explores the possibilities to obtain wind gust profiles with a Doppler wind lidar (DWL). A comparative study provides a DWL configuration - the quick continuous scanning mode - which allows to acquire about 11 measurements of the Doppler velocity in about 3.4 s, allowing to generate wind vector profiles with high temporal resolution. For this purpose a retrieval is developed, that can provide wind gust peaks, which agree excellently with the standard gust measurements of a sonic anemometer. Furthermore, the high-resolution time-series can reflect the variability in wind profiles in such a detail that individual case studies of high-impact weather events can be illuminated. In the field experiment on sub-mesoscale spatio-temporal variability in Lindenberg (FESSTVaL), the DWL using this new measurement configuration combined with the developed retrieval has demonstrated that it can profile the wind gusts associated with cold fronts and cold pools at such a high-resolution up to about 1500 m. Therefore, DWLs can contribute in future significantly to understanding of the underlying processes, as small-scale variabilities and wind transports can be made observable.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Steinheuer, Julian Julian.Steinheuer@gmx.de orcid.org/0000-0001-9835-4277 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-656558
Date:	2023
Place of Publication:	Köln
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology
Subjects:	Earth sciences
Uncontrolled Keywords:	Keywords Language Wind gusts; Doppler wind lidar; wind retrieval; wind profiling; extreme value theory; post-processing; regional reanalysis; FESSTVaL; cold pool; cold front; UNSPECIFIED
Date of oral exam:	13 April 2023
Referee:	Name Academic Title Löhnert, Ulrich Prof. Dr. Crewell, Susanne Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/65655