On the occurrence of strong vertical wind shear in the tropopause region: a 10-year ERA5 northern hemispheric study

Publikationstyp:
Zeitschriftenaufsatz
Metadaten:
Autoren
  • Thorsten Kaluza
  • Daniel Kunkel
  • Peter Hoor
Autoren-URL
https://www.webofscience.com/api/gateway?GWVersion=2&SrcApp=fis-test-1&SrcAuth=WosAPI&KeyUT=WOS:001166583500001&DestLinkType=FullRecord&DestApp=WOS_CPL
DOI
10.5194/wcd-2-631-2021
eISSN
2698-4016
Externe Identifier
  • Clarivate Analytics Document Solution ID: IL8W5
Ausgabe der Veröffentlichung
3
Zeitschrift
WEATHER AND CLIMATE DYNAMICS
Paginierung
631 - 651
Datum der Veröffentlichung
2021
Status
Published
Titel
On the occurrence of strong vertical wind shear in the tropopause region: a 10-year ERA5 northern hemispheric study
Sub types
  • Article
Ausgabe der Zeitschrift
2

Datenquelle: Web of Science (Lite)

Andere Metadatenquellen:
Abstract
<jats:p>Abstract. A climatology of the occurrence of strong wind shear in the upper troposphere–lower stratosphere (UTLS) is presented, which gives rise to defining a tropopause shear layer (TSL). Strong wind shear in the tropopause region is of interest because it can generate turbulence, which can lead to cross-tropopause mixing. The analysis is based on 10 years of daily northern hemispheric ECMWF ERA5 reanalysis data. The vertical extent of the region analyzed is limited to the altitudes from 1.5 km above the surface up to 25 km, to exclude the planetary boundary layer as well as strong wind shear in higher atmospheric layers like the mesosphere–lower thermosphere. A threshold value of St2=4×10-4s-2 of the squared vertical shear of the horizontal wind is applied, which marks the top end of the distribution of atmospheric wind shear to focus on situations which cannot be sustained by the mean static stability in the troposphere according to linear theory. This subset of the vertical wind shear spectrum is analyzed for its vertical, geographical, and seasonal occurrence frequency distribution. A set of metrics is defined to narrow down the relation to planetary circulation features, as well as indicators for momentum-gradient-sharpening mechanisms. The vertical distribution reveals that strong vertical wind shear above the threshold occurs almost exclusively at tropopause altitudes, within a vertically confined layer of about 1–2 km in extent directly above the local lapse rate tropopause. The TSL emerges as a distinct feature in the tropopause-based 10-year temporal and zonal mean climatology, spanning from the tropics to latitudes around 70∘ N, with average occurrence frequencies on the order of 1 %–10 %. The horizontal distribution of the strong vertical wind shear near the tropopause exhibits distinctly separated regions of occurrence, which are generally associated with jet streams and their seasonality. At midlatitudes, strong wind shear values occur most frequently in regions with an elevated tropopause and at latitudes around 50∘ N, associated with jet streaks within northward-reaching ridges of baroclinic waves. At lower latitudes in the region of the subtropical jet stream, which is mainly apparent over the east Asian continent, the occurrence frequency of strong wind shear near the tropopause reaches maximum values of about 30 % during winter and is tightly linked to the jet stream seasonality. The interannual variability of the occurrence frequency for strong wind shear might furthermore be linked to the variability of the zonal location and strength of the jet. The east-equatorial region features a bi-annual seasonality in the occurrence frequencies of strong vertical wind shear near the tropopause. During the summer months, large areas of the tropopause region over the Indian Ocean are up to 70 % of the time exposed to strong wind shear, which can be attributed to the emergence of the tropical easterly jet. During winter, this occurrence frequency maximum shifts eastward over the maritime continent, where it is exceptionally pronounced during the DJF 2010/11 La Niña phase, as well as quite weak during the El Niño phases of 2009/10, 2014/15, and 2015/16. This agrees with the atmospheric response of the Pacific Walker circulation cell in the El Niño–Southern Oscillation (ENSO) ocean–atmosphere coupling. </jats:p>
Autoren
  • Thorsten Kaluza
  • Daniel Kunkel
  • Peter Hoor
DOI
10.5194/wcd-2-631-2021
eISSN
2698-4016
Ausgabe der Veröffentlichung
3
Zeitschrift
Weather and Climate Dynamics
Sprache
en
Online publication date
2021
Paginierung
631 - 651
Status
Published online
Herausgeber
Copernicus GmbH
Herausgeber URL
http://dx.doi.org/10.5194/wcd-2-631-2021
Datum der Datenerfassung
2021
Titel
On the occurrence of strong vertical wind shear in the tropopause region: a 10-year ERA5 northern hemispheric study
Ausgabe der Zeitschrift
2

Datenquelle: Crossref

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