Synoptic-scale variability of the polar and subpolar tropopause: Data analysis and idealized PV inversions

Abstract

The synoptic-scale variability of the polar and subpolar tropopause is investigated based on radiosonde and European Centre for Medium-Range Weather Forecasts Reanalysis data in combination with idealized potential vorticity (PV) inversions. A regression analysis is performed to examine the relationship between the relative vorticity at tropopause level, the tropopause displacement, the static stability above the tropopause, and the anomalies of tropopause temperature and potential temperature. The results are compared with regression coefficients computed from a large number of PV inversions. Generally, a cyclonically influenced tropopause is lower, warmer and potentially colder than average, and the static stability above the tropopause is reduced. The opposite is true under anticyclonic influence. Typically, a cyclonic vorticity of 10−5s−1 is associated with a decrease of the tropopause height by 150–200 m. Correspondingly, the mean vertical temperature gradient in the lowermost 2 km above the tropopause decreases by 0.2– 0.3 K km−1. Moreover, an increase of the tropopause height by 1 km is associated with a temperature decrease by 3–5 K and an increase of the potential temperature by 6–8 K. Except for the last one, these values do not depend significantly on the strength and the sign of the tropopause anomaly. Distinct annual cycles are observed in parts of the polar regions. Most of the relations found in the data can be reproduced with the PV inversions, except for the observed linearity for large tropopause displacements which is not always reproduced very well. The annual cycles can be partly explained with the aid of the PV inversions. Copyright © 2002 Royal Meteorological Society