Trends in temperature and wind speed from 40 years of observations at a 200‐m high meteorological tower in Southwest Germany

Abstract

ABSTRACT Forty years of temperature and wind measurements at Karlsruhe Institute of Technology's 200‐m high meteorological tower in the Upper Rhine Valley in Southwest Germany are used to calculate trends in the mixed and residual layer respectively, which can be compared to trends in the surface layer. For trend analysis, the Mann–Kendall test is used. Data are analysed on an annual, seasonal, and daily scale. For the variable temperature, a significant positive annual trend is found. Seasonally, the strongest temperature increases are observed in spring and summer. This is also reflected by significant positive trends for meteorological indices such as summer days, tropical days, and growing season length. On a daily scale, the strongest temperature increase is found in the mixed layer during nighttime. This results in a stronger stable stratification and in a higher number of surface inversions. Wind speed measurements reveal a significant negative annual trend in the mixed layer at a height of 200 m. Seasonally, weakly negative trends are found for spring and summer. It can be shown that the trends for wind speed are only partly be related to modifications of surface roughness in the vicinity of the site.