Trends in Planetary Boundary Layer Height over Europe

Estimates of trends in planetary boundary layer height over Europe are presented, based on daily radiosonde observations at 25 stations during 1973–2010 and using a bulk Richardson number approach to determine heights. Most stations show statistically significant increases in daytime heights in all four seasons, but fewer show statistically significant trends in nighttime heights. Daytime height variations show an expected strong negative correlation with surface relative humidity and strong positive correlation with surface temperature at most stations studied, on both year-to-year and day-to-day time scales. Similar relations hold for long-term trends: increasing daytime boundary layer height is associated with decreasing surface relative humidity and increasing surface temperature atmost stations. The extent towhich these changes are regionally representative or local reflections of environmental changes near the observing stations is difficult to ascertain.