Stratospheric water vapour and tropical tropopause temperatures in Ecmwf analyses and multi‐year simulations

作者：Adrian John Simmons, Agathe Untch, Christian Jakob, Per W. Kållberg, Per Undén · 发表于：Quarterly Journal of the Royal Meteorological Society · 年份：1999 · DOI：10.1002/qj.49712555318 · 被引用次数：162 · 研究领域：Atmospheric Ozone and Climate、Climate variability and models、Atmospheric chemistry and aerosols

Abstract Stratospheric humidity analyses produced operationally by the European Centre for Medium‐Range Weather Forecasts (ECMWF) are discussed for the period since late January 1996 when the practice of resetting the upperlevel specific humidity to a fixed value at each analysis time was abandoned. Near‐tropopause analyses are in reasonable overall agreement with independent observations. Very low humidities occur in conjunction with deep convection and a particularly cold tropopause over the equatorial western Pacific during the northern winter. Drying occurs also in the cold core of the Antarctic polar‐night vortex. the lower stratosphere is moistened in the outer tropics and subtropics in summer and autumn, predominantly in the northern hemisphere. Changes associated with the latest occurrence of El Niño are illustrated. Analysed temperatures near the tropical tropopause are generally in good agreement with corresponding radiosonde measurements, with standard‐level biases of the order of 0.5 degC or less. the past two years are the coldest by about 1 degC in a series of tropical mean 100 hPa analyses extending back to 1979. A cooling trend of about 0.6 degC per decade is seen in the global means of the 100 hPa analyses. Moisture is spread zonally and upward from the tropical tropopause as the data assimilation proceeds, but the rate of upward transfer is much faster than observed. Substantial lateral mixing can occur within the stratosphere over the course of a season. Mo...