Research Institute for Sustainable Humanosphere

A study on the variation of the tropical tropopause by using high precision satellite data
精密衛星観測データを用いた熱帯の対流圏界面の変動特性に関する研究

氏名 Sanjay Kumar MEHTA
共同研究者 津田敏隆
採択年 2011(平成23) 年度

One of the important goals of the Mission 1 is to deepen understanding of the current condition and fluctuations of the Humanosphere by developing research involving observation of the atmosphere. In a climatic perspective temperature changes in troposphere and stratosphere will be an important asset to examine.

It is well known that the tropospheric temperature is warmer due to presence of the natural greenhouse gases than it would have attained by radiative equilibrium in absence of the fluid motion. However, if fluid motion is considered the temperature is finally determined by the convective-radiative equilibrium of the atmosphere. Recently, it is observed that both natural greenhouse gases (GHGs) and anthropogenic GHGs (e.g. chlorofluorocarbons (CFCs)) shows increasing trends which caused increase the tropospheric temperatures. A number of studies have confirmed that warming trends of the troposphere (due to increase of CO2) and cooling trends of the stratosphere (due to depletion of O3) since a past few decades. The increasing rate of tropospheric temperature trends is 0.1–0.2 K/decade while decreasing rate of the stratospheric temperature trends is ~−0.5 K/decade. The temperatures trends in the troposphere and stratosphere are not uniform everywhere and show altitude, latitudinal and seasonal structures.

Tropopause separates the turbulently mixed troposphere and stably stratified stratosphere. It has been observed that the tropopause temperature shows cooling trends and tropopause altitude shows increasing trends. The altitude profile of the temperature trends transits from tropospheric warming to stratospheric cooling at some level ~250–150 hPa. This transition occurs just below the tropopause. Thus the upper troposphere between tropopause and transition layer also show cooling trend. The physical signification of the transition layer is expected to be related as the region where the effect of the both of GHGs on the troposphere and O3 depletion in the stratosphere is minimizes.

There are a few uncertainties regarding the use of the definition in the determination of the global tropopause. For the trend analysis of the global tropopause the lapse rate tropopause (WMO definition) has been used as a robust definition simply because it can be applied for whole globe. However, the limitation of lapse rate tropopause is known. Using high precision satellite such as GPS RO satellite, the following objectives will be carried out as a mission research fellow.

  1. The effect of the short scale variability due to synoptic scale disturbances, equatorial wave activity, planetary wave activity and sudden stratospheric warming planetary wave in the trend analysis.
  2. Examination of the transition region between the tropospheric warming and stratospheric cooling and its relationship with tropopause.
  3. The GPS RO provides precise bending angle profile which can be used to determine the climatic tropopause trend which will have less uncertainty than temperature.
  4. The impact of the tropospheric warming and stratospheric cooling in the stratosphere-troposphere exchange process.

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