ABSTRACT
The focus of this chapter is on the issues of monitoring water vapor in troposphere and stratosphere. The water vapor distribution in the upper troposphere (UT) and lower stratosphere (LS) is of central importance in several ways: it plays a major role in the balance of planetary radiation; it influences and responds to atmospheric motions; and it plays a key role in many aspects of UT/LS chemistry. Effects on the radiation balance are especially important because the water vapor molecule is strongly polar in shape giving it a strongly absorbing infrared spectrum. It was found that the increased stratospheric water vapor levels could also enhance ozone destruction. This means that the increase in the stratospheric concentration of water vapor presents a continuing threat to the global ozone layer.
The previous chapters have shown that atmospheric water vapor is abundant in the atmosphere and possesses absorption features spread over a broad range of the electromagnetic spectrum. Therefore, one can assume that it should be easy to measure the concentration of water vapor in upper troposphere and stratosphere using balloons and aircrafts. However, analysis carried out in the present chapter shows that water vapor measurements in these areas have proved to be difficult. Water sticks to surfaces, thereby providing challenges for in situ techniques. Sharp vertical and horizontal gradients present difficulties for remote-sensing techniques. In addition, a lack of understanding of the fundamental physics behind the observed spectrum complicates the analysis of remote-sensing measurements. Peculiarities of aircraft observations, factors influencing the in-flight performance, and comparative characteristics of the devices used for the upper tropospheric and stratospheric measurements are also discussed in the present chapter.
