2. Investigate the vertical moisture distribution

The next step consists of identifying the location of the moisture in the vertical profile.

The moisture in ARs is characterized by:

  • high water vapour concentrations at layers below 700 hPa.

This characteristic of ARs is best analysed from model humidity fields.

Figure 6: Vertical cross section through an AR. A bulge of high relative humidity values reaching up to 700 hPa
can be seen in the middle of the cross section.


Figure 7: Left: 2-D charts of relative humidity at levels 500, 700 and 850 hPa. Right: Schematic of the relative humidity charts.


Most of all, "rivers in the sky" are characterized by their flow. In the next chapter, we find out how these moisture bands behave like rivers.


Exercise 2

Click on the images and go through the gallery, then answer the question.

Identify the model cross sections that show signs of an AR.



There is a clear maximum in relative humidity below 700 hPa in the middle of the cross section. This looks like an AR. With high humidity values reaching up to 300 hPa, this could be an AR in the vicinity of a cold front.


The moisture maximum is located in lower levels, however, the air below the maximum is dry. This is very uncommon for an AR.


This is the typical moisture distribution for ARs when they start to develop.


There is no humidity maximum at lower levels, hence there is no AR.