20.3. Sounding attributes

The tropopause is found where there is a distinct change from a positive lapse rate (temperature decreasing with height) in the troposphere to a negative lapse rate (temperature increasing with height) in the stratosphere. This distinction is not always clear. In general, the height of the tropopause is greater in low latitudes than it is in high latitudes. This is a result of the hypsometric equation, which states mathematically that the thickness of a layer of atmosphere is a function of the average virtual temperature of that layer.

There sometimes are layers below the tropopause where temperatures increase with height in a shallow layer; these are called a temperature “inversion” or simply “inversion”. These inversions can be caused by frontal passages, overnight cooling at the surface, or the result of sinking air (subsidence). Often accompanying the increase in temperature with height is usually a sharp decrease in dew-point temperature with height, when this happens the inversion is a result of subsidence (sinking), which is a drying process.

The vertical profile of wind speed and direction can be important in atmospheric stability assessment. Winds that are changing direction counterclockwise with height are known as backing winds, while those that are changing direction clockwise with height are known as veering winds. Backing winds are associated with cold air advection, which tends to promote sinking motion. While, veering winds are associated with warm air advection, which tends to promote rising motion.

Mandatory and Significant Levels

The data collected by the radiosonde is encoded for mandatory and significant levels only, even though the instruments are continuously measuring data during the radiosonde flight.

The mandatory levels are: 1000, 925, 850, 700, 500, 400, 300, 250, 200, 150, 100, 70, 50, and 10 (all in mb)

These do not change. Data are always reported from these pressure levels.

Significant levels are altitudes where sensors detect a rapid change in the vertical profile of temperature, moisture, and/or wind speed or direction. The additional handout today is a sampling of decoded data from our recent balloon launch