Skew-T log-P diagram

A vertical profile, or Temp is a graph showing the air temperature, the dew point, wind speed and the wind direction in dependence of the height. The necessary data are obtained from radiosondes, which rise from weather stations at regular intervals into the atmosphere.

Since the air pressure above the barometric formula is related exponentially with height, the height scale is often replaced by a logarithmic pressure scale.

Representation

There are various different display modes, for example, Stuve - diagram or the skew - T diagram. Various auxiliary lines to facilitate the orientation in the chart on this day. (see adjacent figure):

• Isobars are lines of constant Drucks. They run parallel to the T axis and each represent a certain level. In the figure, the pressure in mbar ( hPa = ) and the height was specified in feet.
• Isotherms are lines of constant temperature. In the Stuve diagram they run parallel to the log- p- axis, in the skew - T diagram they are against this inclined (hence the name Skew -T from English "skew " = wrong ).
• Trockenadiabaten are lines of constant energy. A parcel of air rises into the atmosphere, cools and expands to conform to the ambient pressure. If this produces no energy is exchanged with the environment, it is called an adiabatic ascent. The diagram shows the Trockenadiabaten are the ausgezogenenen, curved lines.
• Feuchtadiabaten: moist air rises, so moisture condenses and thereby releasing heat of condensation. This heat will go to the air parcel, which is why the temperature drops less when feuchtadiabatischen ascent. The Feuchtadiabaten thus extend steeper than the Trockenadiabaten. Here they are shown with broken lines.
• Saturation curves: These lines indicate the temperature of a saturated air-water vapor mixture in a given composition, depending on the pressure ( and thus of the height) of. In this representation, they are drawn with dashed lines and run approximately parallel to the isotherms.

Interpretation

The interpretation of the vertical profile is illustrated by the example shown.

The following questions can be answered with the vertical profile:

Humidity

The dew point is a measure of the absolute humidity. If you want the absolute humidity at a certain height to know as you look for those Sättigungskurgve that goes by the dew point (green dot ) at this altitude.

The relative humidity can be read (red dots) from the distance between the dewpoint (green dots ) and the Umgebungstemeraturkurve. The dew point, also referred to as "spread" is in fact a direct measurement of the relative humidity. If this is zero - in other words, to touch both curves, then the humidity is 100 %. The air is saturated. In general, the curves do not intersect, since the excess moisture in the form of fog condenses out, so that no saturation occurs.

In this example the temperature is 18 ° at the bottom of 95 ° F = 34 ° C at a dew point of 65 ° F = C. The dew point is equivalent to 16 K. This gives a relative humidity of about 40%.

Air layering

The air temperature decreases with increasing altitude mostly. If the opposite is the case, it is called an inversion. It can be in the vertical profile very easily recognize, namely when the temperature curve is significantly inclined to the right. ( In the example, no inversion is present. )

When the temperature with increasing altitude decreases more slowly than the trockenadiabatische temperature gradient, ie when the temperature curve is steeper than the guides on the Trockenadiabaten, one speaks of a stable stratification, in the opposite case of an unstable stratification. (If condensation occurs, instead Feuchtadiabaten are to be used. ) In the case of unstable stratification could be a parcel of air whose temperature is only slightly greater than the ambient temperature rise, without energy supply. In the graph, it would then follow the drying or Feuchtadiabaten until its temperature matches by adiabatic expansion with the ambient air. An unstable stratification would therefore facilitate the vertical exchange of air masses. A stable stratification and, in particular, an inversion but would slow down this rise very quickly.

In the picture you can see the highlighted area in the pink: The ambient temperature falls faster between about 2000 and 12000 m from than the Feuchtadiabate.

Cloud formation

Cumulus clouds form when moist rising warm air cools so far, until saturation is reached and the moisture contained condensed. This will happen under the following condition: a parcel of air (93 ° F here ) Just think at the bottom of certain temperature and follow the Trockenadiabaten the one hand and on the other hand Sättingskurve that (65 ° F ) passes through the dew point of this air package until both lines cut (blue triangle ). At this level (black dashed line) at which temperature (approx. 15 ° C) begins to condense the moisture. This altitude (about 2000 m) thus represents the lower edge of the clouds - the cloud base - dar.

The air can then continue to rise (see air layering ), but then follows the Feuchtadiabaten until it again reaches ambient temperature. For the formation of high clouds and thus the formation of thunderstorms is therefore a high instability and high absolute humidity in the soil air condition, as seen in this example. It can form cumulonimbus clouds with a cloud base of 2000 m, which extend to over 10 km in height.

Hairdryer

If moist air is deflected by a mountain up so it can get to cloud formation. The ascent is thus first trockenadiabatisch until the air reaches its saturation level, and then feuchtadiabatisch. Due to the precipitation of the air, water is removed. If the air then falls on the lee side of the mountain, it is usually compressed and warms up, but this time trockenadiabatisch. The air thus heated when it is sinking faster than it has been previously cooled during ascent. The temperature is in accordance with the overflow of the mountains therefore higher than before. This hot, dry wind makes itself felt as a hair dryer on the leeward side of the mountain.