User`s manual

6 ATMOSPHERE AND INSTRUMENTS
6.7 Convection forecast
If the glider is equipped with an outside temperature and humidity probe, a simple convection
forecast system estimates the convection ceiling and the cloud base. The humidity probe is optional
and is mainly required for estimating cloud base.
Prior to takeoff or during flight the pilot can modify the maximum forecast temperature on the ground
by adjusting the value in Basic Settings described in subsection 5.4.
The forecast convection ceiling is determined by the altitude at which the atmospheric temperature
equals the maximum forecast temperature on the ground, cooled adiabatically as it rises according
to the dry adiabatic lapse rate. Typically the glider will not climb as far as the convection ceiling
and so the measured values are extrapolated to find the ceiling. If the atmosphere is stable, the
convection ceiling is reported as zero altitude.
The forecast cloud base is determined by the altitude at which the dew point intersects the max-
imum forecast temperature on the ground, cooled adiabatically as it rises according to the dry
adiabatic lapse rate. If no clouds are forecast, the cloud base is reported as zero.
6.8 Analysis dialog: Wind, Temperature, Barograph and Climb his-
tory
Analysis is used to see several aspects of the atmosphere. It is accessed via the menu under:
INFO  Analysis Show
Several pages are of interest:
• Wind at altitude This shows a graph of the wind speed versus height, and shows the wind vector
at several heights.
Set wind opens Wind Settings (e.g. to manually set the wind).
XCSoar Manual (Altair version) • XCSoar-A-EN 62