Heat bubble over flat terrain
A well known test case for microphysics schemes is a heat bubble over flat terrain. We have
used this bubble for testing both, the warm and the mixed phase microphysics scheme having been
implemented in LM-SPECS, using the following setup:
Initialization of atmosphere by idealized initial sounding after Weisman and Klemp .
Initial temperature disturbance of up to 2 K.
80x80 gridpoints, horizontal resolution 1 km.
48 vertical layers, model top 18 km, resolution about 90 m near ground up
to 600 m near top.
The initial wind was set to zero.
The applied temperature disturbance leads to the development of a deep convective cloud which
heavily precipitates after a while. The picture to the right shows results from sensitivity
studies with respect to the initial number concentration of aerosols (numbers to the right,
denoted in cm-3
) and with respect to the heterogeneous ice nuclei type (see top of the
diagrams). The solid black lines refer to the total liquid water content (the sum over the
whole spectrum including rain drops) and the coloured contours refer to the total ice water
To the right and further below, mass spectra resulting from the warm case are shown
for three different heights and three different times. At 12 minutes, only cloud droplets are
present. After 24 minutes, rain drops start to form, especially in higher regions. The onset
of rain drop formation for the most polluted case is delayed. After 36 minutes, all three
cases precipitate heavily.
The resulting accumulated rain from the warm cases below the center point of the clouds is
illustrated in the diagram to the left. The initial aerosol number density has a significant
influence on the amount of precipitation - the cleanest case precipitates most, the most
polluted precipitates least. This points to the importance of considering aerosol particles
when it comes to a correct parameterization of rain formation.
The results of this studies have been submitted to Atmospheric Research (see Publications
 Weisman and Klemp (1982), Mon. Wea. Rev., 110, 504-520.