Stratocumulus clouds – A summary

Robert Wood (University of Washington, Seattle, Washington) has written a very nice overview article on Stratocumulus clouds referring to their climatology, their dynamics and microphysics. The paper was published in Vol. 140 (p. 2373-2423) of Monthly Weather Review. The paper can be downloaded at here:

In the following i want to sum up some of the most interesting facts Robert Wood lists about Stratocumulus clouds. I reordered the information in a slightly new way. All the references can be found below.


Dewpoint calculation script in Python

Using the well-known approximation to calculate the dew point temperature from the actual temperature and the relative humidity, it is very easy to write a small script that can do this calculation for us.

I choosed Python to do this job. Feel free to use this script for your own purposes:

import sys
import numpy as np
# approximation valid for
# 0 degC < T < 60 degC
# 1% < RH < 100%
# 0 degC < Td < 50 degC 
# constants
a = 17.271
b = 237.7 # degC
# sys.argv[0] is program name
def dewpoint_approximation(T,RH):
    Td = (b * gamma(T,RH)) / (a - gamma(T,RH))
    return Td
def gamma(T,RH):
    g = (a * T / (b + T)) + np.log(RH/100.0)
    return g
Td = dewpoint_approximation(T,RH)
print 'T, RH',T,RH
print 'Td=',Td

The script expects two input parameters. First the temperature (in °C) and second the relative humidity (in %).

Fog in satellite images

Winter last year i stumbled over a satellite image product at I don’t know how the cloud mask on this site is created but it seemed to have a problem with fog. Looking at this image only one gets the impression that there are absolutely no clouds over Germany. Looking into the sky proves that it is foggy. So this cloud mask could be a little bit misleading when used for example for estimating temperatures.

But how can this difference of observation and product be explained?