Content

Temperature and Moisture Conditions in Medium Low-exchange Nocturnal Radiation Periods 1992

Methodology

Due to the differences in available data, the climate parameters were calculated separately for West Berlin and East Berlin/surrounding countryside. However, the calculation procedures were with largely identical. Since all calculation steps had to be conducted for East Berlin and the surrounding countryside, the procedure will be outlined briefly using the example of parameter temperature.

Of central importance for the different calculation steps is the assignment of individual measuring points to continuously measuring climate stations and/or to measuring points which were repeatedly visited during the measuring trip. In addition, it was assumed that the temperature course at the climate station and/or the repeatedly visited measuring points could be carried over to other measuring points.

Using this assignment, the different measurements from an excursion could be synchronized, i.e. collated with others at a given point in time (see Stülpnagel 1987). Subsequently the results from the measuring trips were averaged for each measuring point. For weighting of the individual trips, the weather statistics from May – September 1991 for Berlin – Dahlem were applied (Institute for Meteorology of the FU – Berlin 1991): The individual measurements were weighted as to the wind direction, wind speed and the degree of overcast at the measuring time and its proportional effect on the weather conditions during all low-exchange nocturnal radiation periods in the period May to September.

To derive the mean conditions in low-exchange nocturnal radiation periods in the summer semester 1991 from the results of the measuring trips, again results from the climate stations were applied. The sorting of the measuring points from each of the measuring trips into the corresponding climate station structure was done step by step according to a procedure described in detail by Stülpnagel 1987. It can only be described briefly here.

First, the measuring points adjacent to a climate station were considered. Regression equations were developed empirically in order to derive the temperature of the climate station at the adjacent point. The data from each measuring trip was compared with the contemporaneous data of the station and as a linear function of the temperature difference of the station to the central station Tiergarten at this point in time. The adjacent measuring points for the period under examination can be projected using these equations.

Thus a network of ”fixed points” emerged which could be used for the projection of the remaining measuring points. Thus measuring routes which passed several climate stations, for which several fixed points emerged, were broken down into lines extending from one fixed point to the next. The projection for the intermediate measuring points was calculated by carrying over the measured temperature course between the fixed points and the measuring points to be calculated onto the projected course at the fixed points. That means it was assumed, that at a expansion or compression set for the temperature at the fixed points a corresponding expansion or compression set is to be made. This process was expanded gradually to all further measuring points, whereby common points were treated with an already adjusted expansion as new fixed points.

At the conclusion of the process, the extrapolated temperatures for each measuring point of each line had been calculated for the investigation period. The wide-area depiction was obtained by way of manual interpolation taking into account the area use (SenStadtUm 1993b, c).

The projections for the relative humidity and the vapor pressure, which were needed for calculation of the equivalence temperature, were generated analogously.

For the western part of the city the temperature distribution under low exchange weather conditions was essentially carried over from the first edition of the Environmental Atlas. However the temperature level was lowered by about 1 °C. This emerged through a comparison of the mean values for the summers 1982 and 1991 at the climate station in Berlin-Dahlem and the assumption that a general reduction in this amount for all measuring points is justified. The only deviations from this procedure were for the new measuring trips when they crossed into areas of West Berlin.