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Berlin Environmental Atlas

04.10 Climate Model Berlin - Analysis Maps (Edition 2003)

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Map Description / Supplementary Notes

In the following, extensive additional information is provided on the dynamics and significance of the cold-air balance of open areas, with selected examples. The text completes the contents of the chapter Map Description.

Cold-Air Producing Open Areas and their Effect on Built-Up Areas

In Fig. 7, 3 locations are identified, which are to provide an example for discussing in a more detailed manner the cold-air balance on the basis of a selected corridor section of 9 grid cells of 1600 m of section length (200 m grids), and of 450 m (50 m grids), respectively. For the characterization of the dynamics of the cold-air balance, these examples were placed along the boundary area of cold-air-generating open areas and built-up areas. For an overall comparison of the values within the 200 m grid, a mean grid cell value was then determined based on the cells along the corridor section.

As examples of the compensation of open areas, transition zones were used: from Grunewald to Wilmersdorf (A) and in the Mahlsdorf (B) neighborhood on the eastern outskirts of Berlin. The southwestern section of Tempelhof Airport (C) represents the detailed-analysis area in which a higher-resolution 50 m grid was used.

Figure 7 - Thumbnail
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Fig. 7: Situation of the test areas A, B and C for the clarification of the processes "cold air generation" and "cold-air out-flow" during a low-exchange cloudless summer night (10 PM; grid resolution: 200 m)

Example: Grunewald Forest

With over 3000 hectares, the Grunewald forest is among the largest wooded areas in the city area. Along a corridor of approx. 11 km, parts of the Boroughs of Charlottenburg-Wilmersdorf and Zehlendorf-Steglitz, located to the east of the forest, profit particularly from the high cold-air productivity. Fig. 8 shows the transition zone from the Grunewald to the detached-home areas in Wilmersdorf; here, the air interchange per grid cell and hour is relatively high, with exchange rates of over 20.

Figure 8 - Thumbnail
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Fig. 8: Air exchange per grid cell and the autochthonous current field in the Grunewald-Wilmersdorf transition zone during a low-exchange cloudless summer night (10 PM; grid resolution: 200 m)

The correspondingly long range of the cold-air current is most strongly in evidence in Wilmersdorf at 10 PM, with up to 3000 m, which is due to the low-density detached-home structure of the area. In Steglitz, by contrast, a value of only approx. 1500 m is achieved, due to the increasing density of the built-up area. At 6 AM, the cold air only penetrates approx. 1000 to at most 2200 m into the built-up area.

For the 1600 m long section, the mean value of the air exchange per grid cell, the mass current as well as the flow speed of the corridor wind were exemplarily calculated (cf. Table 3). This corridor starts at Auerbachstrasse at the AVUS Freeway, and leads across Regerstrasse to Waldmeisterstrasse.

A decrease of the mean grid cell value over the course of the night is apparent. The air-exchange rate declines by approx. 30%, from 20.13 to 13.99. The same applies to the mass current, which is reduced by approx. 25%. The drop in current speed of the corridor wind is still more strongly apparent, at approx. 64%.

et410_03
Tab. 3: Mean air-exchange rate, mass current and flow speed of the corridor wind per grid cell along the corridor section in the Grunewald-Wilmersdorf transition zone during a low-exchange cloudless summer night (grid resolution: 200 m)

Excel
[This table is also available in Excel format (MS Excel is required).]

Example: Mahlsdorf

The cold-air source area for this example is the open area adjacent to and north of the Dahlwitz forest. It stands out considerably from the built-up areas, with air exchange rates of over 20 per grid cell and hour (cf. Fig. 9).

The range of this air movement around 10 PM is between 1100 m north of the Federal Highway 5 in the area of the rapid-rail line (S-Bahn) and 1800 m toward Hönower Damm. There, it unites with the corridor wind from the Kaulsdorf Busch and flows northward, where the wind speed finally drops to below 0.2 m/s at the Mahlsdorf rapid-rail station.

The penetration depth remains almost unchanged until 6 AM. Only the flow direction changes, toward the southwest.

Figure 9 - Thumbnail
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Fig. 9: Air exchange per grid cell and autochthonous current field in the Mahlsdorf area during a low-exchange cloudless summer night (10 PM; grid resolution: 200 m)

Except for the mass current, the mean grid-cell values surpass those of the area Wilmersdorf(A) slightly (cf. Tab. 4). However, the essential difference is the weaker drop in the characteristic values until the early morning.

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Tab. 4: Mean air exchange rate, mass current and flow speed of corridor wind per grid cell along the corridor section in Mahlsdorf during a low-exchange cloudless summer night (grid resolution: 200 m)

Excel
[This table is also available in Excel format (MS Excel is required).]

Example: Tempelhof Airport

Here too, analogously to the investigation areas already described, the situation was examined along a selected corridor section of 9 grid cells. In this case, the southwestern part of Tempelhof Airport served for the analysis of the cold-air balance in the detailed-analysis area, where a 450 m long section along Tempelhofer Damm was selected (cf. Fig. 10). For the analysis of air exchange per grid cell/hr., the longitudinal distance that the air-mass flows through is decisive. To make a comparison possible between the two grid intervals, the cell value of the 50 m grid must therefore be divided by 4, to make it comparable with the 200 m value.

Figure 10 - Thumbnail
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Fig. 10: The air exchange per grid cell and autochthonous current field in the area of Tempelhof Airport during a low-exchange cloudless summer night (10 PM; grid resolution: 50 m)

With regard to the air change rate, two areas with relatively high hourly air exchange rates of over 80 per grid cell are recognizable in the airport area, including its apron area, and the intersection of Tempelhofer Damm and the A 100 freeway. In reference to the 200 m grid, which was used for the urban area, this corresponds to a cell value of 20, and is comparable to the example Wilmersdorf (A), in terms of the characteristic value. Despite the high air-exchange rate, even in terms of broad extent, the generation of the corridor wind in the apron area is impaired by the air terminals both at 10 PM and at 6 AM. The incorporation of the structural heights into the calculation grid for the FITNAH simulation yields a mean structural height, with the result that the air flow can pass over single obstacles which are nominally higher than 5 m.

By contrast, a corridor wind which, with a western current along the freeway A 100 and a length of at most 450 m, is rather weak by comparison with the other locations, can develop along the corridor section observed at 10 PM. At this time, it is juxtaposed to an eastward cold-air current from the allotment-garden colonies of the Schöneberg South Terrain. To a certain extent, Manteuffelstrasse functions as the separation line between these two corridor winds.

By 6 AM, the latter corridor wind from the allotment-garden area has come to a virtual standstill, while the range of the corridor wind starting from Tempelhof Airport has doubled to approx. 800 m and penetrated up to 200 m to the south to Tempelhofer Damm (cf. Fig. 10).

Table 5 summarizes the results for the part of the core area observed. It is clear that the calculated values have increased slightly over the course of the night, and thus demonstrate a different trend from areas (A) and (B). This is due to the high spatial resolution of the 50 m grid, which shows a shift of the grid cells with a high air exchange rate toward the built-up area.

et410_05
Tab. 5: Mean air-exchange rate, mass current and flow speed of the corridor wind per grid cell along a corridor section in the Tempelhof Airport area during a low-exchange cloudless summer night (grid resolution: 50 m)

Excel
[This table is also available in Excel format (MS Excel is required).]

For the area to the west of the observed corridor section and the area adjacent to it in the direction of flow of the corridor wind, the cold-air volume was determined on the basis of the air exchange. The grid cells covering an area of approx. 20 hectares adjoining the corridor section to the west of the airport and for which a wind speed of > 0.2 m/s could be proved have been taken into account.

The height of these near-ground grid cells is 5 m, which yields a volume of 12,500 m³ per cell. For the stated area, an hourly air exchange of 5.52 million m³ can be estimated. For this segment, projected to a nighttime period of 8 hours, this yields an air exchange induced by the cold-air generation of the airport near-ground layer of air (up to 5 m above ground) of a total of 43.36 million m³.

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