Drifting of Aerosol Structures

This example shows the drift of aerosol „plumes“ over Munich. Horizontal lidar measurements over a time period of 15:16 min are shown, with a temporal resolution of 5 seconds (May 16., 2001). The wavelength is 532 nm.

Figure 1
Fig. 1: Horizontal lidar measurements

The horizontal axis shows the time, starting at 09:28:38 hours, the vertical axis shows the distance from the lidar up to 4.8 km with the lidar at the bottom of the figure. The slope of the aerosol structures result from the drifting of aerosol plumes with the wind.

In Fig. 2 shows the corresponding wind field (speed and direction), measured at the institute's meteorological station which is next to the lidar site at the top of our building. The time of the lidar measurements are highlighted by the blue lines. The wind direction was 270 degree (west wind to the east; right scale) and the wind speed was in the range of 3 m/s (left scale), but varying between 2 m/s and 5 m/s.

Figure 2
Fig. 2: Wind field at the lidar site; the time of the lidar measurements is indicated by the blue lines

In the next figure (Fig. 3) we show a map of central Munich: The lidar site is marked by the red circle. The red line indicates the direction of the lidar measurement, the distances of 500 m and 1500m are marked by the short ticks, the long tick indicates 1 km distance from the lidar. The wind direction is illustrated by the yellow line. The angle between the two directions is approximately 22 degrees, that means that the wind component in the direction of the lidar's line of sight was about 2.8 m/s on average.

Figure 3
Fig. 3: Line of sight of the lidar measurement (red) and wind direction (yellow)

In the final figure (Fig. 4) we show the estimated wind velocity from the drifting of the aerosol plumes. They agree very well with the meteorological data. They also show the variability/inhomogeneity of the wind field. Typical values can be seen if you move the cursor on the figure.

Fig. 4: Horizontal lidar measurements