Insects in the evening and birds in the night as winds
Matti Leskinen 1998-01-21
The direction (dashed) and speed determined using the Doppler weather radar echos. Direction is given as a deviation from north so that -45° means flow from the northwest.
Only the result at 17:50 local summer time can be considered as a wind sounding, since then the echo was caused by insects drifting with the wind. Measurements in the night were mostly based on echos from migrating birds, and the results represent the mean direction and speed of bird migration.
If it is assumed that the direction and speed based on insect echos is a good approximation of wind in the night, the direction and speed of birds in reference to air can be calculated. So the headings and airspeeds of birds could be estimated.
At 00:20 two distictly different layers can be found:
- at about 500 meters AGL
- wind from NW at 10 m/s
- birds from N at 18 m/s
- the heading of birds to SW at an airspeed of 13 m/s
- noin 1500 m korkeudella
- wind 10° to N from 10° NW at 10 m/s
- birds 10° to E from N at 10 m/s
- birds had headings along the Finnish coastline to west at an airspeed of 8 m/s
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