First observations of noctilucent clouds by lidar at Svalbard, 78°N

[摘要] In summer 2001 a potassium lidar was installed nearLongyearbyen (78° N) on the north polar island of Spitsbergen which is part of the archipelago Svalbard. At the same place a series of meteorologicalrockets ("falling spheres", FS) were launched which gave temperatures from the lowerthermosphere to the stratosphere. The potassium lidar is capable of detecting noctilucent clouds (NLCs) and of measuring temperatures in the lowerthermosphere, both under daylight conditions. In this paper we give an overview on the NLC measurements (the firstat this latitude) and compare the results with temperatures from meteorological rockets which have been published recently(Lübken and Mülleman, 2003) NLCs were observed from 12 June (the first day of operation) until 12 Augustwhena period of bad weather started. When the lidar was switched on again on 26 August, no NLC was observed. The mean occurrence frequencyin the period 12 June -- 12 August ("lidar NLC period") is 77%. The mean of all individual NLC peak altitudesis 83.6 km (variability: 1.1 km). The mean peak NLC altitude does not show a significantvariation with season. The average top and bottom altitude of the NLC layer is 85.1 and82.5 km, respectively, with a variability of ~1.2 km. The mean of the maximum volume backscatter coefficientb_maxat our wavelength of 770 nm is 3.9 x 10^-10/m/sr with a large variability of±3.8 x 10^-10/m/sr. Comparison of NLC characteristics with measurements at ALOMAR(69° N) shows that the peak altitude and the maximum volume backscatter coefficient are similar at both locations but NLCsoccur more frequently at higher latitudes.

Simultaneous temperature and NLC measurements are available for 3 flights andshow that the NLC layer occurs in the lower part of the height range with super-saturation. The NLC peak occurs over a large range of degree of saturation(S) whereas most models predict the peak at S = 1. This demonstrates that steady-stateconsiderations may not be applicable when relating individual NLC propertiesto background conditions. On the other hand, the mean variation of the NLC appearance with height and season is in agreement with the climatological variationof super-saturation derived from the FS temperature measurements.

[学科分类] 大气科学