Observation And Studies On The Lower Mesospheric Inversion Layers Over Beijing

There have been few observations of lower Mesosphere atmosphere temperature above Beijing. The Mesospheric Inversion Layer(MIL) is an inversion layer of ~10 km thick vertically within the lower mesosphere at equatorial and mid-latitude regions which always shows positive temperature gradient at the bottom of the layer. Since first reported 40 years ago, MIL has been frequently observed with a variety of sensing instruments. This phenomenon occurs quite often in the mid-latitude winter hemisphere, and is observed to have a broad horizontal distribution on scale of thousands of kilometers. This phenomenon greatly affects the middle atmosphere dynamics by affecting the atmosphere stability, vertical mixing and energy transfer. MILs are mostly noticed in two different altitude regions, ~70 km(lower MILs) and ~95 km(upper MILs). Lower MILs can be observed by Rayleigh lidar and satellite measurements. The characteristics of the lower MIL over Beijing are studied for the first time in this paper.The data source is the observation data of the Rayleigh Lidar located in Yanqing(40.47°N, 115.97°E), Beijing from January to February in 2012 and from May 2012 to April 2013. Details about the principle of Rayleigh Lidar system, data retrieval method and error analysis are introduced in this article. With multiple data filtering, incorrect data caused by weather condition, errors and instrument accuracy was excluded and temperature information of 141 nights in the height range of 60-80 km above Beijing was selected. The height resolution is 384 m and time interval is 25 min.The lower Mesospheric Inversion Layers were statistical analyzed in this article.According to the temperature profiles of 141 nights, 92 lower MIL events were obtained over Beijing. Their mean inversion amplitude is 23.4K; the mean thickness is 4.78km; and the mean height of the bottom is 68.2km. The lower MIL whose vertical scale is 3km has quite high occurrences and higher inversion amplitude and consequently shouldn’t be omitted in analysis. Besides, no lower MIL whose vertical scale over 10 km has been detected.Lower MILs with inversion amplitude larger than 25 K mostly was detected in winter and the maximal inversion amplitude was observed in winter, too. The lower MIL whose inversion amplitude is larger than 25 K have been found to occur least in Spring and Summer and relatively more in Autumn. Vertical propagating was observed within about 2/3 of the lower MILs. Among all vertical propagating events, 47 of them were downward and 12 of them were upward. In 3 special lower MILs, the propagating direction changes from downward to upward.Furthermore, 6 double low-level MILs were observed, 3 of which propagate vertically. During the double lower MIL of 17 th May. 2012, the lower MIL was dissipating and the upper MIL was spreading. Meanwhile, the upper MIL and the lower MIL propagates downward with vertical speed of 610m/h and 460m/h respectively. And during the double lower MIL observed on 8th Feb. 2013, the upper MIL was dissipating and the lower MIL was spreading. The upper spread upward while the lower spread downward with vertical speed of 512m/h and 263m/h respectively. However, during the double lower MIL on 18 th Feb. 2013, the lower MIL was spreading downward with a speed of 1300m/h with inversion amplitude increasing. After the amplitude reached its maximum value, a weak shallow upper MIL was split out from the MIL. Hours later two MIL dissipated simultaneously. The speed of MILs’ vertical spread varies tremendously and further analysis about its physical mechanism is still needed. We refer its vertical spread speed difference might be related to regional gravity wave.After collecting and systemizing Lower MILs above Beijing and comparing the result with other researches this paper reports the characteristics of MILs above Beijing for the first time. Besides, data detected by Meteor Radar in Fuke(19°7′N, 109°7′E), Hainan and Na Fluorescence Lidar in Haikou(19°30′N, 109°5′E) is systemized too. A mesospheric gravity wave with 8km vertical wavelength was observed by both instruments and was analyzed primarily.