Polar mesospheric horizontal divergence and relative vorticity measurements using multiple specular meteor radars. Issue 7 (1st July 2017)

• Record Type: Journal Article
• Authors: Chau, Jorge L.; Stober, Gunter; Hall, Chris M.; Tsutsumi, Masaki; Laskar, Fazlul I.; Hoffmann, Peter
• Is Part Of: Radio science. Volume 52:Issue 7(2017:Jul.)
• Page Start: 811
• Page End: 828
• Publication Date: 2017-07-01
• Subjects: MLT dynamics -- horizontal divergence -- relative vorticity -- polar mesosphere -- vertical wind; Radio meteorology -- Periodicals; Radio wave propagation -- Periodicals; 621.38405
• DOI: 10.1002/2016RS006225
• Languages: English
• ISSNs: 0048-6604

Abstract

Abstract: We present the first horizontal divergence and relative vorticity measurements at polar mesospheric altitudes measured from the ground. Our technique relies on combining information from two specular meteor radars (SMRs) separated 130 km at polar latitudes, specifically, the Andenes and Tromsø radars in northern Norway. The resulting values are obtained over a region that spans an approximate area of 400 km diameter at mesospheric altitudes. The temporal and vertical resolution are 1 h and 2 km in altitude. The technique not only allows to obtain the gradient terms of the horizontal wind, that in turn are used to derive the horizontal divergence and relative vorticity, but also improves the horizontal sampling compared to single SMRs. Synthetic data are used to qualitatively test the technique and identify potential sources of biases on the resulting measurements. For example, we have found that an apparent large mean vertical velocity is obtained, after averaging many days, if there is a persistent divergent field. We present a climatology of the resulting wind field parameters from 12 years of continuous observations and focus on the summer results. We found a persistent altitudinal pattern in both the horizontal divergence and relative vorticity fields during all northern hemispheric summers. The horizontal divergence is mainly positive decreasing in magnitude below ∼86 km, and the relative vorticity is negative/positive below/above ∼88 km over northern Norway. Plain Language Summary: We present a novel approach to measure new parameters of the wind field at altitudes between 80 and 100 km at polar latitudes. The approach consists of using closely located radars. These radars measure the winds from observing the time evolution of meteor trails. Since the echos from meteor trails are strong, the radars used are relatively small. We have analyzed data from radars in northern Norway that have been operating for more than 12 years. This is the first time that such data sets are combined to explore new parameters like horizontal divergence and relative vorticity. The climatology of this new parameters shows that there are persistent and well‐identified patterns at the polar summer mesosphere. We expect that the new parameters will be useful in future efforts to improve the understanding of processes in this part of the atmosphere. Key Points: First direct measurements of mesoscale horizontal divergence and relative vorticity in the polar MLT region The height transition from negative to positive horizontal divergence in the polar summer indicates the height of maximum mean vertical wind The transition height of horizontal divergence is slightly higher than for the relative vorticity in the polar summer mesosphere