The Study Of Quasi 30-day Oscillation At Middle And High Latitudes

Atmospheric oscillation is a global-scale perturbation existing in the middle and upper atmosphere.The oscillation and waves with different temporal and spatial scales play an important role in the circulation and thermal structure of the middle and upper atmosphere.So far,most studies on intra-seasonal oscillations(ISO)have focused on the ISO phenomenon in the tropical region,but few studies have investigated the ISO at mid and high latitudes.Relative to the extensive studies about the ISO in the tropics,the understanding of ISO in the mid-latitude region is still lacking,and its propagation characteristics,generation mechanism,and influence on the global atmospheric environment are still unknown.In this paper,we use the observations from a meteor radar at Beijing(40.3°N,116.2°E),a MST radar at Xianghe(39.8°N,116.5°E)and a radiosonde at Fairbanks(64.8°N,-147.9°W)and the European Centre for Medium-Range Weather Forecast(ECMWF)ERA-Interim reanalysis dataset to investigate the quasi 30-day oscillation activity during the 16 November 2013 to 28 February 2014 and 1 December 2010 to31 March 2011.And based on the ERA-Interim reanalysis dataset at Beijing,we analysis the propagation of quasi 30-day oscillation during 2013 to 2017.The main results are summarized as follows:1.Radar observations indicate that in the troposphere,the oscillation attains an amplitude peak in zonal wind at about 9km and propagates downward below 9km.At about 9-16 km,the oscillation gradually decays with height and then strengthens again as it propagates upward in the stratosphere.In the mesosphere,the oscillation obviously occurs at 78–86km with a maximum amplitude at 80 km.Reanalysis data show that in the troposphere,the oscillation propagates southward.At about 100(?16km)to 10(?32km)-h Pa levels,the oscillation is gradually reflected back to propagate northward,and then propagates poleward at higher altitude.Refractive index can explain its complex propagation characteristics very well.Consistence and coherence of its phase progression indicate that in the lower atmosphere,the oscillation comes from the polar region.Hence,ISOs can not only originate from but also propagate in the atmosphere at mid and high latitudes.2.Radiosonde observation from 1 December 2010 to 31 March 2011 indicates that quasi 30-day oscillations are worldwide ISO phenomenon,and are widespread in the troposphere and stratosphere.In the vertical direction,the oscillation propagates upwards,and reflection can also be observed in the troposphere at about 9km.And in the meridional direction,the oscillation generally propagates southwards,while near the 10-h Pa(?32km)level in the stratosphere the oscillation has tendency to propagate northwards.3.Statistical study at Beijing from 1 January to 2013 to 31 December 2017 shows that quasi 30-day oscillations occur almost in every winter,but the period of oscillation may fluctuate in different year.In the vertical direction,the oscillation propagates upwards,and the reflection phenomenon at 10 km can be clearly observed in the winter of 2013-2014.In the meridional direction,the reversal of the oscillation propagation from south to north occurs almost every winter,but the height of direction reversal varies with year.In addition,the filtering results in the latitudinal circle show that the quasi 30-day oscillation generally propagates westwards,but there are certain differences between years.