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In the present communication, characteristics of mean winds and planetary waves in the mesosphere lower thermosphere (MLT) region during sudden stratospheric warming (SSW) events using observations from four meteor wind radars located at high, middle, low and equatorial latitudes are discussed. The response of the respective MLT regions to three SSW events that occurred during 2008–09, 2009–10 and 2011–12 winters are investigated. SSW signatures in the MLT zonal and meridional winds over the high latitude station Andenes ( 69. 3 ∘ N , 16. 0 ∘ E ) are found to have significant differences from event to event. Mean wind reversals in the high latitude MLT are found to be preceding the corresponding signatures at 60 ∘ N , 10 hPa by a few days. Zonal and meridional wind reversals extend to the MLT region over the mid latitude location Socorro ( 34. 1 ∘ N , 106. 9 ∘ W ). However, MLT region over the low latitude station Thumba ( 8. 5 ∘ N , 77 ∘ E ) as well as the equatorial station Kototabang ( 0. 2 ∘ S , 100. 3 ∘ E ) are found to be having a minimal response as far as mean winds are concerned. Apart from mean winds, planetary wave activity in the MLT region over the observational sites are examined, which show a systematic progression of planetary waves from high to equatorial latitudes during major as well as minor SSW events. To elucidate the origin of the observed planetary waves in the MLT region, the stratospheric winds are analyzed. Results suggest that the observed planetary waves have originated in the high-mid latitude middle atmospheric region. The present study provides observational evidence for secondary planetary wave generation in the high-mid latitude middle atmosphere and their equatorial propagation in the MLT as predicted by previous numerical modelling studies. Significance of the present study lies in employing a network of meteor radar observations to investigate the SSW signatures in the MLT region over high, middle, low and equatorial latitudes, simultaneously. [ABSTRACT FROM AUTHOR]

Stratospheric ozone attenuates harmful ultraviolet radiation and protects the Earth’s biosphere. Ozone is also of fundamental importance for the chemistry of the lowermost part of the atmosphere, the troposphere. At ground level, ozone is an important by-product of anthropogenic pollution, damaging forests and crops, and negatively affecting human health. Ozone is critical to the chemical and thermal balance of the troposphere because, via the formation of hydroxyl radicals, it controls the capacity of tropospheric air to oxidize and remove other pollutants. Moreover, ozone is an important greenhouse gas, particularly in the upper troposphere. Although photochemistry in the lower troposphere is the major source of tropospheric ozone, the stratosphere–troposphere transport of ozone is important to the overall climatology, budget and long-term trends of tropospheric ozone. Stratospheric intrusion events, however, are still poorly understood. Here we introduce the use of modern windprofiler radars to assist in such transport investigations. By hourly monitoring the radar-derived tropopause height in combination with a series of frequent ozonesonde balloon launches, we find numerous intrusions of ozone from the stratosphere into the troposphere in southeastern Canada. On some occasions, ozone is dispersed at altitudes of two to four kilometres, but on other occasions it reaches the ground, where it can dominate the ozone density variability. We observe rapid changes in radar tropopause height immediately preceding these intrusion events. Such changes therefore serve as a valuable diagnostic for the occurrence of ozone intrusion events. Our studies emphasize the impact that stratospheric ozone can have on tropospheric ozone, and show that windprofiler data can be used to infer the possibility of ozone intrusions, as well as better represent tropopause motions in association with stratosphere–troposphere transport. [ABSTRACT FROM AUTHOR]

With the recent increase in numbers of small and versatile low-power meteor radars, the opportunity exists to benefit from simultaneous application of multiple systems spaced by only a few hundred km and less. Transmissions from one site can be recorded at adjacent receiving sites using various degrees of forward scatter, potentially allowing atmospheric conditions in the mesopause regions between stations to be diagnosed. This can allow a better spatial overview of the atmospheric conditions at any time. Such studies have been carried out using a small version of such so-called multistatic meteor radars, e.g. Chau et al. (Radio Sci 52:811-828, 2017, 10.1002/2016rs006225). These authors were able to also make measurements of vorticity and divergence. However, measurement uncertainties arise which need to be considered in any application of such techniques. Some errors are so severe that they prohibit useful application of the technique in certain locations, particularly for zones at the midpoints of the radars sites. In this paper, software is developed to allow these errors to be determined, and examples of typical errors involved are discussed. The software should be of value to others who wish to optimize their own MMR systems. [ABSTRACT FROM AUTHOR]