Thurairajah Brentha, Cullens Chihoko Yamashita, Siskind David E, Hervig Mark E, Bailey Scott M
Center for Space Science and Engineering Research, Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, VA, USA.
Space Science Laboratory, University of California, Berkeley, CA, USA.
J Geophys Res Atmos. 2020 May 16;125(9). doi: 10.1029/2020jd032495. Epub 2020 Apr 17.
Using an 8-year (2007-2014) data set from two different limb-viewing instruments, we evaluate the relative roles of vertically versus obliquely propagating gravity waves (GWs) as sources of GWs in the polar summer mesosphere. Obliquely propagating waves are of interest because they are presumed to be generated by the summer monsoons. In the high-latitude upper mesosphere, the correlation coefficient between the time series of ice water content (IWC) and GW amplitude is 0.48, indicating that the observed GWs enhance polar mesospheric clouds (PMCs). For vertically propagating waves, the correlation coefficient between IWC and stratospheric/lower mesospheric (20-70 km) GW amplitude at the same high latitudes becomes more negative with increasing altitude. This change in correlation from negative in the lower mesosphere to positive at PMC altitudes suggests the presence of another source of GWs. The positive correlation coefficient between the time series of IWC and GW amplitude from 0-50°N, 20-90 km shows a slanted structure suggesting oblique propagation. This slanted structure is more robust in some seasons compared to others, and this interannual variability may be due to the latitudinal gradient of the mesospheric easterly jet where steeper gradients allow for low-latitude tropospheric GWs to be refracted to the high-latitude mesosphere more efficiently. Gravity-Wave Regional or Global Ray Tracer (GROGRAT) ray tracing simulations show that more GWs propagate obliquely compared to vertically propagating waves that reach PMC altitudes. For obliquely propagating waves, GROGRAT simulations indicate that nonorographic tropospheric GWs with faster phase speed (>20 m/s) and longer horizontal wavelength (>400 km) have a higher probability of reaching the polar summer mesosphere.
利用来自两种不同的观测仪器的8年（2007 - 2014年）数据集，我们评估了垂直传播与倾斜传播的重力波（GWs）作为极地夏季中层大气中GWs源的相对作用。倾斜传播的波之所以受到关注，是因为它们被认为是由夏季季风产生的。在高纬度上层中层大气中，冰水含量（IWC）时间序列与GW振幅之间的相关系数为0.48，这表明观测到的GWs增强了极地中层云（PMCs）。对于垂直传播的波，在相同高纬度地区，IWC与平流层/中层下部（20 - 70千米）GW振幅之间的相关系数随着高度增加而变得更负。这种相关性从下层中层大气中的负值变为PMC高度处的正值的变化表明存在另一个GWs源。从北纬0 - 50°、20 - 90千米处IWC时间序列与GW振幅之间的正相关系数呈现出倾斜结构，表明是倾斜传播。与其他季节相比，这种倾斜结构在某些季节更为明显，这种年际变化可能是由于中层东风急流的纬向梯度造成的，在该梯度较陡的地方，低纬度对流层GWs能够更有效地折射到高纬度中层大气。重力波区域或全球射线追踪器（GROGRAT）射线追踪模拟表明，与到达PMC高度处的垂直传播波相比，更多的GWs是倾斜传播的。对于倾斜传播的波，GROGRAT模拟表明，相速度更快（>20米/秒）且水平波长更长（>400千米）的非地形对流层GWs到达极地夏季中层大气的概率更高。
