Kaiming Huang

The interaction between the tropopause inversion layer and the inertial gravity wave activities revealed by radiosonde observations at a midlatitude station

The interaction between the tropopause inversion layer (TIL) and the inertial gravity wave (IGW) activities is first presented by using a high vertical resolution radiosonde data set at a midlatitude station, Boise, Idaho (43.57°N, 116.22°W), for the period 1998–2008. The tropopause-based vertical coordinate is used for the TIL detection, and for meticulously studying the IGW variation around the TIL, the broad spectral method is used for the IGW extraction. Generally, the TIL at the midlatitude station is stronger and thicker in winter and spring, which is consistent with previous studies. Our study confirmed the intense interaction between the TIL and IGW. It is found that the TIL not only could inhibit the upward propagation of IGWs from below but also imply the possible excitation links between the TIL and IGW. The results also indicate that the enhanced wind shear layer just 1 km above the tropopause may result in instability and finally leads to the IGW breaking and intensive turbulence. Subsequently, the IGW-induced intensive turbulence leads to strong wave energy dissipation and a downward heat flux. This downward heat transportation could significantly cool the tropopause, while it has only negligible thermal effect on the atmosphere above the tropopause. Then, the IGW-induced cooling at the tropopause makes the tropopause colder and sharper and finally forms the TIL. These suggest besides previously proposed mechanisms that IGWs also contribute greatly to the formation of TIL, which is consistent with a recent related simulation study.

Planetary wave characteristics in the lower atmosphere over Xianghe (117.00°E, 39.77°N), China revealed by the Beijing MST radar and MERRA data

Using observation data from the Beijing MST radar from December 2013 to November 2014, together with the MERRA data, the dominant planetary waves (PWs) in the lower atmosphere over Xianghe (117.00°E, 39.77°N), i.e., quasi-16-day and quasi-10-day oscillations, were identified and investigated. These two kinds of PWs displayed similar seasonal and height variations, indicating they may have similar generation sources and dissipation processes. For both of them, near the tropospheric jet, significant zonal amplitudes could be observed in winter and spring months; quasi-constant phase or partial vertical wavelength larger than 100 km was present in the zonal wind in December, March and April, indicating they were quasi vertical stasnding waves near the tropospheric jet. The calculated refractive indexes of these two PWs were significantly negative in the lower troposphere (3.5-5 km) and near the tropopause (15-20 km), and the resulted strong wave evanescence or even wave reflection could explain the observed quasi standing structure of these two PWs and height variations of their wind amplitudes. Their estimated zonal wavenumbers in every month both showed the prevailing eastward propagation. Furthermore, we investigated the impact of PWs on the background wind by E-P fluxes and divergences, which indicates that both the quasi-16-day and the quasi-10-day PWs, especially the latter, may contribute significantly to the construction and maintenance of the tropospheric jet. We also found that the tropospheric jet magnitude and height were both intensively modulated by the quasi-16-day and quasi-10-day PWs.

Double sporadic metal layers as observed by co-located Fe and Na lidars at Wuhan, China

In this paper, we report a set of double sporadic layer events observed by Fe and Na lidars over Wuhan, China. The two sporadic metal layers above normal layer were named as upper and middle sporadic metal layers, respectively. In these events, the upper, middle and normal Fe layers presented altitude separately. There were nine double sporadic Fe events observed in 163 nights during 2010-2013. Eight of the nine events were observed in summer. The maximum ratios of peak density for upper and middle sporadic Fe layers to normal Fe layer were up to ~375% and ~225%, respectively. The peak altitudes of upper (middle) sporadic Fe layers were in the range of 102-107 km (95-98.5 km). The double sporadic Fe layers lasted more than 2 hours. Interestingly we found density enhancement occurred simultaneously in upper, middle and normal Fe layers on two events. On the nine Fe events, there existed five nights of co-located Na lidar observations. We found double sporadic Na and Fe layers simultaneously appeared. They presented similar structures, altitudes and temporal variations in all five compared events. A little different from Fe, the middle sporadic Na layer was not separated with Na main layer maybe for the wide altitude range of Na main layer. The ratios of upper (middle) sporadic Fe and Na peak values were in the range of 6.6-52 (0.57-6.58). While the exact formation mechanism responsible for double sporadic metal layers is still unclear, some possible explanations and corresponding observations are discussed.

A mechanism to explain the variations of tropopause and tropopause inversion layer in the Arctic region during a sudden stratospheric warming in 2009

The mechanism to explain the variations of tropopause and tropopause inversion layer (TIL) in the Arctic region during a sudden stratospheric warming (SSW) in 2009 was studied with the Modern-Era Retrospective analysis for Research and Applications reanalysis data and GPS/Constellation Observing system for Meteorology, Ionosphere, and Climate (COSMIC) temperature data. During the prominent SSW in 2009, the cyclonic system changed to the anticyclonic system due to the planetary wave with wave number 2 (wave2). The GPS/COSMIC temperature data showed that during the SSW in 2009, the tropopause height in the Arctic decreased accompanied with the tropopause temperature increase and the TIL enhancement. The variations of the tropopause and TIL were larger in higher latitudes. A static stability analysis showed that the variations of the tropopause and TIL were associated with the variations of the residual circulation and the static stability due to the SSW. Larger static stability appeared in the upper stratosphere and moved downward to the narrow region just above the tropopause. The descent of strong downward flow was faster in higher latitudes. The static stability tendency analysis showed that the strong downward residual flow induced the static stability change in the stratosphere and around the tropopause. The strong downwelling in the stratosphere was mainly induced by wave2, which led to the tropopause height and temperature changes due to the adiabatic heating. Around the tropopause, a pair of downwelling above the tropopause and upwelling below the tropopause due to wave2 contributed to the enhancement of static stability in the TIL immediately after the SSW.