Abstract
Abstract. The characteristics of dynamical and thermal structures and inertial gravity waves (GWs) in the troposphere and lower stratosphere (TLS) over Yichang (111°18´ E, 30°42´ N) were statistically studied by using the data from intensive radiosonde observations in August 2006 (summer month) and January 2007 (winter month) on an eight-times-daily basis. The background atmosphere structures observed in different months exhibit evident seasonal differences, and the zonal wind in winter has a prominent tropospheric jet with a maximum wind speed of about 60 ms−1 occurring at the height of 11.5 km. The statistical results of the inertial GWs in our two-month observations are generally consistent with previous observations in the mid-latitudes. In the summer month, the mean intrinsic frequency and vertical wavelength of the inertial GWs in the troposphere are still larger than those in the lower stratosphere with the absence of intensive tropospheric jets, suggesting that the Doppler shifting due to the tropospheric jets cannot completely account for the differences between the GWs in the troposphere and lower stratosphere. Compared with the observations in the summer month, some interesting seasonal characteristics of the GWs are revealed by the observations in the winter month: 1) more and stronger tropospheric GWs are observed in the winter month; 2) less and weaker GWs are observed in the lower stratosphere in winter; 3) the ratio of the mean GW kinetic energy density to potential energy density is smaller than 1 in winter, which contrasts to that in summer. Most of the seasonal differences can be explained by the intensive tropospheric jets in winter. In both the summer and winter months, the fitted spectral slopes of the vertical wave number spectra for GWs are generally smaller than the canonical spectral slope of −3. Correlation analyses suggest that the tropospheric jet induced wind shear is the dominant source for GWs in both the troposphere and lower stratosphere. Moreover, the tropospheric (lower stratospheric) GWs are found to be modulated by the quasi-7-day (10-day) PW, and the impacts of the diurnal tide on the GWs are relatively weak.
Highlights
The lower atmosphere is frequently disturbed by atmospheric waves, including gravity waves (GWs), tidal waves and planetary waves (PWs)
It is widely accepted that GWs in the middle and upper atmosphere (MUA) play an important role in determining the local and global dynamical and thermal structures of the MUA (Lindzen, 1981; Holton, 1982, 1983; Fritts and Vincent, 1987)
It has been estimated that on a monthly average GWs provided forcing on the order of 100 ms−1 day−1, which is responsible for the wind reversal around the mesopause and the cold summer mesopause (Lindzen, 1981), and they are partly responsible for driving the Mesospheric Semi-Annual Oscillation (MSAO) (Dunkerton, 1982)
Summary
The lower atmosphere is frequently disturbed by atmospheric waves, including gravity waves (GWs), tidal waves and planetary waves (PWs). It is noteworthy that since the temporal intervals of the twice daily radiosonde routine measurements are usually 12 h, neither the diurnal variations of the dynamical and thermal structures of lower atmosphere nor the short-term (with time scale no longer than 1 wave period) evolutions of GWs can be revealed by these observations. Aiming at further investigation of the lower atmospheric dynamics, especially the lower atmospheric waves and their interactions, a two-month (August 2006 and January 2007) radiosonde observation campaign was launched by Wuhan University. Compared with the routine radiosonde observation (based on twice daily measurements) made by meteorological agencies, the data from this campaign have a shorter time interval, which permits us to study the propagation and evolution of inertial GWs, tides and PWs. In the presented paper, we focus primarily on GW activity in the TLS. We give a brief summary of our observations
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
