Previous: Introduction Next: Discussion Up: Ext. Abst.
Criteria for inertial gravity waves, gravity waves, shear and convection were developed to automate the analysis of radiosonde ascent data. Relationships of the different criteria to each othere were considered. Positive identification of shear as an inertial gravity wave generation mechanism is possible if the origin of the waves is indicated by the Stokes parameter method and when Stokes parameters indicate a rotation direction of the wind velocity vector opposite for the troposphere and the stratosphere. If there are waves travelling away from a jet then shear can be related to inertial gravity waves in the climatology. Positive identification of shear as a generator of gravity waves is more difficult. Many of the case studies indicate the presence of shear in conjunction with CAPE. In this case, the relative importance of the two effects is difficult to measure. For this reason, the climatological study of the following section includes the analysis of the subsets of data where CAPE and shear are mutually exclusive.
Necessary conditions for the identification of convection as dominant wave generation mechanism are an unstable troposphere where there is a potential for convection to happen. A method to do this is using the CAPE. Also there must be stable regions present in the atmosphere where gravity waves can develop. Since moderate convection exist in a great number of ascents there will be cases where this condition is fulfilled. If cases of gravity waves are detected and a high or moderate CAPE and the other wave generating mechanisms can be excluded then there is a high probability that these waves are caused by convection. However, other mechanisms often cannot be excluded, as has been found in case studies (not shown here).
A thunderstorm case study has shown that there is a link between CAPE and convection. Here the thunderstorm case was identified independently using sferics and a high level of CAPE detected simultaneously. Much more work has to be done to quantify this link. However the case studies have indicated an intrinsic problem with an automated climatology based on radiosonde ascents: the lack of an indicator to exclude orography or synoptic scale wave generation.
TG shows when the atmosphere can support waves but does not explain the cause. With the TG analysis, stationary waves are indicated if solutions with the observed wavelength exist. Stationary waves must be orographic as long as any convection or other generation mechanism did not produce stationary waves. Convective sources of stationary waves are possible as is suggested by the thunderstorm case. It is however not possible to apply the TG analysis to over 30000 profiles since it requires manual interpretation and can therefore only be used for individual cases.
An important wave generation mechanism, orography, cannot be identified automatically for the climatology. Therefore it has to be remembered that the wave cases may include orographically generated waves.
For the spectral analysis of the radiosonde data the results for the determination of the different criteria have been used to produce the energy density plots.