Diagnosis of Local Gravity Wave Properties during a Sudden Stratospheric Warming

Commonly, wave quantities are maintained in zonal mean averages. Hence, local wave phenomena remain unclear. Here, we introduce a diagnostic tool for studies of wave packets locally. The "Unified Wave Diagnosis" (UWaDi) uses the Hilbert Transform to obtain a complex signal from a real-valued function and estimates the amplitude and wave number locally. Operational data from the European Centre for Medium-Range Weather Forecasts is used to perform the analysis. Restrictions on gravity wave propagation due to model sponge layers are identified well above the 10 hPa altitude. From a minor stratospheric warming in January 2016 three cases for vertical gravity wave propagation in different background wind conditions are selected. It is shown that zonal mean wind quantities cannot reveal local "valves" allowing gravity waves to propagate into the mid-stratosphere. The unexpected finding of high gravity wave activity at the minor warming of 30 January 2016 is related to strong planetary wave activity and a strong local "pump". Accordingly, the advantages of a local wave packet analysis are demonstrated for profiles up to the model sponge layer.