Anticyclonic Rossby wave breaking (AWB)-associated vertical wind shear anomalies, 1979-2019
This repository comprises data generated for the study "Winter Rossby Wave Breaking Persistence in Extended-range Seasonal Forecasts of Atlantic Tropical Cyclone Activity" (Jones et al. 2021). The repository includes: i) The first four leading modes of tropical Atlantic vertical wind shear (seasonal); ii) Six-hourly (0Z, 6Z, 12Z, 18Z), monthly and seasonal indices of vertical wind shear anomalies associated with the downstream edge of anticyclonic Rossby wave breaking (AWB) detected over the North Atlantic region (20-40N, 100-5W); iii) An index of subtropical zonal wind anomalies projected against the correlation pattern between the second leading mode of July-September tropical Atlantic vertical wind shear and the January-March 200 hPa zonal wind field. The reanalysis dataset used is the ECMWF ERA-5 Reanalysis dataset. The wave breaking detection algorithm used to generate this index is outlined in Papin et al. (2020) and calculation of the AWB-associated shear is outlined in Jones et al. (2020). The data captures the main drivers (both tropical and subtropical) of summer tropical Atlantic vertical wind shear and is used in our study to quantify the added skill in extended-range statistical forecasts of tropical cyclone activity. For the original scripts that produced the archived indices, please contact the author at email@example.com or firstname.lastname@example.org.
Steps to reproduce
As outlined in Jones et al. (2020), the detection algorithm uses 6-hourly data from the ECMWF's ERA Reanalysis dataset (both ERA-Interim and ERA-5 have been used successfully). The algorithm uses 6-hourly zonal winds and 350-K potential vorticity (PV) data from 1979-2019. Vertical wind shear (VWS) is defined as the difference between 200 hPa and 850 hPa zonal wind fields. Detection and PV and VWS anomaly retrieval is restricted to the region 20-40N, 100-5W. Note that the resulting indices are sensitive to the domain chosen for detection. To generate the indices, the algorithm calculates the potential vorticity streamer intensity (PVSI) (Papin et al. 2020) from each PV streamer event detected. PVS intensity is defined as the standardized PV anomaly relative to a six-hourly climatological mean and is integrated over the areal extent of the PV streamer detected along the 2-PVU contour on the 350-K isentropic surface. The algorithm detects more than two consecutive points along the 2-PVU contour with an eastward (west to east) PV gradient and a reversal in the poleward meridional PV gradient for the upstream edge of the PV tongue. The opposite criteria is applied for detection of the downstream edge. Further details on the approach are outlined in Abatzolgou and Magnusdottir (2006), Jones et al. (2020) and Papin et al. (2020).