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The climatology and interannual variability of cyclone tracks in the National Center for Environmental Prediction's climate forecast system model for the Southern Hemisphere

Evaluating cyclone tracks in climate models represents an excellent way to evaluate their ability to simulate synoptic‐scale phenomena. Cyclone tracks were generated from two free‐runs from the National Centers for Environmental Prediction Climate Forecast System (CFSv1) model for the Southern Hemisphere (SH), and compared with cyclone tracks generated from CFS reanalysis and ERA Interim data from 1979 to 2016. It is demonstrated that CFSv1 is capable of simulating realistic SH cyclone track climatology for both intensity and frequency. The CFSv1's ability to capture interannual variability is also highlighted. Specifically, the impacts of the Antarctic Oscillation (AAO), El Niño/Southern Oscillation (ENSO), and the Indian Ocean Dipole (IOD) on cyclone track frequency and intensity were assessed. The CFSv1 exhibits an annular structure in frequency and intensity in response to the AAO. For the reanalysis data, AAO cyclone frequency is less annular in the South Pacific especially during Austral Summer, possibly due to a positive trend in the AAO in recent decades. To test this, a reconstruction of cyclone tracks for ERA40 data from 1958 to 2001 produces a more annular structure. The response of cyclone tracks due to ENSO is fairly robust, with the reanalysis datasets and one member of the CFSv1 producing a pattern of cyclone variability consistent with the Pacific South American teleconnection pattern. In contrast, the cyclone frequency and intensity response to the IOD shows little agreement between reanalysis and CFSv1. An examination of 200‐hPa stream function supports the CFS model producing a teleconnection response to ENSO but not the IOD, possibly due to anomalous heating generated from the IOD being too small. Our results suggest that assessing interannual variability of cyclone tracks in current state‐of‐the‐art models be done with large‐number ensembles when possible, especially when considering sensitivity to initial conditions and the magnitude of external forcing.