Unified West-Coast and Gulf-Coast AR Indices to Study the Hydrological and Cloud-Radiative Effects of the Atmospheric Rivers over the Contiguous US

Atmospheric rivers (ARs), the long, narrow filaments of enhanced water vapor transport in the lower troposphere, have significant hydrological impacts on the western North America and the central United States. We are undertaking an observational climatology study of ARs that either reached the western coast (the West-Coast ARs) or intruded into the Gulf of Mexico (the Gulf-Coast ARs) from the cloud-radiative effects perspective. The differences between the ARs’ hydrological properties and the related aerosol and cloud-radiation processes are examined using data from the ERA-interim reanalysis, Global Precipitation Climatology Project (GPCP), A-Train CALIPSO, and the Clouds and the Earth’s Radiant Energy System (CERES) products. The linkage between the West-Coast ARs and the Gulf-Coast ARs are under study, so are their collective cloud-radiative effects over the contiguous US (CONUS).

The first and critical analysis task was to develop a consistent algorithm for automatic detection of both West-Coast ARs and Gulf-Coast ARs. Three AR detection algorithms, respectively, based on the column-integrated water vapor transport (IVT), the column-integrated water vapor (IWV), as well as the combined IWV and IVT were examined and applied to both the West-Coast ARs and the Gulf-Coast ARs during the period Nov-Mar, 2006-2014. Sixty-two (62) cases of West-Coast ARs are detected based on the IVT, compared with 64 based on the IWV and 32 based on the combined IWV and IVT algorithms. For the Gulf-Coast ARs, the detected cases are 61, 78, and 52, respectively. The average total rainfall, therefore the regional hydrological impact, associated with the two types of ARs under the three detection algorithms are analyzed and visualized using the quantile-quantile (Q-Q) plots. The results show that both the West-Coast ARs and the Gulf-Coast ARs detected by the IVT-based algorithm are associated with more average total rainfall in the two regions than the other two detection methods. The IWV-based AR index is associated with the least amount of rainfall. The combined IVT and IWV algorithm is only a compromise between the two sole variable algorithms. This result is different from a previous study that preferred the combined IWV and IVT detection algorithm for both types of ARs. The IVT-based AR indices are therefore used for further and ongoing analysis of the aerosol contents and cloud-radiative effects of the two types of ARs individually and collectively over the CONUS with CALIPSO and CERES data. Results will be detailed at the talk.