Global Three-Dimensional Water Vapor Feature-Tracking for Horizontal Winds From Overlapped Tracks of Two Satellites (NOAA-20 and Suomi-NPP)

The three-dimensional (3D) structure of the global horizontal wind field remains largely unobserved. Atmospheric Motion Vectors (AMVs) based on cloud tracking have been used since the 1960s to fill some of the gaps in global wind fields observation. However, all these cloud-tracking AMVs face a fundamental problem: each AMV is assigned to only a single level of cloud top at a given horizontal coordinate and therefore dense vertical profiles are not retrieved. This limits the study of very important phenomena where the vertical dimension is crucial, like organized convection.

More recent advances in remotely sensed, hyperspectral retrieval of water vapor have made the retrieval of a dense vertical profile of winds, that is 3D AMVs, possible. Here we develop an algorithm to retrieve winds for 9 pressure levels at 1◦ grid spacing from 60◦N to 60◦S. The retrieval is done by tracking water vapor from the hyper-spectral Cross-track Infrared Sounder aboard two polar satellites (NOAA-20 and Suomi-NPP) that have overlapped tracks separated by 50 minutes. We use a water vapor product from the Community Long-term Infrared Microwave Combined Atmospheric Product System (CLIMCAPS) which has 1◦ horizontal grid spacing for the overlapped tracks. The retrieval is done without prescribing a first guess; instead, we impose a gross error check by flagging retrievals that are too different from ERA-5 reanalysis. Testing the algorithm for the first week of January and July 2020 indicates that our algorithm yields 10^4 wind profiles per day and these 3D winds qualitatively agree with ERA-5. Compared with radiosonde data, the errors are within the range of reported errors of cloud-tracking winds.

The 1◦ grid spacing is too coarse to study phenomena at the mesoscale level, where observations could help fill gaps in knowledge about organized convection. However, recently, the development of a higher horizontal resolution hyperspectral water vapor product, the Single Field-of-view Sounder Atmospheric Product (SiFSAP), with a horizontal resolution of 14 km, has made the retrieval of mesoscale 3D AMVs possible. We are currently retrieving the higher resolution 0.25 deg x 0.25 deg 3D winds, and evaluating the performance of the retrievals at 0.25 deg versus 1 deg. These results will be discussed in our presentation.

The relevance to aviation meteorology of our efforts in the satellite retrieval of 3D winds will be discussed briefly.