Global forecasts of thermospheric gravity wave activity as generated from tropospheric sources: An overview of the foregrats model with application to the prediction of equatorial spread-F

Atmospheric gravity waves, generated primarily from tropospheric mesoscale convective complexes and frontal systems, propagate into the middle atmosphere and subsequently impact the entire global circulation. Furthermore, the short-period/long vertical wavelength portion of the gravity wave spectrum can propagate into the thermosphere, where such waves can potentially "seed" equatorial spread-F (ESF), an instability phenomena which causes scintillation in the radio portion of the electromagnetic spectrum. Recently, the desire to acquire 4-6 hour forecasts of ESF has come to the forefront of upper atmospheric research because of the impacts on radio communications and GPS signals. However, to extend these forecasts beyond the 6 hour limit, the modeling of the synoptic gravity waves associated with ESF needs to be addressed. As such, in this paper we present a global gravity wave forecasting model called FOREGRATS (FOREcasting of Gravity waves via Ray-tracing algorithms with prescribed Tropospheric Sources), which uses a myriad of data resources to identify dominant tropospheric gravity wave sources, prescribe a relevant source spectrum, and then propagate the resultant gravity waves through the middle and upper atmosphere via a linear ray-tracing theory. An example of the entire data assimilation and forecasting processes is presented, outlining each of the major components of the model.