Kain-Fritsch Convective Parameterization Trigger Function variables derived using ARM Ground- and VIIRS Satellite-based Observations

A convective parameterization scheme (CPS) that is used in numerical weather prediction (NWP) models account for subgrid scale vertical transports of energy and mass, reduces thermodynamic instability and redistributes temperature and moisture in a model grid cell. These parameterizations are often used in coarser resolution (4 km or higher) NWP simulations to resolve deep convection. Most CPSs have a trigger function, which is used to determine if conditions are met for the possibility of deep convection to occur in a model grid cell. One of the most well-known CPSs is the Kain-Fritsch (KF). This CPS is a mass flux scheme in which ensembles of clouds will have a cumulative effect on the environment. In addition, these schemes implicitly calculate updrafts/downdrafts and entrainment/detrainment. Deriving trigger function variables over spatial domains would not only provide insights into the occurrence of deep convection, while also comparing a region to NWP model simulations using the KF CPS could lead to improved predictions of the trigger function parameters, which would improve forecast accuracy.

The trigger function in the KF has two crucial variables: cloud base height (CBH) and cloud base vertical velocity (CBVV). In this study, Visible Infrared Imaging Radiometer Suite (VIIRS) satellite data coupled with ground instruments (Doppler Lidar [DL], radiosonde, and surface meteorological stations) from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site allows for a unique and novel proof-of-concept approach for retrieving both CBH and CBVV across a domain that spans approximately 2° x 2° longitude and latitude surrounding the SGP ARM site. The algorithm methodology involved splitting the larger domain for the retrieval of CBH and CBVV into sub-regions and removes VIIRS pixels that are not associated with both mature clouds and ground commination. The CBH retrieval uses a combination of the VIIRS satellite and the ground products derived across the SGP domain, along with results from Zheng et al (2015), to subsequently calculate CBVV. Ground observations from the DL are compared to the VIIRS satellite retrieved CBH and CBVV.

Results will be shown for over 80 case days from 2018-2021 May-August that exhibit shallow cumulus, which have the potential to develop into deeper cumulus clouds. Initial results are promising with moderate (~0.70) correlations of CBH to the DL observed CBH over the 80 case dates. With the prospects of CONUS-wide GeoXo high-resolution visible and infrared satellite data coverage similar to VIIRS comes the ability to capture the short-term (5-15 min) temporal evolution of convective clouds, which makes the results of this study applicable to regional operational NWP.