Radx2Grid Convective Stratiform

Overview

One important functionality of Radx2Grid is the ability to distinguish between convective stratiform and separation precipitation in gridded radar data. The algorithm is a modified version of the process described by Steiner et al. (1995), which analyzes the radar reflectivity field and flags grid points as convective or stratiform precipitation. Distinguishing between the two precipitation types is important due to the distinct profiles of vertical velocity, microphysical processes, and diabatic heating in convective and stratiform precipitation. This page will describe the basic methodology and point the user to key parameters.

Separation Process

The default setting of Radx2Grid is to not perform the convective stratiform separation and must be enabled in the parameter file (identify_convective_stratiform_split; line 2428).

As in Steiner et al. (1995), the first step is to identify definite convection. This process is done by flagging all points that exceed a user-defined reflectivity threshold as convective (conv_strat_dbz_threshold_for_definite_convection; line 2491). Note that this threshold will vary in continental and tropical convection (e.g., 53 vs 40/45 dBZ). Around each point flagged as definite convection, all points within a radius of convective influence are also flagged as convection (conv_strat_convective_radius_km; line 2504).

While Steiner et al. (1995) then calculates the reflectivity difference between a point and its neighbors to identify any remaining convection, Radx2Grid instead analyzes the "texture" of the reflectivity field, which is defined as [math]\displaystyle{ \sqrt{\sigma(dBZ^2)} }[/math]. The texture is calculated over all points within a user-defined radius of the central point (conv_strat_texture_radius_km; line 2519) and is only valid if the fraction of points within the texture radius exceeds a minimum fraction (conv_strat_min_valid_fraction_for_texture; line 2533). All locations where the texture exceeds a user-defined threshold are also defined as convection (conv_strat_min_texture_for_convection; line 2547). Similar to the first step, all points within the radius of convective influence are also flagged as convection.

Additionally, while Steiner et al. (1995) performs the aforementioned analysis at a single horizontal level, Radx2Grid will perform the analysis over a vertical layer of a user-defined depth (conv_strat_min_valid_height and con_strat_max_valid_height; lines 2452, 2464).

Note: the algorithm is currently undergoing significant upgrades that will be included in a future version of LROSE, possibly in a standalone application instead of within Radx2Grid.

Example

An example from Taiwan is shown below.

References

Steiner, M., Houze , R. A., Jr., & Yuter, S. E. (1995). Climatological Characterization of Three-Dimensional Storm Structure from Operational Radar and Rain Gauge Data, Journal of Applied Meteorology and Climatology, 34(9), 1978-2007. Link