radvert −− compute vertical velocity, divergence, and hydrometeor terminal velocity for common data format radar data file
radvert [-w wtval] u v w d wi wt [dbz wcp]
Radvert expects a three−dimensional, synthesized common data format radar data file, such as might be produced by radcedric, on the standard input. This file is transferred to the standard output with the addition of certain fields. The added fields are the horizontal divergence, the continuity−generated vertical velocity, the hydrometeor terminal velocity and various ambient profiles. Normally the terminal velocity is computed as the difference between the continuity−generated vertical velocity and the vertical particle velocity. However, inclusion of the optional arguments causes the terminal velocity to be computed from an assumed terminal velocity−reflectivity relationship. In this case a vertical air velocity based on the vertical particle velocity and the above terminal velocity is also computed. This is called the cloud physics vertical velocity. The above fields are added to the variable slice section, whereas the ambient density, pressure, and scale height profiles are added to the static slice. Though normally only one variable slice occurs per file, radvert will treat an arbitrary number.
The meanings of the command line arguments are as follows. u, v, and w are the names of x, y, and z components of the hydrometeor velocity, as synthesized by NCAR’s Cedric program. These must be on the input file, except possibly for w, as discussed below. D is the desired name for the horizontal divergence, and is calculated by radvert from u and v. Wi is the desired name for the integrated vertical velocity and is calculated by radvert from d and optionally w. Wt is simply w − wi, and is calculated by radvert.
Normally d is calculated using centered differences on u and v. However, if missing data would prevent the centered difference calculation of d at some point, off−centered differences are tried.
Wi is calculated by integrating the continuity equation down from cloud top. A density scale height based on a constant lapse rate model is used, with assumed temperature = 300 K at sea level and lapse rate of 7 K/km. The density, pressure, and scale height fields used are included in the output static slice. If they exist in the input file, they are re−calculated.
Normally, wi is initialized at cloud top as w + wtcldtop, where wtcldtop = 2 m/s is the assumed hydrometeor terminal velocity at the radar−sensed cloud top. If the w field is missing, wi is initialized to zero at cloud top. wt is not computed if w is missing. With the optional -w flag, wtcldtop is set to wtval rather than 2 m/s. With the optional -v flag wtcldtop = 4*divtop/divmax + 1 m/s, where divtop is the divergence at cloud top and divmax = 5/dz, dz being the vertical grid interval. Wtcldtop is not allowed to exceed the range [1, 5 m/s]. If wi is initialized from w, the divergence must also exist at that point or just below. This eliminates some spurious data.
Optional command line arguments are the reflectivity field (in dbz), which must already exist, and the requested name of the new cloud physics vertical velocity field. The assumed terminal velocity−reflectivity relationship is strictly empirical, and is given by wt = −exp(dbz/31.8 + 0.918). (Note that terminal velocities are defined to be negative.) In this mode the divergence field is converted in to the residual of the mass continuity equation using the cloud physics vertical velocity. This allows a check on how well (u, v, wcp) satisfy continuity.
Units of velocity are m/s, while distance is measured in km. Density is measured in kg/m^3, while pressure is measured in kpa. If any of the output fields already exist in the input file, the corresponding calculation isn’t done, and the input field isn’t overwritten.
kestrel%radvert u v w div winteg wterm zcp4 wcp < cooked > burnt
The common data format file "cooked" is read. It is assumed to contain particle velocity component fields u, v, and w. It creates the divergence (div), continuity−generated vertical velocity (winteg), and the hydrometeor terminal velocity (wterm) fields. These fields are added to the common data format file and written to "burnt". The density, pressure, and scale height fields are also added. Since the optional reflectivity and cloud physics vertical velocity fields are also specified, the latter is created, and wterm is overwritten with the cloud physics version.
kestrel%radvert u v ’*’ div winteg wterm < cooked > burnt
In this case the vertical particle velocity doesn’t exist. It’s space is held by the asterisk, which must be quoted for protection from the shell. Zero velocity initilization is used on winteg, and wterm is not created or added to "burnt". However, the wterm argument must still be present on the command line.
Radvert doesn’t do extensive checking on the size and dimensions of input fields. If these take on unexpected values, trouble could result.
Bugs occasionally act like hydrometeors.