GPARM GFUNC and GVECT are the scalar and vector grid functions. They are input as nested strings of operators and operands. The operand list for an operator is enclosed in parentheses or square brackets, with operands separated by semicolons or commas. The following grids will be computed automatically from grids in the grid file, if possible: TMPK DWPK TVRK MIXR THTA DRCT TMWK TMPC DWPC TVRC SMXR STHA SPED TMWC TMPF DWPF TVRF MIXS THTE RELH TMWF THES SMXS STHE Mixing ratios will be computed automatically from dewpoint temperatures, specific humidity, or vapor pressure if a pressure grid exists. The stability indices will be computed automatically from temperature, dewpoint temperature, and wind speed and direction. These special scalar parameters are CTOT VTOT TOTL KINX SWET In addition, precipitation will be converted from inches (I) to millimeters (M) and vice versa, if the grids are named P__M or P__I. The middle characters are numbers giving the time interval over which the precipitation accumulated. For example, P24M is a 24-hour precipitation total. The units for sea surface temperature (SSTx), maximum temperature (TMXx), and minimum temperature (TMNx) will be converted automatically. ( x may be K, C, or F. ) These special scalar parameter names denote constant value grids: DTR Conversion factor for degrees to radians = PI / 180 E Base of natural logarithms = 2.71828182 GRAVTY Gravitational constant = 9.80616 (note spelling) KAPPA Gas constant/specific heat = 2/7 PI 3.14159265 RTD Conversion factor for radians to degrees = 180 / PI nnn Any number (e.g., 2, -10.2) Another class of special parameter names depends on the grid navigation: CORL Coriolis force = 2. * OMEGA * SIN ( LATR ) LATR Latitude in radians LONR Longitude in radians XVAL Value of the x coordinate in graph coordinates YVAL Value of the y coordinate in graph coordinates MSFX Map scale factor in the x direction MSFY Map scale factor in the y direction A grid may be identified by its number in the grid file by prefixing the number with the symbol #, e.g., #5. Standard vector grids are: WND Total wind GEO Geostrophic wind AGE Ageostrophic wind ISAL Isallobaric wind THRM Thermal wind Time, level, and vertical coordinate as specified through the user interface may be overridden by in-line parameters: ^time @level %ivcord appended to an operand in any combination. If more than one file is opened, +n may also be used as an in-line parameter, where "n" is the number corresponding to the position of the file list entered in GDFILE. If +n is omitted, the first file is used. For example, to advect temperature from file 3 using winds from file 1: GDFILE =file1.grd + file2.grd + file3.grd GFUNC =ADV ( TMPK+3, WND ) Grid operators may be nested. Note that layer and time range operators expect operands read directly from the grid file. GFUNC may include a name for the computed grid. This name may be used in later diagnostic functions in an application. The grid is stored in an internal, circular grid list and will eventually be overwritten. It will never be available after exiting the application. The name is specified after two slashes at the end of GFUNC. For example, GFUNC = DIV ( WND ) // DVRG permits the divergence to be used in a later calculation as DVRG, as in this example: GFUNC = LAP ( DVRG ) This name will also be the default name used in the title. In the following list of diagnostic operators, scalar operands are named Si, and vector operands are Vi. Vector components are denoted by u and v. All meteorological grids are in MKS units, except as noted. POL following the description indicates that the computation currently can only be performed on polar (R, THETA) grids. In the trigonometric functions, the angles are expressed in radians. The scalar constants used as arguments for the radial and tangential wind computations are defined as follows: LAT = latitude of storm center LON = longitude of storm center D = direction of storm motion ST = speed of storm motion The second input in each of the filter functions GWFS and GWFV is an integer N. N gives the wavelength in units of the grid spacing for which the theoretical response of a filter with normally distributed weights is 1/e = .3679. In practice, the actual response function will exceed the theoretical values at all wavelengths. The larger N is, the stronger the filtering will be. SCALAR OUTPUT GRID ABS (S) Absolute value ACOS (S) Arc cosine function ASIN (S) Arc sine function ATAN (S) Arc tangent function ATN2 (S1,S2) Arc tangent function COS (S) Cosine function EXP (S1,S2) Exponential to real EXPI (S1,S2) Exponential to integer [uses NINT(S2)] LN (S) Natural logarithm LOG (S) Base 10 logarithm SIN (S) Sine function SQRT (S) Square root TAN (S) Tangent function ADD (S1,S2) Addition MUL (S1,S2) Multiplication QUO (S1,S2) Division SUB (S1,S2) Subtraction ADV (S,V) Advection AVG (S1,S2) Average AVOR (V) Absolute vorticity BVSQ (THTA) Brunt-Vaisala frequency squared in a layer CROS (V1,V2) Vector cross product magnitude DDEN (PRES,TMPC) Density of dry air ( kg / m**3 ) DDR (S) Partial derivative with respect to R (POL) DDT (S) Time derivative DDX (S) Partial derivative with respect to X DDY (S) Partial derivative with respect to Y DEF (V) Total deformation DIRN (V) Direction relative to north DIRR (V) Direction relative to grid DIV (V) Divergence DOT (V1,V2) Vector dot product DTH (S) Partial deriv. with respect to THETA (POL) EPV (HGHT) Saturated equivalent geostrophic potential vorticity in a layer FCNT (S) Coriolis force at grid center (POL) FRNT (THTA,V) Frontogenesis GWFS (S,N) Filter with normal distribution of weights HIGH (S,RADIUS) Relative maxima over a grid (RADIUS is expressed in grid points) JCBN (S1,S2) Jacobian determinant KNTS (S) Convert meters / second to knots LAP (S) Laplacian operator LAV (S) Layer average (2 levels) LDF (S) Layer difference (2 levels) LOWS (S,RADIUS) Relative minima over a grid (RADIUS is expressed in grid points) MAG (V) Magnitude of a vector MASS Mass per unit volume in a layer from PRES MDIV (V) Layer-average mass divergence MIXR (DWPC,PRES) Mixing ratio g/g internally, g/kg on output MRAD (V,LAT,LON, D,ST) Magnitude of radial wind MSDV (S,V) Layer-avg. mass-scalar flux divergence MSFC (V) Psuedo angular momentum (for cross sections) MTNG (V,LAT,LON, D,ST) Magnitude of tangential wind NORM (V) Normal component (for cross sections) PLAT (S) Latitude at each point (POL) PLON (S) Longitude at each point (POL) POIS (S,S) Solve Poisson equation of forcing function with boundary conditions POLF (S) Coriolis force at each point (POL) PVOR (S,V) Potential vorticity in a layer RELH (TMPC,DWPT) Relative humidity RICH (V) Richardson stability number in a layer ROSS (V1,V2) Rossby number SAVG (S) Average over whole grid SAVS (S) Average over subset grid SDIV (S,V) Flux divergence of a scalar SHR (V) Shearing deformation SM5S (S) 5-point smoother SM9S (S) 9-point smoother STAB (TMPC) Lapse rate over a layer in K/km STR (V) Stretching deformation TANG (V) Tangential component (for cross sections) TAV (S) Time average TDF (S) Time difference THES (PRES,TMPC) Saturated equivalent potential temperature in Kelvin THTA (TMPC,PRES) Potential temperature THTE (PRES,TMPC, DWPC) Equivalent potential temperature TMST (THTE,PRES) Parcel temperature in Kelvin along a moist adiabat TMWK (PRES,TMPK, RMIX) Wet bulb temperature in Kelvin UN (V) North relative u component UR (V) Grid relative u component VN (V) North relative v component VOR (V) Vorticity VR (V) Grid relative v component WNDX (S1,S2,S3,S4) WINDEX (index for microburst potential) WSHR (V) Magnitude of the vertical wind shear in a layer XAV (S) Average along a grid row XSUM (S) Sum along a grid row YAV (S) Average along a grid column YSUM (S) Sum along a grid column VECTOR OUTPUT GRID AGE (S) Ageostrophic wind CIRC (V,S) Circulation (for cross section) DVDX (V) Partial x derivative of V DVDY (V) Partial y derivative of V GEO (S) Geostrophic wind GRAD (S) Gradient of a scalar GWFV (V,N) Filter with normal distribution of weights INAD (V1,V2) Inertial advective wind ISAL (S) Isallobaric wind KCRS (V) K cross V KNTV (V) Convert meters/second to knots LTRN (S,V) Layer-averaged transport of a scalar NORMV (V) Vector normal wind (for cross sections) QVEC (S,V) Q-vector at a level QVCL (S,V) Q-vector of a layer RAD (V,LAT,LON, D,ST) Radial wind ROT (angle,V) Coordinate rotation SMUL (S,V) Multiply a vector's components by a scalar SM5V (V) 5-point smoother SQUO (S,V) Vector division by a scalar TANGV (V) Vector tangential wind (for cross sections) THRM (S) Thermal wind over a layer TNG (V,LAT,LON, D,ST) Tangential wind VADD (V1,V2) Add the components of two vectors VASV (V1,V2) Vector component of V1 along V2 VAVG (V) Average vector over whole grid VAVS (V) Average vector over subset grid VECN (S1,S2) Create vector from north relative components VECR (S1,S2) Create vector from grid relative components VLAV (V) Layer average for a vector VLDF (V) Layer difference for a vector VMUL (V1,V2) Multiply the components of two vectors VQUO (V1,V2) Divide the components of two vectors VSUB (V1,V2) Subtract the components of two vectors