calc_helicity {meteoEVT}

Helicity density

Description

Calculates the helicity density (scalar product of wind vector and vorticity vector) either for the whole vector (3d) or only for the vertical component (updraft helicity)

Usage

calc_helicity(
  u_fld,
  v_fld,
  w_fld,
  lev_p,
  lat = NULL,
  dx = 0.25,
  dy = 0.25,
  vert_only = FALSE,
  relative = TRUE,
  zvort_fld = NULL,
  mode = "lonlat"
)

Arguments

u_fld

zonal velocity field [m/s]

v_fld

meridional velocity field [m/s]

w_fld

vertical velocity field [m/s]

lev_p

vector containing pressure levels [Pa]

lat

vector containing latitude

dx

x resolution in the corresponding unit (e.g. 0.25 degree for ERA5 with mode='lonlat' or e.g. 1000 m in cartesian coordinates with mode='cartesian')

dy

y resolution in the corresponding unit (e.g. 0.25 degree for ERA5 with mode='lonlat' or e.g. 1000 m in cartesian coordinates with mode='cartesian')

vert_only

logical, TRUE: if only the updraft helicity w*zeta (based on z-vorticity) should be calculated, FALSE: for 3d helicity (based on 3d vorticity), default: FALSE

relative

logical, TRUE: only relative vorticity, FALSE: whole (absolute) vorticity should be used for calculation of enstrophy, default: TRUE

zvort_fld

optional zvort field (if e.g., zvort is directly taken from ERA5 and not calculated separately)

mode

use 'lonlat' if the data is given on a lon-lat-grid or 'cartesian' if the data is given on an equidistant cartesian grid

Value

helicity density field [m/s^2]

Examples

myfile=system.file("extdata", "era5_storm-zeynep.nc", package = "meteoEVT")
data = readin_era5(myfile)
#3d helicity
hel=calc_helicity(data$u,data$v,data$w,data$lev,lat=data$lat)
#updraft helicity
up_hel=calc_helicity(data$u,data$v,data$w,data$lev,lat=data$lat,vert_only=TRUE)