Calculate geostrophic winds

Geostrophic wind from a geopotential height field.

GeostrophicWind(gh, lon, lat, cyclical = "guess", g = 9.81, a = 6371000)

Arguments

gh

geopotential height

lon

longitude in degrees

lat

latitude in degrees

cyclical

boundary condition for longitude (see details)

g

acceleration of gravity

a

Earth's radius

Value

A named list with vectors for the zonal and meridional component of geostrophic wind.

Details

If cyclical = "guess" (the default) the function will try to guess if lon covers the whole globe and set cyclical conditions accordingly. For more predictable results, set the boundary condition explicitly.

See also

Other meteorology functions: Derivate(), EOF(), WaveFlux(), thermodynamics, waves

Examples

data(geopotential)
geopotential <- data.table::copy(geopotential)
geopotential[date == date[1], c("u", "v") := GeostrophicWind(gh, lon, lat)]
#> Index: <date>
#>           lon   lat   lev       gh       date     u           v
#>         <num> <num> <int>    <num>     <Date> <num>       <num>
#>      1:   0.0 -22.5   700 3163.839 1990-01-01    NA  1.08181190
#>      2:   2.5 -22.5   700 3162.516 1990-01-01    NA  0.55189199
#>      3:   5.0 -22.5   700 3162.226 1990-01-01    NA  0.06625043
#>      4:   7.5 -22.5   700 3162.323 1990-01-01    NA -0.29800162
#>      5:  10.0 -22.5   700 3163.097 1990-01-01    NA -0.75064329
#>     ---                                                        
#> 290300: 347.5 -90.0   700 2671.484 1995-12-01    NA          NA
#> 290301: 350.0 -90.0   700 2671.484 1995-12-01    NA          NA
#> 290302: 352.5 -90.0   700 2671.484 1995-12-01    NA          NA
#> 290303: 355.0 -90.0   700 2671.484 1995-12-01    NA          NA
#> 290304: 357.5 -90.0   700 2671.484 1995-12-01    NA          NA
library(ggplot2)
ggplot(geopotential[date == date[1]], aes(lon, lat)) +
    geom_contour(aes(z = gh)) +
    geom_vector(aes(dx = u, dy = v), skip = 2) +
    scale_mag()