dX: Derivatives

In metno/esd: Climate analysis and empirical-statistical downscaling (ESD) package for monthly and daily data

Derivatives

Description

dX, dY, and dT are functions to estimate derivatives for gridded field objects based on a fit to truncated Fourier series. The three functions give the x-, y- and time derivatives respectively. See Benestad & Chen (2006) 'The use of a Calculus-based Cyclone Identification method for generating storm statistics' (Tellus A 58A, 473-486, doi:10.1111/j.1600-0870.2006.00191) for more details.

Usage

dX(
  Z,
  m = 10,
  mask.bad = TRUE,
  plot = FALSE,
  r = 6378000,
  accuracy = NULL,
  progress = TRUE,
  verbose = FALSE
)

Arguments

Z	A field object
m	number of harmonics for fitting the Fourier series
mask.bad	mask missing data
plot	if TRUE show plot
r	radius of the Earth (m)
accuracy	resolution of output
progress	show the progress
verbose	show diagnostics of the progress

Details

regfit is a help function for generating a model for fitting the profile.

Value

a list with several components:

Z	original data
a	Fourier coefficients for cosine
b	Fourier coeffieicnes for sine
z0	defunct?
dZ	The component contains the first derivative.
dZ2	The component contains the second derivative (quicker to do both in one go).
lon	longitude
lat	latitude
dx	spatial resolution
span	spatial extent

Examples

data(slp.ERA5)
slp.dx <- dX(slp.ERA5,verbose=TRUE)
map(slp.dx$Z) # map of SLP 
map(slp.dx$dZ) # map of first derivative in longitude direction
map(slp.dx$dZ2) # map of second derivative in longitude direction
## Not run: 
u10 <- retrieve('~/Downloads/Jan2018_ERAINT_uvp.nc',param='u10')
v10 <- retrieve('~/Downloads/Jan2018_ERAINT_uvp.nc',param='v10')
## Estimate the vorticity
zeta <- dX(v10)$dZ - dY(u10)$dZ
zeta <- attrcp(u10,zeta)
class(zeta) <- class(u10)
attr(zeta,'variable') <- 'vorticity'
attr(zeta,'unit') <- '1/s'
map(subset(zeta,it=1),projection='np')

## End(Not run)

metno/esd documentation built on Feb. 25, 2025, 6:44 p.m.