calc_gradient_speed: Convert symmetric surface wind to gradient wind.

Description Usage Arguments Details Value References

View source: R/wind_conversions.R


Converts maximum 10-m 1-minute symmetric sustained wind speed to gradient wind speed. The conversion factor depends on whether the storm is over land or water.


calc_gradient_speed(vmax_sfc_sym, over_land)



A numeric vector of 1-minute sustained wind speed at 10 meters, with motion asymmetry removed (m / s).


TRUE / FALSE of whether the storm is over land (TRUE) or water (FALSE).


This function uses the following conversion:

Vmax,G = Vmax,sym / fr


The function uses a reduction factor based on Figure 3 in Knaff et al., 2011. If over water and within 100 kilometers of the storm's center, the ratio of gradient wind speed to surface wind speed is assumed to be 0.90. If over land, this reduction factor is reduced by 20% (0.9 * 0.8 = 0.72).

For this calculation, we assume that the radius of maximum wind for all storms is 100 kilometers or smaller (in the code, we do not calculate R_max until after we estimate gradient wind speed from surface wind speed, so we don't have that storm-specific estimate to use here).


A numeric vector with maximum gradient-level 1-min wind speed (m / s).


Knaff JA, DeMaria M, Molenar DA, Sampson CR, and Seybold MG. 2011. An automated, objective, multiple-satellite-platform tropical cyclone surface wind speed analysis. Journal of Applied Meteorology and Climatology 50(10):2149-2166

geanders/stormwindmodel documentation built on Oct. 15, 2018, 12:06 p.m.