# NCEP.FlowSpeed: Calculate flow-assistance according to equation 'FlowSpeed' In RNCEP: Obtain, Organize, and Visualize NCEP Weather Data

## Description

This function calculates flow-assistance according to equation FlowSpeed and determines the speed of forward and sideways movement if an animal behaves according to the rules of equation FlowSpeed.

## Usage

 `1` ```NCEP.FlowSpeed(u, v, direction, airspeed,...) ```

## Arguments

 `u` A numeric value indicating the U (i.e. zonal or east/west) flow component in meters per second, toward east being positive. Values must describe the direction into which the flow is moving. `v` A numeric value indicating the V (i.e. meridional or north/south) flow component in meters per second, toward north being positive. Values must describe the direction into which the flow is moving. `direction` A numeric value indicating the preferred direction of movement in degrees from North. For this function, `direction` is required but does not change the calculation of flow-assistance or the direction of movement. The argument is included for use with `NCEP.flight`. `airspeed` The airspeed of the animal in meters per second. This value does not affect the calculation of flow-assistance, but does affect the forward and sideways movement of the animal. `...` Any extra arguments passed to the flow-assistance equation.

## Details

This function calculates flow-assistance and forward and sideways movement according to equation FlowSpeed. Equation FlowSpeed assigns the speed of the flow (e.g. wind speed) as flow-assistance, therefore it can never produce negative flow-assistance values. It assumes that the animal applies its own airspeed in the same direction as the flow (e.g. wind direction).

## Value

A `data.frame` containing flow-assistance (‘fa’), the animal's forward speed (‘forward.move’ which includes the animal's own airspeed), the animal's sideways speed (‘side.move’ which includes the animal's own airspeed), the component of the flow parallel to preferred direction of movement(‘tailwind’), the component of the flow perpendicular to the preferred direction of movement (‘sidewind’), the animal's speed relative to the flow (‘airspeed’), and the animal's speed relative to the fixed Earth (‘groundspeed’) each in meters per second, presuming `u`, `v`, and `airspeed` were given in meters per second.

## Author(s)

Michael U. Kemp [email protected]

## References

To cite package 'RNCEP' in publications use:

Kemp, M. U., van Loon, E. E., Shamoun-Baranes, J., and Bouten, W. 2011. RNCEP:global weather and climate data at your fingertips. – Methods in Ecology and Evolution. DOI:10.1111/j.2041-210X.2011.00138.x.

 ```1 2 3``` ```library(RNCEP) ## Using NCEP.FlowSpeed to calculate flow-assistance ## tst <- NCEP.FlowSpeed(u=-2, v=-1, direction=225, airspeed=12) ```