Read an ocean index file, in the format used by NOAA.

read.index(
file,
format,
missingValue,
tz = getOption("oceTz"),
debug = getOption("oceDebug")
)

## Arguments

file a connection or a character string giving the name of the file to load. May be a URL. optional character string indicating the format type. If not supplied, a guess will be made, based on examination of the first few lines of the file. If supplied, the possibilities are "noaa" and "ucar". See “Details”. If supplied, this is a numerical value that indicates invalid data. In some datasets, this is -99.9, but other values may be used. If missingValue is not supplied, any data that have value equal to or less than -99 are considered invalid. Set missingValue to TRUE to turn of the processing of missing values. character string indicating time zone to be assumed in the data. a flag that turns on debugging, ignored in the present version of the function.

## Value

A data frame containing t, a POSIX time, and index, the numerical index. The times are set to the 15th day of each month, which is a guess that may need to be changed if so indicated by documentation (yet to be located).

## Details

Reads a text-format index file, in either of two formats. If format is missing, then the first line of the file is examined. If that line contains 2 (whitespace-separated) tokens, then "noaa" format is assumed. If it contains 13 tokens, then "ucar" format is assumed. Otherwise, an error is reported.

In the "noaa" format, the two tokens on the first line are taken to be the start year and the end year, respectively. The second line must contain a single token, the missing value. All further lines must contain 12 tokens, for the values in January, February, etc.

In the "ucar" format, all data lines must contain the 13 tokens, the first of which is the year, with the following 12 being the values for January, February, etc.

## References

See https://www.esrl.noaa.gov/psd/data/climateindices/list/ for a list of indices.

## Examples


if (FALSE) {
library(oce)
par(mfrow=c(2, 1))
# 1. AO, Arctic oscillation
oce.plot.ts(aorecent$t, aorecent$index)
oce.plot.ts(soirecent$t, soirecent$index)
}