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I am using RNOAA R package isd to download NOAA integrated surface data for a meteorological station (2016 data for Heathrow in London) for the purpose of air quality dispersion modelling. The modelling requires hourly wind speed, wind direction, humidity temperature, precipitation and cloud cover.

Wind speed, wind direction, humidity and temperature seem to be straightforward and can just be extracted for use. The problems are with cloud cover and precipitation.

For the cloud cover, the column "GA1_coverage_code" gives a range of values from 1 to 8 and then 99 and N/A. I gather the N/A means data are not available and 99 means missing data. I contemplate there should be 0 in the column. The other column "GF1_coverage" only gives 0, 9, 99 and N/A. I am wondering whether combination of the two columns should give a complete cloud cover dataset. However, i am not sure. anyone could throw some light on this?

For the precipitation, the dataset column "AA1_depth" gives precipitation readings for every 6 hours, 0, 6, 12, 18. my understanding is that at 0 and 12, the data give 6h cumulative precipitation for the previous 6 hours and at 6 and 18 the data give 12h cumulative precipitation for the previous 12 hours. I think I can write a code to interpolate the 6h resolution into hourly data. However, is there any code available for use?

You help would be greatly appreciated.

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