Tmean - vs - Z RxA+HARP

The temperature slopes for each month (per instrument) tend to have a negative trend with increasing temperature corresponding to decreasing Z. This is in agreement with the plots from 20090719 for the first 6 months of the year.

However this is not what the operators see night to night however. They report a typical trend of the highest Z at the start of the night, getting less positive as the night goes on (and the temperature drops).

Individual nights

Lets look at the Z focus offsets against temperature for 4 nights in July before the correction to DZT_COEFF was made.

And now after the correction...

Now see the same trend but with a steeper slope and a more positive offset.

This trend is in complete contrast to that seen when considering the combined data. Thus it appears that whilst the stating values for the night do follow a negative slope with increasing temperature corresponding to decreasing Z readings, the subsequent measurements follow a positive one with Z decreasing as T(mean) decreases.