helicopter CLASP data version 3

CLASP helicopter profile data: version 3

The matlab file contains a structure called CLASP_heli and met.
There were 39 flight profiles during the campagin with CLASP data availiable.

The met array contains:
ambient_pres : ambient pressure measurments from helicopter in 10m mean bins (Pa)
ambient_temp : same as pressure but for temp. (DegC)
ambeint_RH : same as pressure but for RH (%)
end_temp : temperature of the airmass at the entrance of the CLASP insturment after the amount of
warming has been estimate. (see below for more detail)
end_RH : RH at the entrance of the CLASP insturment using temp_end to relcalculate the RH.

The CLASP_heli array contains:
serial_time : date and time in matlab serial format
altitude : heights (meters) in 10m bins, each value is the bottom of
the bin.
date_vector : date and time in matlab vector format
DOY : day of year
mean_diameter : aerosol mean diameter per size bin
N : raw number concentrations in cc in mean 10m bins
dNdlogD : raw spectra, corrected for inlet losses.
dNdlogD_STP : same as dNdlogD but in standard temp and pressure
dNdlogD_NTP : same as dNdlogD but in normalised temp and pressure
dNdlogD_RHcor : dNdlogD spectra but also corrected to dry diameter using RH_end as RH of aerosol
when sampled.
mean_Dcor : the new mean diameters after the RH correction applied. N.B not now constant.
dNdlogD_RHcor_STP : same as dNdlogD_RHcor but in standard temp and pressure
dNdlogD_RHcor_NTP : same as dNdlogD_RHcor but in normalised temp and pressure

The CLASP aerosol spectra have been corrected for the loss of aerosol through the inlet tube
i.e. the straight line losses and the losses through the bends.

Being Version 3 a correction has now been made for RH. This is to correct for the amount of drying
that occurs through the 3m inlet tube inside the cabin. The drying is due to the high
temperature inside of the helicopter cabin compared to outside air mass. The temperature difference
causes a significant amount of drying; shifting the aerosol spectra and changing the shape and
magnitude of the measured aerosol spectra by the CLASP unit.

Using the temperature sensor in the CLASP unit which was exposed to the cabin airmass this
was averaged for each flight and was generally around 20 degC. The total flow rate was 8 litre/min.

The spectra was corrected using Feng and Shettle fomulation. This was done assuming the aerosols are
sea salt aerosols; NOTE this may not be the actual composition of the aerosol.

The first calculation estimates the temperature (end_temp) at the entrance to the CLASP unit and
thus the RH.We then use this RH (end_RH) to standardise all the spectra to dry radius (dNdlogD_RHcor).

contact: Sarah Norris (snorris@env.leeds.ac.uk)

heli_v3.zip2.02 MB