Surface met data file format

The files contain time series of surface meterological parameters (i.e. of air temperature, pressure and relative humidity, and of rainfall and downwelling shortwave radiation) recorded at 10 minute intervals at the NERC MST radar site.
Click here to find out about the contents of other files.

Data availability:
Data are available from 25th July 2000 to the present. There are a number of gaps in the dataset owing to instrument problems and down-time for maintenance. Refer to Instrument performance weblog.

File naming convention:
For data up to, and including, 12th April 2005:
sdYYMMDD.gz
For data after 12th April 2005:
met-sensors_capel-dewi_YYYYMMDD.na

	YYYY		is a 4-digit year [1990 - ]
	YY		is a 2-digit year [00 - 99]
	MM		is a 2-digit month [01 - 12]
	DD		is a 2-digit day [01 - 31]
	gz		indicates that the file is compressed with the GNU gzip algorithm
	na		indicates that the data are written in a NASA-Ames (ASCII) file format

Click here for the background to the file naming convention.

File location: /badc/mst/data/surface-met/
Click here for the location of other files.

Archiving convention:
For data up to, and including, 12th April 2005: YYYY
For data after 12th April 2005: YYYY/MM
Click here for a further explanation.

File formats
Click here for an overview of the different file formats used with the NERC MST Radar Facility dataset.

Data for dates up to, and including, 12th April 2005 are written in non-standard format ASCII files. Since the structure of these files is broadly similar to that used for data after 12th April 2005 (NASA-Ames files with a File Format Index of 1001), the earlier file format is described below with reference to the newer one. Eventually the data from the older files will be rewritten in the new format. For a complete description of the NASA-Ames file formats, consult the Gaines and Hipskind [1998] document. Only those aspects of the file which are essential for reading the data are described below.

The surface meteorological data file for 1st June 2005 will be used as an example. Text in green represents actual file contents. Text in red is for explanatory purposes only.

Header Lines

Line 1: 93 1001
Integer 1 corresponds to the total number of header lines, nr_header_lines
Integer 2 corresponds to the File Format Index

Line 7: 2005 06 01 2006 02 01
Integers 1 - 3 correspond to the year, month and day on which the observations were made.
Integers 4 - 6 correspond to the year, month and day on which the file was created.

Line 10: 10
The number of primary variables (nr_primary_vars).

Line 13: 999.99 999.99 999.99 9999.9 9.9999 999.9 9999.9 9.999 99.99 999.99
Missing data values, in order, for the nr_primary_vars primary variables - see below.

Lines 13 - 22
The names of the primary variables - see below

Line 27: 144
The number of data lines (nr_data_lines ) within the file.

Lines 28 - nr_header_lines:
These lines contain optional header information describing the instruments and the data product definitions. Some of this information is repeated below in association with the relevant data products but refer also to the surface meteorological instruments page.

Data reading loop
After reading the above mentioned lines, wind forward to line (nr_header_lines + 1) where the data begin. Since the number of header lines may change from file to file, it is important to read nr_header_lines from line 1 rather than assuming that it is always 93. The data can be read with a simple loop structure of the form (shown here in Fortran syntax):

do data_line_nr = 1,nr_data_lines
  read_data_line
end do

Reading the data line
The data lines contain 11 values: the first independent variable (time) followed by the 10 primary variables (all floating point numbers). The first 3 data lines from the file for 1st June 2005 are shown by way of example:

    0.0  11.41  11.41  11.89 9999.9 0.8310   0.0   -1.4 0.000 14.15  12.65
  600.0  11.23  11.23  11.34 9999.9 0.8470   0.0   -0.7 0.000 14.16  12.50
 1200.0  11.24  11.25  11.30 9999.9 0.8560   0.0   -0.3 0.000 14.16  12.42

Value 1: Seconds since 00:00:00 UTC (for the day in question) at the start of the 10 minute sample period (s)

Value 2: Minimum air temperature within the 10 minute sample period (°C)
The data logger initially samples the atmospheric temperature, pressure and humidity sensors at 5 s intervals. Mean values are calculated over each 60 s and the outputs from the logger represent minima, means and maxima of these 60 s means over each 10 minute sample period. Air temperature is measured with a Campbell Scientific 107 thermistor temperature probe mounted inside an URS1 unaspirated radiation shield. Accuracy: +/- 0.4 °C.

Value 3: Mean air temperature within the 10 minute sample period (°C)
Refer to explanation for value 2, above.

Value 4: Maximum air temperature within the 10 minute sample period (°C)
Refer to explanation for value 2, above.

Value 5: Mean air pressure within the 10 minute sample period (hPa)
Pressure is measured with a Vaisala PTB101B barometric pressure sensor. Accuracy: +/- 2.0 hPa. Refer also to explanation for value 2, above.

Value 6: Mean air relative humidity within the 10 minute sample period
Note that these values are in the range 0.000 - 1.000; they are not given as percentages. Humidity is measured by a Vaisala HMP45C temperature and relative humidity probe (from which only the humidity measurements are used) mounted inside an URS1 unaspirated radiation shield. Accuracy: +/- 0.3%. Refer also to explanation for value 2, above.

Value 7: Accumulated rainfall within the 10 minute sample period (mm)
The data logger initially samples the Environmental Measurements ARG100 tipping bucket raingauge every 1 s and records a tip for each 0.20 mm accumulation of rain. The output from the logger represents the total accumulation of rain over each 10 minute sample period. Note that occasional build-up of fungus within the inlet tube can impede or even completely inhibit the flow of rain into the instrument. This makes the rain data the least reliable of the surface meteorological measurements.

Value 8: Accumulated downwelling shortwave energy per unit area within the 10 minute sample period (kJ m-2)
The data logger initially samples the Kipp and Zonen CM3 thermopile pyranometer (WMO second class) every 5 s and records the downwelling radiation (within a hemispheric field of view) with a flat response in the spectral range 305 - 2800 nm. The output from the logger represents the accumulation of energy per unit area within each 10 minute sample period. Accuracy: +/- 0.5%.

Value 9: Estimated duration of sunshine within the 10 minute sample period (hours)
The measured radiation is compared with that predicted for the logger's latitude and longitude, and for the time of year and the time of day (assuming clear sky conditions). A sunshine priod is defined as one in which the ratio excedes 0.4 and the output from the logger represents the accumulated sunshine duration within each 10 minute sample period. Note that this is an estimated product, which is not derived according to the WMO definition of sunshine duration.

Value 10: Data logger battery voltage at the end of the 10 minute sample period (V)
The data logger records the instantaneous battery voltage and internal temperature at the end of each 10 minute sample period for performance checking purposes.

Value 11: Data logger internal temperature at the end of the 10 minute sample period (°C)
Refer to explanation for value 10, above.

Non-standard file format for dates up to, and including, 12th April 2005
The older files contain a subset of the information contained within the newer files. Refer to the product desriptions given above for the for the newer files. The files contain considerably less header information - confined to the first 3 lines. Note that the order of the data products differs to that used for the newer files. The first 6 lines of the file for 1st June 2003 (sd030601) are shown below in green.

 Surface data for Capel Dewi  Lat. 52.40  Long. -4.00
 Date 2003/06/01
 Time(Z) Temp.  Rad(KJ)   Hum(%)    mB   Rain(mm)
 00:10   12.99     -0.2    80.9    1004     0.0
 00:20   12.97     -0.2    80.9    1004     0.0
 00:30   12.92     -0.2    80.8    1004     0.0

Value 1: UTC Time (in hh:mm format) at the END of the the 10 minute sample period.
Note that the newer files relate the data the START of the 10 minute

Value 2: Mean air temperature within the 10 minute sample period (°C)

Value 3: Accumulated downwelling shortwave energy per unit area within the 10 minute sample period (kJ m-2)

Value 4: Mean air relative humidity within the 10 minute sample period
Note that these values are given as percentages rather than in the range 0.000 - 1.000.

Value 5: Mean air pressure within the 10 minute sample period (hPa)

Value 6: Accumulated rainfall within the 10 minute sample period (mm)

Internal Links:

Return to the top of the page

Access to the data

File naming convention

Surface meteorological instruments

External Links:

Location of surface meteorological data files on the BADC