THE NERC MST RADAR FACILITY AT ABERYSTWYTH
Click here to find out about earlier versions of the signal processing.
File contents
The files contain altitude profiles (from approximately 2 - 20 km for the ST mode, and from approximately 58 - 96 km for the M mode, both at 150 m intervals) of the eastward, northward and upward components of the wind velocity and the following radar return parameters: vertical beam signal power, aspect sensitivity, spectral width and beam-broadening corrected spectral width. The time separation between the profiles is typically a few minutes. A radar-derived tropopause altitude and sharpness is given for each set of profiles.
Click here to find out about the contents of other files.
File naming convention:
 |
YYYY | |
is a 4-digit year [1990 - ] |
| MM | is a 2-digit month [01 - 12] | ||
| DD | is a 2-digit day [01 - 31] | ||
| AA | is the altitude mode ['st': approximately 2 - 20 km | 'm': approximately 58 - 96 km] | ||
| RRR | is the range resolution (m) [150 | 300 | 600 | 1200 | 2400 | 4800] |
Click here for the background to the file naming convention.
File location: /badc/mst/data/mst-products-v2/cartesian/
Click here for the location of other files.
Archiving convention: YYYY/MM
Click here for a further explanation.
Data availability: refer to Instrument performance weblog
File format
NASA-Ames files, with a File Format Index of 2110, are used, i.e. the same as for Version-1 data products. However, there are some small differences in the file contents. Users will therefore need to make a few modifications to any software designed for dealing with Version-1 products.
Only those aspects of the file format which are essential for reading the data will be described. For a full description of the NASA-Ames formats, consult the Gaines and Hipskind [1998] document.
The Cartesian file for 1st January 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: 95 2110
Integer 1 corresponds to the total number of header lines, nr_header_lines
Integer 2 corresponds to the File Format Index
- Line 7: 2005 01 01 2005 01 10
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 11: 14
The number of primary variables (nr_primary_vars).
- Line 13: 9999.99 9999.99 99999 99 999.999 99999 999.99 99999 999.99 99999 99.999 99999 99.999 99999
Missing data values, in order, for the nr_primary_vars primary variables listed below. Greater use is made of missing data values than in the Version-1 files and so users should make sure that they make the appropriate substitutions when they read in the data.
- Lines 14 - 27
The names of the primary variables (listed below)
- Line 40: 130 366
Integer 1 corresponds to the number of altitude gates per cycle, nr_gates
Integer 2 corresponds to the number of cycles in the file, nr_cycles
- Lines 41 - 66:
Data product definitions - this information is shown, further down the page, in association with the relevant primary variables.
- Lines 67 - 93:
Global data attributes following the netCDF CF 1.0 convention. This includes a processing history. It is not necessary to know this information in order to read the file. - Line 7: 2005 01 01 2005 01 10
After reading the above mentioned lines, wind forward to line (nr_header_lines + 1) where the data begin. Associated with each cycle of observation there is a single line of auxiliary variables followed by nr_gates lines of primary variables. The data can therefore be read with a simple loop structure of the form (shown here in Fortran syntax):
do cycle_nr = 1,nr_cycles
read_auxiliary_variables
do gate_nr = 1,nr_gates
read_primary_variables
end do
end do
Reading auxiliary variablesEach auxiliary variables line contains 5 integers (the second independent variable followed by the 4 auxilliary variables) shown here for the first cycle in the file:
116 130 1 11086 3
- Integer 1: Cycle time (s)
Technically speaking this is the second independent variable rather than an auxiliary variable. The time is given in seconds since 00:00:00 UTC for the day in question.
- Integer 2: Number of range gates
This is the same as nr_gates given in line 40 of the header and so can be ignored.
- Integer 3: Cycle number
This is the same as cycle_nr used in the data reading loop and so can be ignored.
- Integer 4: Tropopause altitude (m)
This is the altitude of the (static stability) tropopause, in metres above mean sea level, determined from the altitude profile of the vertical beam signal strength.
- Integer 5: Tropopause sharpness factor
It should be noted that the altitude can have little significance for a poorly defined tropoapuse, i.e. for low values of the sharpness factor.0 corresponds to an indefinite tropopause 1 corresponds to lower-intermediate sharpness 2 corresponds to upper-intermediate sharpness 3 corresponds to a definite tropopause - Integer 2: Number of range gates
These lines contain 15 values: the first independent variable (altitude) followed by the 14 primary variables, as shown below for the first line of the first cycle. These are a mixture of floating point, F, and integer, I values.
1686.0 16.13 -3.36 32799 7 0.116 32771 57.82 32771 4.19 32771 0.309 32771 0.169 32771
- Value 1: Altitude (m) F
Technically speaking this is the first independent variable rather than a primary variable. Therefore it does not have a missing data value defined in line 13 of the header. Missing data values 1 - 14 therefore correspond to values 2 - 15 on the primary variable data line. The same altitude grid is used for all cycles and so only needs to be saved once. The altitude is given in metres above mean sea level.
- Value 2: Eastward wind (m s-1) F
or zonal velocity
- Value 3: Northward wind (m s-1) F
or meridional velocity
- Value 4: Horizontal wind reliability flag I
This applies to both the eastward and northward components of the wind. The way in which information is recorded in the reliability flag values is different to that used in Version-1 files. However, the same convention is used for all reliability flags in the Version-2 files - see below
- Value 5: Complementary beam horizontal velocity variability factor (m s-1) I
In the standard-mode, the MST radar makes observations in the Vertical, NE6, SE6, SW6 and NW6 beam directions. The NE component of the horizontal wind can therefore be derived from the Vertical/NE6 or Vertical/SW6 beam pair combinations. Similarly the SE component can be derived from the Vertical/SE6 or Vertical/NW6 combinations. The variability factor is defined as the root of the sum of the squares of the differences between the estimates in the NE and SE azimuths. A small value - less than 5 m/s - indicates that that the different wind estimates are consistent. Larger values - greater than 10 m/s - indicate that they are not and this fact is recorded in an enhanced data reliability flag.
- Value 6: Upward air velocity (m s-1) F
Note that this value can be biased for a number of reasons and should be interpreted as being representative rather than necessarily as quantitatively accurate. In particular, little significance should be attached to values of less than approximately 0.1 m/s. Absolute values of the order of 1 m/s give a reliable indication of the presence of mountain wave or convective activity.
- Value 7: Upward air velocity reliability flag I
See below
- Value 8: Radar return signal power (dB) F
Corresponds to obervations made with a vertically directed beam.
P_dB = 10 × log10[P_linear]
- Value 9: Radar return signal power reliability flag I
See below
- Value 10: Radar return aspect sensitivity (dB) F
The ratio of radar return signal power for a vertically directed beam to that for a beam directed 6° off-vertical.
- Value 11: Radar return aspect sensitivity reliability flag I
See below
- Value 12: Radar return spectral width (m s-1) F
This is for observations made by a vertically directed beam and corresponds to to an e-1/2 half-width for a Gaussian shaped signal. Note these values need to corrected for the effects of beam-broadening before they can be interpreted in terms of turbulent activity.
- Value 13: Radar return spectral width reliability flag I
See below
- Value 14: Beam-broadening corrected spectral width (m s-1) F
This is the highest order radar data product and is sensitive to errors and uncertainties in several lower order products. Care should therefore be taken with its interpretation. In principal it gives the standard deviation of turbulent velocities about the mean vertical velocity.
- Value 15: Beam-broadening corrected spectral width reliability flag I
See below
- Value 2: Eastward wind (m s-1) F
The same convention is used for all reliability flags in the Version-2 files, although this differs from that used for Version-1 files. A larger range of information is now stored bit-wise in a 16-bit integer, with the 15th bit being used as an overall indicator of data reliability. Therefore data may be regarded as reliable if:
The convention has been adopted so that more pieces of information can be added to the flag value at a later date, without changing the acceptance condition. At present, only 6 of the available 16 bits are used:
|
Bit number | |
Information |
| 0 | peak signal PSD to noise PSD >= threshold value | ||
| 1 | time continuity threshold exceded | ||
| 2 | complementary beams are available | ||
| 3 | complementary beam factor >= threshold value | ||
| 4 | complementary beam factor is significant | ||
| 15 | overall reliability flag |