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THE NERC MST RADAR FACILITY AT ABERYSTWYTH
Putting the M back into MST
Mesospheric-mode observations, covering the approximate altitude range 56 - 94 km, will be reintroduced from Wednesday 6th April 2005 - the first time since November 1999. This will not have a large impact on the ST-mode (2 - 20 km) observations, since only two extra dwells are being added to the current observation cycle. One will be a vertical beam dwell for the M-mode and the second will be a vertical beam dwell for the ST-mode. This will ensure that ST-mode vertical velocity profiles are still available at regular 46 s intervals (as they have been since June 2004). Users will need to access the radial data files in order to retrieve the high resolution information. The interval between horizontal velocity profiles (given in the Cartesian data files) will increase from 3 minutes 50 seconds to 4 minutes 36 seconds. Full details of these changes can be found below.
A warning for users of version-0 radial data products.
Version-2 signal processing automatically separates M and ST mode data into different files (as well as separating data by range resolution). However, version-0 radial data products are all written together in the same files. Depending on how they have written their reading routines, users may need to make slight changes if they want to ensure that only single mode data are considered. An indication that M-mode data are included for a particular dwell is given in line type 6 - see here for further details. It appears that only ST mode data are written in the version-0 wind files.
Users wishing to test their software are directed to the data for 12th June 1997, for which both M and ST mode observations are available. The situation for this date is a little different to that which is planned for the future - in that the M and ST mode observations are not interlaced within the same cycle - but this will give an indication of how the modes can be identified from the header lines.
Further details about the new observation format
The ST mode observation format used from 21st June 2004 - 5th April 2005 is as follows:
Dwell number : 1 2 3 4 5 6 7 8 9 10 Beam direction : NE6 Vert SW6 Vert SE6 Vert NW6 Vert W4.2 Vert Range Resolution: 300 300 300 300 300 300 300 300 300 300 Mode : ST ST ST ST ST ST ST ST ST STEach dwell has a duration of approximately 23 s and so the total cycle time is 3 minutes 50 seconds. Although only one horizontal wind profile is available per cycle, vertical velocity profiles are available every other dwell, i.e. at intervals of 46 s, from the radial data files. The new format, to be introduced on 6th April 2005, is identical except that it has two extra dwells per cycle:
Dwell number : 1 2 3 4 5 6 7 8 9 10 11 12 Beam direction : NE6 Vert SW6 Vert SE6 Vert NW6 Vert W4.2 Vert Vert Vert Range Resolution: 300 300 300 300 300 300 300 300 300 300 1200 300 Mode : ST ST ST ST ST ST ST ST ST ST M STNote (added 11th April 2005): Owing to technical problems encountered when trying to observe the mesosphere at 1200 m range resolution, observations are now being made at 300 m resolution instead.
Since the duration of the M mode dwell is identical to that of ST mode dwells (23 s), vertical velocity profiles will still be available at regular 46 s intervals. The separation between horizontal wind profiles will increase slightly to 4 minutes 36 seconds.
Why bother making M mode observations at all?
Clearly with only vertical beam observations available for the M mode, it will not be possible to derive horizontal winds. Nevertheless the new observations will be invaluable for establishing when, and from which altitudes, mesospheric radar returns are observed. As can be seen from the quick-look plot for the 12th June 1997 case, referred to above, detectable radar returns are from discrete layers of narrow vertical extent. Moreover, they tend to occur only sporadically. However, M mode observations have never been made in a systematic way with the Aberystwyth radar. Although observations lasting several hours (albeit on arbitrary days) were made in the early 1990s, as can also be seen from the quick-look plot for the 12th June 1997 case, much shorter (and less frequent) observations were made thereafter.
Attention tended to be focused on the unusually strong and persistent echoes observed around 85 km during June and July (as seen for the 12th June 1997 case). These are analogous to the Polar Mesosphere Summer Echoes (PMSEs), observed at higher latitudes, which are known to be associated with the extra-ordinarily low temperature of the summer mesopause level. The low temperature is also responsible for the occurrence of noctilucent clouds (NLC), which can sometimes be seen from Aberystwyth during mid-summer nights. If you would like more details about mesospheric radar observations, please contact the NERC MST Radar Facility Project Scientist or refer to the early papers making use of data from the radar.
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Last updated 11th April 2005