SNAPSHOT OF WIND PROFILER MEASUREMENTS DURING CSIP AND COPS.

Abstract

The FGAM (Facility for Ground based Atmospheric Measurements) wind profiler is a 1290 Mhz ‘clear’ air weather radar manufactured by Degreane Horizon. It is a mobile instrument and has been regularly deployed as part of many field campaigns, including CSIP (Convective Storm Initiation Project) and COPS (Convective and Orographically-induced Precipitation Study). During CSIP and COPS the wind profiler was surrounded by a screen to reduce interference caused by ground clutter. The electromagnetic radiation from the wind profiler is sensitive to both Rayleigh scattering, from hydrometeors and Bragg scattering from refractive index inhomogenieties, on a scale of half a wavelength. In the lower troposphere the irregularities in refractive index are mainly caused by humidity fluctuations and to a lesser extent temperature changes. During field campaigns the wind profiler provides a picture of the meteorology over the site by providing detailed profiles of the three components of wind between altitudes of 75m and 3.5 km, depending on atmospheric conditions. During CSIP and COPS the wind profiler provided a particularly important role in identifying the altitude of temperature inversions that acted as lids to convective development. On occasions the wind profiler was used to resolve thermals as they drifted over the wind profiler. In addition, the location and strength of the turbulence was inferred from the spectral width of the Doppler signal. This poster shows some snap shots of measurements from the wind profiler during CSIP and COPS.

Emily Grace Norton 1,Alan Blyth 2,Andrew Russell 1,Geraint Vaughan1, Dave Wareing1,Catherine Gaffard 3

1. School of Earth Atmospheric and Environmental Sciences, University of Manchester, UK

2. School of Earth and Environment, University of Leeds, UK, 3. Met Office, Reading, UK

Figure 1: a) Outside view of the Clutter screen built during CSIP to surround the wind profiler. It consisted of a 2 m high curved clutter screen made out of corrugated metal from an old silage container b) View of the inside of the clutter screen.

The FGAM mobile wind profiler is a ‘clear-air’ UHF Doppler radar manufactured by Degreane Horizon. It operates at frequency of 1290 MHz twenty four hours a day. The wind profiler consists of three antennas one vertical and two orthogonal at an elevation of 73o . The Doppler shift associated with the turbulence provides a direct measurement of the mean radial velocity along the radar beam. Measurements in three independent directions enable full wind vectors (zonal, meridional and vertical) to be calculated.

Specifications of the FGAM wind profiler

DEGREANEHORIZON

Figure 2: a) Scale drawing plan of the clutter screen. b) Photo of the wind profiler at Achern during COPS surrounded by clutter screen made from wood and ½ inch steel wire mesh. The sides are angled at 170 from vertical

Figure 3: A typical plot of radial velocity verses altitude during COPS. Note there is very little ground clutter evident

Thermals observed during CSIP – 13th July 2005 - IOP 8

Figure 4 a) Shows the minimum signal to noise ratio (SNR) of the three beams as a function of altitude over a half hour period.  An inverted cup pattern was observed as the thermal drifted over the wind profiler. There are sharp abrupt changes in the humidity at the edges of thermals and cumulus clouds due to mixing and this causes sharp gradients of refractive index that results in the strong Bragg-scattering signal. The cores are more uniform as they are protected from entrainment and mixing hence Bragg scattering is weak. b) Shows the vertical velocity as a function of altitude over the same time period. The updraft in the core of this thermal, typical of the day, reached a maximum of 1.3 m s-1. The updrafts typically lasted approximately 7 minutes. From the average wind speed (2-3 m s-1) the horizontal extent of this updraft was estimated to be approximately 850-1260 m. The vertical extent of the updraft was approximately 1.4 km corresponding to the height of the cloud base which corresponded to a temperature inversion suppressing the convection The downdraughts associated with the thermals were weaker, approximately -0.8 m s-1and less distinct than the up draught.

Convection developed in the CSIP area on 13 July 2005 in a region of high moisture just north of Chilbolton near the wind profiler site.  Cumulus congestus clouds eventually grew to 5 km, but only a few light showers were observed north east of the CSIP area. A sea breeze front advanced northwards from the south coast.  Convection became deeper along the front, but the clouds were still not deep enough to produceprecipitation. Convection was suppressed behind the front.  Winds were light on this day, so thermals and cumulus clouds drifted slowly over the wind profiler and could be detected with the 2-min averaging.

Combining the strengths of UMIST andThe Victoria University of Manchester

Wind profiler plots of vertical velocity

On the 15th July 2007 deep convection developed east of the Black Forest crest, although convective available potential energy was moderate and convective inhibition was high. Figure 5 a) A plot of the signal to noise ratio of the clear air echo shows a layered structure to the planetary boundary layer. b) A plot of the vertical velocity show a series of updrafts as they drift over the site. Notice at 15:20 the updraft penetrates the capping inversion of the planetary boundary layer and extends to a vertical height of more than 3.8 km.

Thermals observed during COPS 15th July 2007 – IOP 8b

19th July 2007 – IOP 9bA large scale mesoscale convective system (MCS) was affecting the COPS region 6-12 UTC. The orography of the region had a significant effect on the modulation and the precipitation distribution of the system. After passing the COPS region strong convective cells were triggered in south East Germany.

Figure 6: a) Plot of the minimum signal to noise ratio (SNR) of the radar echoes such as these are useful for identifying lids in the atmosphere and defining the planetary boundary layer.

b) Plot of wind speed with wind direction arrows superimposed. This plot shows low winds beneath higher winds. The winds below 2km on this day changed from south easterly to southerly to westerly between 6:00 UTC and 14:00 UTC.

c) Plot of the vertical velocity calculated from the wind profiler. The black areas on this plot show bands of precipitation. The red areas show updrafts and the blue areas show the down drafts.

}Melting layer at 3km

23rd July 2007 – IOP 10• Figure 7: Time series of signal to noise ratio of the radar echos on 23rd July 2007. a) shows data from the high mode b) shows data

from the low mode. The plots highlight the advantage of having two measurement modes.

a) High mode

b) Low mode

The map above shows the locations of the COPS supersites. The wind profiler was run continuously between 13th June and 6th August 2007 during COPS at supersite R. Supersite R is located at Achern, Southern Germany (latitude 48.6 N, longitude 8.06 E) in the lowlands of the Rhine valley. This area is characterised by mainly homogeneous surfaces, the only landscape differences arising from variations in land use.

The map above shows CSIP measurement sites. The wind profiler was run continuously between during both parts of CSIP 6th July to 22nd July 2004 for the pilot campaign and16th June to 19th August 2005 for the main campaign. During the main CSIP campaign the wind profiler was located at Linkenholt (latitude 51.314 N, longitude1.475 W) approximately 18 km north of Chilbolton shown as the green spot on the main map.

During the pilot campaign the wind profiler was at Ashmansworth close to Linkenholt.

Map right to show the deployments the FGAM

wind profiler.

Papers to date from CSIP using the wind profiler data.Convection forced by a descending dry layer and low-level moist convergence Author(s): Russell A, Vaughan G, Norton EG, Ricketts HMA, Morcrette CJ, Hewison TJ, Browning KA, Blyth AM, Source: TELLUS SERIES A-DYNAMIC METEOROLOGY AND OCEANOGRAPHY    Volume: 61    Issue: 2    Pages: 250-263    Published: MAR 2009  

Observations of the development of convection through a series of stable layers during the Convective Storm Initiation Project Author(s): Bennett LJ, Blyth AM, Browning KA, Norton EG Source: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY    Volume: 134    Issue: 637    Pages: 2079-2091    Part: Part B    Published: OCT 2008  

Convective inhibition beneath an upper-level PV anomaly Author(s): Russell A, Vaughan G, Norton EG, Morcrette CJ, Browning KA, Blyth AM Source: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY    Volume: 134    Issue: 631    Pages: 371-383    Part: Part B    Published: JAN 2008  

Application of the Aventech AIMMS20AQ airborne probe for turbulence measurements during the Convective Storm Initiation Project Author(s): Beswick KM, Gallagher MW, Webb AR, Norton EG, Perry F Source: ATMOSPHERIC CHEMISTRY AND PHYSICS    Volume: 8    Issue: 17    Pages: 5449-5463    Published: 2008  

The Convective Storm Initiation Project Author(s): Browning KA, Blyth AM, Clark PA, Corsmeier U, Morcrette CJ, Agnew JL, Ballard SP, Bamber D, Barthlott C, et al Source: BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY    Volume: 88    Issue: 12    Pages: 1939-+    Published: DEC 2007  

Variable cirrus shading during CSIP IOP 5. II: Effects on the convective boundary layer Author(s): Marsham JH, Blyth AM, Parker DJ, Beswick K, Browning KA, Corsmeier U, Kalthoff N, Khodayar S, Morcrette CJ, Norton EG Source: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY    Volume: 133    Issue: 628    Pages: 1661-1675    Part: Part A    Published: OCT 2007  

Secondary initiation of multiple bands of cumulonimbus over southern Britain. I: An observational case-study Author(s): Morcrette CJ, Browning KA, Blyth AM, Bozier KE, Clark PA, Ladd D, Norton EG, Pavelin E Source: QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY    Volume: 132    Issue: 617    Pages: 1021-1051    Part: Part B    Published: APR 2006  

Multi-sensor observations of a wave beneath an impacting rear-inflow jet in an elevated mesoscale convective system John Marsham, Keith Browning, John Nicol, Emily Norton, Alan Blyth, Doug Parker et al.

http://www.cas.manchester.ac.uk/research/facilities/ufam/instrumenttable/windprofiler/http://www.ncas.ac.uk/fgam/

AcknowledgementsAll the many participants of CSIP, COPS and Philipp Currier from Degreane.

Funding from NCAS, NERC

Data storage British Atmospheric Data Centre (BADC)

Combining the strengths of UMIST andThe Victoria University of Manchester