Results from the ARM Mobile Facility

Transcription

1 AMMA Workshop, Toulouse, November 2006 Results from the ARM Mobile Facility Background Anthony Slingo Environmental Systems Science Centre University of Reading, UK Selected results, including a major dust storm in March 2006 Summary and future work

2 ARM Mobile Facility The AMF is operated by the US Atmospheric Radiation Measurement (ARM) program It was established in November 2005 and will continue to run until the end of 2006 the main site is at Niamey airport subsidiary site at Banizoumbou Wide range of instruments at the main site: including visible, infrared and microwave radiometers, infrared spectrometer (AERI), Lidars, Radar, aerosol sampling, standard meteorological instruments and radiosondes (four per day throughout the year)

3 Overview of the main site at Niamey airport. The instrument field (right) is located about 100m from the main facility (left)

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6 The RADAGAST project Radiative Atmospheric Divergence using ARM Mobile Facility, GERB data and AMMA stations led by Tony Slingo, ESSC, Reading University, UK Links the ARM Mobile Facility with GERB (Geostationary Earth Radiation Budget instrument on Meteosat) & AMMA The objective is to derive the divergence of radiation across the atmosphere: by combining the AMF measurements of the surface radiative fluxes and vertical structure of the atmosphere with GERB data from the top of the atmosphere and AMMA observations study the radiative properties of aerosols (desert dust, biomass), water vapour and clouds provide comprehensive observations for testing radiation codes

7 SEVIRI and GERB on Meteosat SEVIRI is the operational imager 12 narrow spectral channels covering solar (4 vis/nir) and thermal (8 IR) regions sub-satellite resolution ~1km / ~3km GERB measures the broadband radiation budget shortwave and total: μm and μm subtraction results in longwave: 4-30μm sub-satellite resolution is ~45km, but there is also an enhanced resolution product (~10km) using SEVIRI Both instruments have ~15 minute temporal resolution Meteosat-8 is the operational satellite, launched August 2002 Meteosat-9 launched December 2005 is currently backup

8 Column water vapour over Niamey (cm) Green: microwave radiometer Red: radiosondes J F M A M J J A S O

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12 Observations of the impact of a major Saharan dust storm on the atmospheric radiation balance A. Slingo 1, T.P. Ackerman 2, R.P. Allan 1, E.I. Kassianov 2, S.A. Mcfarlane 2, G.J. Robinson 1, J.C. Barnard 2, M.A. Miller 3, J.E. Harries 4, J.E. Russell 4 & S. Dewitte 5 Geophysical Research Letters, in press

13 In these false-colour images, the dust appears pink or magenta, water vapour dark blue, thick high-level clouds red-brown, thin high-level clouds almost black and surface features pale blue or purple. On 6 March, unusually strong northerly winds bring cold air at low levels over the desert, creating a broad front of dust as the air moves south. 1200GMT, 6 March 2006 The location of Niamey is marked by a cross.

14 In these false-colour images, the dust appears pink or magenta, water vapour dark blue, thick high-level clouds red-brown, thin high-level clouds almost black and surface features pale blue or purple. 1200GMT, 7 March 2006 The shallow layer of cold air cannot rise over the mountains of the central Sahara (light blue in colour), so it is forced to follow the valleys. Streaks appear where it accelerates through gaps in the topography. The dust reached Niamey at 0930 on 7 March.

15 In these false-colour images, the dust appears pink or magenta, water vapour dark blue, thick high-level clouds red-brown, thin high-level clouds almost black and surface features pale blue or purple. By 8 March, dust covers the whole of West Africa and is moving out over the Atlantic. 1200GMT, 8 March 2006

16 Dust product (upper) and GERB OLR (lower) for 1200UT on 8 March 2006 Cloud Dust Lake Chad

17 Animation of Meteosat dust product

18 Radiosonde ascent, 6 March 2006, prior to dust storm

19 Radiosonde ascent, 8 March 2006, during dust storm

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23 Dust product: 1215 GMT on 6 November 2006

24 Summary and future work Excellent data from the Mobile Facility, GERB and SEVIRI overview paper in Bulletin of the American Meteorological Society ARM data are freely available: see Major dust storm in March 2006 large perturbations to solar and thermal fluxes at both the surface and at the top of the atmosphere significant increase in atmospheric solar absorption, which is underestimated by the radiation models paper in press in Geophysical Research Letters Ongoing work includes: continue to monitor events and to identify test cases quicklooks on Radagast website collaboration with Met Office (SOP0), ARM (radiative divergence), Eumetsat Climate SAF (surface radiation budget) and others developing the methodology to derive area-average surface fluxes and to exploit the data from the second site at Banizoumbou