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UFAM 1275 MHz Clear-air Radar: ACROBATan Advanced Clear-air Radar for Observing the Boundary layer And Troposphere
Convection studiesACROBAT has proved to be an excellent tool for studying convective structures in the boundary layer. Since convection, by its very nature, is associated with strong temperature and humidity gradients, it leads to strong clear-air radar returns in the boundary layer. Convective structures lead to a characteristic pattern of arches and plumes in RHI scans of radar reflectivity. In PPI scans, convective elements are often visible as ring-shaped structures, indicating the strong refractive index gradients at the edges of individual convective cells. ACROBAT played a key role in the Convective Storm Initiation Project (CSIP) pilot campaign in Summer 2004. The radar will again provide real-time images of the evolution of convection during the main CSIP campaign in 2005.
Above: RHI scan from the ACROBAT radar on 10 July 2004 (during CSIP)
Refractivity measurementsThe ACROBAT radar transmitter and receiver are phase-locked to a stable frequency reference. This allows the radar to make accurate measurements of the phase of radar echo returns. Fabry et al. (1997) showed how such phase measurements can be used to measure fields of surface refractive index changes. By isolating the returns from stable ground clutter targets and tracking the phase of their radar returns with time, changes in refractive index in the paths between these targets can be monitored. This allows fields of refractivity variations to be obtained with an accuracy of a few parts per million.The radio refractive index of the atmosphere is highly dependent on humidity, and these refractivity measurements will be extremely useful in tracking humidity anomalies associated with the onset of convection and precipitation.
Above: Field of horizontal refractive index anomalies measured on 10 July
2004. The green band in the middle of the field (higher refractivity than
the surroundings) is associated with a convective system passing over
the radar site.
System status (18/11/04): The ACROBAT system is fully operational.
Click here for a technical overview of the radar system. We welcome suggestions from researchers wishing to use this facility. For more information, please contact the Instrument Scientist, Ed Pavelin (e.pavelin@reading.ac.uk, tel. 0118 378 7381).
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