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Using the MRR for studying the bright band, drop size distribution and now-casting
What is the bright band?The bright band is the region in the atmosphere where frozen particles melt into rain and this gives a stronger radar reflection than the regions of frozen particles above and rain below. It is also referred to as the melting layer or freezing layer.
Using the Micro Rain Radar to study the Bright BandThe Micro Rain Radar can be used to observe the atmospheric freezing layer to gain a greater understanding of the modifying influence (if any) of precipitation. Awareness of the bright band has been around for quite some time and operationally forecasters as well as the computer modelling community use this information to aid them in their work. The latest thoughts on the development of the bright band are that precipitation just below the bright band has a modifying affect on the freezing level itself and can contribute significantly to the rapid decay of the freezing level height. Previously this has been very hard or near impossible to observe operationally and especially repeatedly but now using the latest technology of the Micro Rain Radar (MRR), a newly released and unique precipitation measurement device, several users are finding this a cost effective way (prices start from £14k) at looking into this phenomenon. By using the MRR they hope to gain a greater understanding of the modifying influence (if any) of precipitation just below the bright band on the bright band itself. Studies in the UK and USA have been running for just over a year now on this area and together with another winter seasons’ data it is hoped that some first patterns can be understood, analysed and published then integrated into operational weather models for forecasting with greater precision. Drop Size Distributions (DSD)In the vertical profiles of drop size distribution below the x axis = drop diameter y axis = height above radar. The colours indicate the number of drops per size interval
For studies into drop size distribution many users are finding the Micro Rain Radar a useful tool. The MRR is not influenced by ambient wind conditions and therefore provides far more accurate drop size distributions than typical 'point' optical disdrometers as well as additionally giving a complete vertical profile of the precipitation. Unlike other 'normal' radars the MRR does not calculate DSD from reflectivity data but inherently measures the precipitation size and from this the terminal fall velocity can be exploited from the drop size diameter. Once this relationship has been established the accumulation rates, drop size distributions, liquid water content amounts, among other derived parameters can be found allowing a far better understanding of the development of the precipitation as it passes overhead. The MRR is able to produce 30 range heights for measurements with a spacing of between 30 m and 200 m, giving a range potential of 1 Km using a 30 m resolution and up to 6 Km using a 200m resolution.
Now-casting of precipitation is the detection of rain before it reaches the ground. Usually the rain starts high above the ground and due to evaporation processes it takes some time until it starts to rain at ground level. The MRR is able to detect the rain high above the ground and depending on the height at which the rain is detected it will give an advantage of 5 to 10 minutes before it rains at ground level. |
