Advances in Earth Science ›› 2013, Vol. 28 ›› Issue (6): 685-694. doi: 10.11867/j.issn.1001-8166.2013.06.0685

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Advances in Measurement Techniques and Statistics Features

Zhu Yaqiao 1,2, Liu Yuanbo 1   

  1. 1.Nanjing Institute of Geography and Limnology,Chinese Academy of Sciences,Nanjing210008,China;2.University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2013-01-16 Revised:2013-04-19 Online:2013-06-10 Published:2013-06-10

Zhu Yaqiao, Liu Yuanbo. Advances in Measurement Techniques and Statistics Features[J]. Advances in Earth Science, 2013, 28(6): 685-694.

 Rain Drop Size Distribution (DSD) is one of the key parameters to microphysical process and macrodynamical structure of precipitation. It provides useful information for understanding the mechanisms of precipitation formation and development. Conventional measurement techniques include momentum method, flour method, filtering paper, raindrop camera and immersion method. In general, the techniques have  large measurement error, heavy workload, and low efficiency. Innovation of disdrometer is a remarkable progress in DSD observation. To date, the major techniques are classified into impacting, optical and acoustic disdrometers, which are automated and more convenient and accurate. The impacting disdrometer transforms the momentum of raindrops into electric impulse, which are easy to operate and qualityassured but with large errors for extremely large or small raindrops. The optical disdrometer measures rainfall diameter and its velocity in the same time, but cannot distinguish the particles passing through sampling area simultaneously. The acoustic disdrometer determines DSD from the raindrop impacts on water body with a high temporal resolution but easily affected by wind. In addition, the Doppler can provide DSD with polarimetric techniques for large area while it is affected by updrafts, downdrafts and horizontal winds.DSD has meteorological features, which can be described with the MarshallPalmer (M-P), the Gamma, the lognormal or the normalized models. The MP model is suitable for steady rainfall, usually used for weak and moderate rainfall. The gamma model is proposed for DSD at high rain rate. The lognormal model is widely applied for cloud droplet analysis, but not appropriate for DSD with a broad spectrum. The normalized model is free of assumptions about the shape of the DSD. For practical application, statistical comparison is necessary for selection of a most suitable model. Meteorologically, convective rain has a relatively narrow and smooth DSD spectrum usually described by the MP model. Stratiform rain has a broad DSD spectrum described with the Gamma model. Stratocumulus mixed rain has relatively large drop diameter but small mean size usually described by the Gamma model. The continent rainfall is altitude dependent and it differs from the maritime cloud rainfalls in terms of rain rate and drop diameter. Overall, the meteorological features are useful to improve our understanding of precipitation formation but also important to development of precipitation retrieval techniques with a high accuracy.

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