TY - JOUR

T1 - Analyzing the relationship between terminal velocity of raindrops and VHF backscatter from precipitation

AU - Su, Ching Lun

AU - Chu, Yen Hsyang

AU - Chen, Chun Yi

PY - 2004/11

Y1 - 2004/11

N2 - The exponential relationship between α and β in the expression VT = αPβ was first found empirically by Chu et al. (1999), where VT is the mean Doppler velocity of the rain drop with respect to still air, and P is the range-corrected VHF radar backscatter from precipitation. However, they did not provide a theoretical explanation for this relationship. In this article, we will show theoretically that the mathematical relationship between α and β is indeed in an exponential form, namely, α = Aexp(-ξβ), where A is the coefficient in the relation V = ADB D is the diameter of the rain drop, and ξ is a factor related to radar parameters and precipitation intensity. An examination of this exponential relationship between α and β shows that the radar experimental result was in excellent agreement with the theoretical prediction. From the observational results made with the Chung-Li VHF radar, we find that the value of β varied in the range 0.02 - 0.14, which is significantly different from the theoretical value of 0.07143. In addition, the β value is found to be positively correlated with the vertical air velocity, which is variable in nature. We, therefore, presume that the vertical air velocity seems to play a crucial factor in governing the change in the β value to explain the large scatter of the observed β values. The application of ξ value to the estimation of the precipitation intensity is also discussed in the text.

AB - The exponential relationship between α and β in the expression VT = αPβ was first found empirically by Chu et al. (1999), where VT is the mean Doppler velocity of the rain drop with respect to still air, and P is the range-corrected VHF radar backscatter from precipitation. However, they did not provide a theoretical explanation for this relationship. In this article, we will show theoretically that the mathematical relationship between α and β is indeed in an exponential form, namely, α = Aexp(-ξβ), where A is the coefficient in the relation V = ADB D is the diameter of the rain drop, and ξ is a factor related to radar parameters and precipitation intensity. An examination of this exponential relationship between α and β shows that the radar experimental result was in excellent agreement with the theoretical prediction. From the observational results made with the Chung-Li VHF radar, we find that the value of β varied in the range 0.02 - 0.14, which is significantly different from the theoretical value of 0.07143. In addition, the β value is found to be positively correlated with the vertical air velocity, which is variable in nature. We, therefore, presume that the vertical air velocity seems to play a crucial factor in governing the change in the β value to explain the large scatter of the observed β values. The application of ξ value to the estimation of the precipitation intensity is also discussed in the text.

KW - Drop size distribution

KW - Terminal velocity

KW - VHF radar

UR - http://www.scopus.com/inward/record.url?scp=11144301372&partnerID=8YFLogxK

U2 - 10.3319/TAO.2004.15.4.629(A)

DO - 10.3319/TAO.2004.15.4.629(A)

M3 - 期刊論文

AN - SCOPUS:11144301372

SN - 1017-0839

VL - 15

SP - 629

EP - 645

JO - Terrestrial, Atmospheric and Oceanic Sciences

JF - Terrestrial, Atmospheric and Oceanic Sciences

IS - 4

ER -