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The growth of large hail within a steady updraught
Author(s) -
Browning K. A.
Publication year - 1963
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49708938206
Subject(s) - airflow , supercell , environmental science , inflow , meteorology , storm , atmospheric sciences , mechanics , geology , physics , thermodynamics
An analysis of the large‐scale organization of the Wokingham storm (Browning 1962b) shows that one of its constituent cells was particularly large and persistent. Throughout a 30‐min period, when it was most intense and producing the largest hail, this ‘Supercell’ exhibited a fairly steady structure which has been used to derive a model of the associated airflow (Browning and Ludlam 1962). In Part I of the present paper this model is given a quantitative basis. As a first approximation it is assumed that the airflow was two‐dimensional, but since the resulting model fails to account for the observed durations at the ground of hail and heavy rain it is modified to take into account a substantial convergent inflow towards the updraught from the right flank and towards the downdraught from the left flank. By applying and extending the analysis of hailstone growth within steady updraughts presented by Browning, Ludlam and Macklin (1963) and by relating it to the model of the airflow, it has been possible in Part II of this paper to account for the growth and the observed distribution of hail within the Wokingham storm. Two of the largest hailstones recovered are considered in detail because their structure can be explained only in terms of rather specific airflow characteristics. Their growth is shown to be consistent with the assumed vertical airspeeds within the updraught. Consideration of their growth‐times along with the distribution of hail at the ground suggests the presence within the updraught of horizontal components of motion relative to the storm of about 7 m sec −1 both towards its rear and towards its left flank. Finally, the existence is inferred of an abundant source of hailstone embryos owing to hailstones of all sizes re‐entering the foot of the updraught at levels above 4 km.