Pinhas Alpert*, N. Halfon, Z. Levin

*Corresponding author for this work

Research output: Contribution to journalComment/debate


Putting the new analysis of GR09 in a spatial context shows that in agreement with AHL08 no decrease is observed in the orographic precipitation ratio between the stations on the upslope and those at the seashore. The decreases in Ro that GR09 found are restricted to the eastern slopes of the Galilee Mountains. This contradicts the theory of rainfall suppression presented by GR04 that claims that the decrease in rainfall is found on the western upslope of the mountains. Furthermore, this finding contradicts the claim by GR05 that argues that cloud seeding, which is aimed at increasing rainfall on the eastern slopes of the Galilee Mountains, reaches its maximum impact in regions affected by orographic clouds. Both GR09 and AHL08 found that a few kilometers downwind of the seashore line and the adjacent urban centers there is a slight increase in annual rainfall. It is therefore clear that calculating Ro between the mountain stations and this region shows a slight decrease due to the larger value in the denominator. Since the results of GR09 confirm those of AHL08, we do not think it is valuable to repeat our discussion and the reasons why the theory presented by GR04 and GR05 is not valid (at least for Israel); we refer the reader to the original paper of AHL08. Regarding the increase in rainfall downwind of the seashore, AHL08 raised the hypothesis that at least in part it could be related to urban effects. This idea has been shown to occur in other urban environments and was also shown by others to occur in central Israel (AHL08 and references therein). We did not, however, rule out other reasons for this observed increase. In summary, we do not rule out the fact that aerosol pollution has some microphysical effects on precipitation, but we argue that other, probably dynamical, factors are much stronger and overshadow the effects of aerosols. This makes the job of identifying the aerosol effects much more complicated, as discussed with a full historical perspective by Levin and Cotton (2008).

Original languageEnglish
Pages (from-to)1751-1754
Number of pages4
JournalJournal of Applied Meteorology and Climatology
Issue number8
StatePublished - 2009


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