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W. L. Physick
and
N. J. Tapper

Abstract

Observations of surface winds in the vicinity of a moderate-sized (about 70 km2) dry salt lake by Tapper suggest that differences in albedo and soil thermal properties between the salt and surrounding sand surfaces may be strong enough to drive a mesoscale thermal circulation. In this paper a numerical mesoscale model is used to investigate disturbances generated by moderate and large-sized (about 7000 km2) lakes. In the latter case, a typical size for the great salt lakes of inland Australia, disturbances with strong horizontal and vertical shear are found at a distance of more than 200 km from the lakeshore by midnight. The separate contribution of albedo and soil property differences to the circulation are assessed, under both dry and moist soil conditions. The possible influence of such circulations on regional climate is discussed and it is suggested that salt lakes may be a source for solitary waves observed in the Australian interior.

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N. J. Tapper
,
P. D. Tyson
,
I. F. Owens
, and
W. J. Hastie

Abstract

An energy balance model is presented and tested against surface temperature fields observed over Christchurch under clear winter conditions. The fit between observed and simulated fields is shown to be close by night and slightly less so by day. Using the model the spatial variation of net radiation, sensible, latent and substrate heat fluxes within the Christchurch urban heat island is illustrated for average winter cloudless days and nights.

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T. Keenan
,
S. Rutledge
,
R. Carbone
,
J. Wilson
,
T. Takahashi
,
P. May
,
N. Tapper
,
M. Platt
,
J. Hacker
,
S. Sekelsky
,
M. Moncrieff
,
K. Saito
,
G. Holland
,
A. Crook
, and
K. Gage

A description is given of the Maritime Continent Thunderstorm Experiment held over the Tiwi Islands (12°S, 130°E) during the period November–December 1995. The unique nature of regularly occurring storms over these islands enabled a study principally aimed at investigating the life cycle of island-initiated mesoscale convective systems within the Maritime Continent. The program objectives are first outlined and then selected results from various observationally based and modeling studies are summarized.

These storms are shown to depend typically on island-scale forcing although external mesoscale disturbances can result in significant storm activity as they pass over the heated island. Particular emphasis is given to summarizing the environmental characteristics and the impact this has on the location of storm development and the associated rainfall distribution.

The mean rainfall production from these storms is shown to be about 760 × 105 m3, with considerable variability. The mesoscale evolution is summarized and during the rapid development phase the interaction of storms with preexisting convergence zones is highlighted. In situ microphysical observations show the occurrence of very large rain drops (up to 8-mm diameter) and very large concentrations of ice crystals in the −10° to −60°C temperature range associated with the very intense updrafts. Occurrence of graupel aloft is shown to be strongly linked to cloud to ground lightning. Polarimetric radar-based rainfall estimates using specific differential phase shift are shown to be considerably better than reflectivity based estimates. Studies relating to the structure of anvil cloud and the effect on the radiative heating profile are also summarized. Initial attempts at modeling storm development are also presented. Two different nonhydrostatic models on days with markedly different evolution are employed and indicate that the models show considerable promise in their ability to develop mesoscale systems. However, important differences still remain between observed storm evolution and that modeled.

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