Numerical simulation of a low-level jet over complex terrain in southern Iran

The Lut Desert of iran is an elongated valley oriented north-northwest to s outh-southeast. The valley descends southward to the Jaz Murian dry lake th rough a pass. The Navy's Coupled Ocean-Atmosphere Mesoscale Prediction Syst em is used to study a northerly low-level jet in the valley and across the dry lake. The dynamics of the jet are investigated with force balance and F roude numbers to determine the contribution of various mechanisms to the je t formation and maintenance. The jet is initiated as a channeled gap flow i n the convergent topography of the Lut valley by the valley-parallel pressu re gradients generated by the large-scale processes and by the presence of cold air over the valley's sloping terrain; The pressure gradient is mainly counteracted by the frictional force. The imbalance between them controls the intensity and persistence of the jet in the valley Farther south, the j et evolves into a downslope Row resembling a hydraulic jump on the steep sl ope of the dry lake. A transition of subcritical situation to supercritical faster flow is Found at the mountain crest between the Lut valley and dry lake. The depth of stably stratified cold layer, the static stability of up stream inversion, and magnitude of upstream winds all determine the jet con figuration over the dry lake. The lee troughing over the Gulf of Oman and t he Persian Gulf, as the large-scale inland flow crosses the coastal mountai ns, supports this low-level jet through the increased along-jet pressure gr adient. The jet is also influenced by diurnal forcing, being strong at nigh t and weak during daytime.