عنوان مقاله [English]
Gonu storm was formed in tropical basin of Indian Ocean early in June 2007. Gonu is the strongest tropical cyclone that happened in Arabian Sea and North Indian Ocean and moved toward Oman Sea and Persian Gulf and bouncing the lands around the area. This tropical cyclone made extensive damages and human and financial causalities to countries of Oman, Iran, Afghanistan, Pakistan, and India.
In this study, an analytical model (Kiue et al., 2010) is applied to the tropical cyclone of Gonu to examine the predicted surface pressure and tangential wind velocity relation. This model is an analytical model includes momentum equation in polar coordinates with a primary hypothesis of the wind blowing is in a Rankine vortex regime. The pattern of surface wind speeds in tropical cyclone complies with the Rankin function, so that in the inner core region, the tangential and radial wind velocity increases linearly with increasing of the radius, and wind speed in the external region is decreasing as radius increases. To examine the dynamic model (Kiue), first the pressure reduction is calculated by this model for Gonu tropical cyclone. Then the minimum sea level pressure is compared with the equivalent reported pressure by Joint Typhoon Warning Center (JTWC). The results show that the model is capable of predicting the magnitude of falling pressure of tropical cyclone Gonu. Then to investigate the role of different forces on the formation and development of this tropical cyclone, the proposed equation by Kiue was applied and 3 forces of centrifugal, Coriolis and frictional were calculated and also the contribution of those forces on the falling of the pressure in eye of cyclones were computed. It is revealed that the weight of centrifugal force effect is dominant.
The data used in this study to examine the analytical model of Kiue, is Gono cyclone best track of JTWC database. The JTWC is the Joint committee of the US Air Force and Marine to warn hurricanes formation and development. It measures the intensity of the storm via Dvorak (1974) method. This study does not mention how this method works, but the Dvorak method is based on satellite imagery, which is operational in most of the storm warning centers.
In this study, we also run the ARPS and WRF models and to verify that if calculated surface wind speed of these models for cyclone Gonu is comparable to JTWC database weather they can estimate the intensity of this tropical cyclone. The results show that the surface wind speed output of WRF models do not show the way of Gonu formation. In addition, the maximum surface wind (VMAX) shows that Gonu did not convert to a tropical cyclone as well. According to the results of ARP's model, maximum surface wind (VMAX) is calculated about 82 m/s. However, it has about 9.5 m/s discrepancy with maximum surface wind (VMAX) of JTWS for Gonu. However, this speed shows that the Gonu cyclone is reached to category five hurricanes and converted to a tropical cyclone. Therefore, the model ARPS is more successful.