Identification of Mountain Waves and Their Characteristics in the Central Java Region based on the WRF Numerical Weather Model

Abstract

One of the factors that influence the complexity of the weather and climate phenomena in Indonesia is the diverse topographical conditions. The Mountain waves are quite common in Indonesia, especially on the island of Java, which has several mountains with quite high peaks. The existence of mountain waves can be known from the presence of lenticularis clouds both on top of the mountain are regularly reported by residents in the area of Mount Ungaran and Mount Lawu in Centra Java. This study utilized the Weather Reasearch Forecast (WRF), a numerical weather model to identify mountain waves and their characteristics in Mount Ungaran and Mount Lawu. The results of the study are that there were 2 mountain wave events in Mount Ungaran on 9 September 2018 with an average duration of 5 h, and horizontal wavelengths reaches 28 km. During that mountain wave events, there was also a type 1 rotor with dominant positive vorticity and a breaking pattern that indicates the potential for strong turbulence which is supported by critical Ri value at a distance of 30 - 90 m on the leeward side. Meanwhile, in Mount Lawu case on 9 March 2019, the mountain wave onset occurs during the day is in the afternoon, its duration is 2 h, wavelengths ranging from 5.9 to 6.1 km, where in the leeward side has no strong turbulence potential. In general, WRF can simulate both mountain waves and rotors, but has not been able to properly simulate the downslope windstorms. HIGHLIGHTS There were 2 mountain wave events that occurred at Mount Ungaran on 9 September 2018. The classification of mountain waves obtained from on cross section analysis of vertical wind speed around the mountain is vertically propagating wave The type of rotor formed at Mount Ungaran is a type 1 rotor a type 1 rotor with a dominant positive vorticity value In Mount Lawu case on 9 March 2019, the onset of waves occurred during the day and then dissipated in the afternoon with wavelengths ranging from 5.9 to 6.1 km In Mount Lawu case, on the leeward side of the mountain, there was no potential for turbulence at that location WRF can simulate mountain waves and rotors well, but can't simulate well the downslope windstorm on Mount Ungaran GRAPHICAL ABSTRACT