Moist Potential Vorticity Vector for Diagnosis of Heavy Rainfall Events in Tanzania

Abstract

In this paper, we modify the convective vorticity vector (CVV) defined as a cross product of absolute vorticity and gradient of equivalent potential temperature to moist potential vorticity vector () MPVV defined as a cross product of absolute vorticity (a ζ) and the gradient of the moist-air entropy potential temperature (s θ). The patterns of () MPVV are compared with the patterns of heavy rainfall events that occurred over different regions in Tanzania on 20 th to 22 nd December, 2011 and on 5 th to 8 th May, 2015. Moreover, the article aimed at assessing the relative contributions of the magnitude, horizontal and vertical components of () MPVV detecting on the observed patterns of rainfall events. Dynamic and thermodynamic variables: wind speed, temperature, atmospheric pressure and relative humidity from numerical output generated by the Weather Research and Forecasting (WRF) model running at Tanzania Meteorological Agency (TMA) were used to compute. MPVV It is found that MPVV provide accurate tracking of locations received heavy rainfall, suggesting its potential use as a dynamic tracer for heavy rainfall events in Tanzania. Finally it is found that the first and second components of MPVV contribute almost equally in tracing locations received heavy rainfall events. The magnitude of MPVV described the locations received heavy rainfall events better than the components.

Impacts of Projected Urban Expansion on Rainfall and Temperature during Rainy Season in the Middle-Eastern Region in Tanzania

“…WRF is a non-hydrostatic, next-generation mesoscale NWP model that can simulate the complete set of atmospheric processes with optional adjustments to physics schemes, initialized boundary conditions and data assimilation [44]. This study adopted a similar WRF domain as used in the previous studies [39,[44][45][46][47].…”

The Use of Moist Potential Vorticity Vector as Diagnostic Variable of Rainfall Events in Tanzania

“…Gao et al (2004) suggested the use of Convective Vorticity Vector (CVV) while studying deep convection over the tropics. However CVV is defined using the gradient of equivalent potential temperature which is conserved only under moist adiabatic and frictionless atmospheric flow (Luhunga et al, 2016). Since the atmosphere is nonuniformly saturated, CVV cannot be used to study non-uniformly saturated atmospheric flow and fulfill at the same time the dry air and moist air conservative property (Luhunga et al, 2016).…”

Assessing Weather Research and Forecasting (WRF) Model Parameterization Schemes Skill to Simulate Extreme Rainfall Events over Dar es Salaam on 21 December 2011

“…In Tanzania, some studies have been conducted using WRF model such as Luhunga et al [7]; Kondowe et al [20] and Mlonganile et al [21]. Kondowe 2) Which combination of physical parameterization schemes accurately simulated the extreme rainfall event?…”

“…Extreme rainfall events that often occur in Dar es Salaam coastal city are influenced by variations of climate due to its physical topography, monsoon winds and ocean influences (Indian ocean) [6] [7]. About 8% of its land lies below 10 m above mean sea level and considering the low-lying nature of the coastal areas in the city, climate change and sea-level rise present additional flood major weather-related threats to the population, infrastructure and other scio-economic development in the coastal zone [8] [9].…”

“…In Tanzania, the complex topographical landscape, numerous large inland water bodies, variation in vegetation types and land-ocean contrast present additional difficult to forecast heavy rainfall [6] [7]. Therefore, investigations are required to understand the physical properties of small scale meteorological processes which have a great influence on the precipitation simulated and also play an important role in determining the vertical structure of temperature and moisture fields of the atmosphere [15].…”