Weather and Climate Modelling (WCM): Extreme Events

Mesoscale Modelling and Weather Prediction:

Climate and Weather phenomena of the tropics of varying time and spatial scales, namely, the Inter Tropical Convergence Zones (ITCZ), the monsoons, the Madden-Julian oscillations, the lows, the depressions, the cyclones and the localized high impact weather systems such as thunderstorms, etc., are ultimately mesoscale and convective in nature. Therefore, it is important to understand the interactions between the mesoscale systems and their environment in order to parameterize the mesoscale influences on the large scale. On the other hand, it is very essential to understand the micro-cloud-mesoscale interactions to unravel the genesis or the triggering mechanisms of convective systems and their intensity modulations. It is also necessary to study the turbulent processes and large-scale organized vortices in the Atmospheric Boundary Layer (ABL) aiming at their parameterization in models of weather and climate prediction of sub-kilometer spatial resolution. Importance of the problem is driven by the practical need to carry out a forecast at sub-kilometer resolution. Much attention should be paid to studying the large-scale turbulence spectra in ABL and the influence of turbulence closures and approximation errors of numerical schemes on the spectra reproduction.
Accurate weather prediction in the tropics on short and medium range time scales using dynamical models is a challenging task even today. A major uncertainty in the present weather prediction models lies in accurate representation of mechanisms for convective triggering and the appropriate physics parameterization schemes for the location of specific weather phenomena. In particular, it is necessary to focus on parameterization of mixing in convective and convective-shear ABL, taking into account the heterogeneity of the underlying surface, the radiative heat sources and the moisture phase transitions in the cloud layer. A major limitation for accurate weather prediction has been attributed to the model initial conditions not being well resolved in space and time, making them unable to capture the basic scales embedded in the phenomena. The applicability of most common models of turbulent mixing in the “gray zone” of atmospheric turbulence (100 m – 1 km) should be proven and the assessment of potential errors associated with the violation of the assumption of the separation of temporal and spatial scales needs to be done. These requirements triggered the major international programmes such as THORpex, YOTC, AMMA, which emphasized on enhancing the density of quality data with the focus on physical processes, and several national field programmes, PRWONAM, BOBMEX, ARMEX, LASPEX-97 and MONTBLEX-90, which aimed at improving the short term weather prediction and the physics parameterization schemes over the land and sea.

The primary Goals here are

  • Understanding atmospheric processes at higher resolution for regional atmospheric modeling studies using space and field based observations for applications in improved short term weather prediction.
  • To articulate the scientific issues driving tropical circulation and energetics and to relate them to mesoscale atmospheric modeling studies.
  • To simulate processes in ABL, particularly the large-scale organized vortices, comparable in size to the grid spacing of atmospheric mesoscale numerical models.
  • Assimilation of data from mesoscale observational networks in the country for a reliable operational weather forecast system.
  • To design field experiments to understand the initiation of tropical convection and to develop, verify parameterization schemes to be incorporated in atmospheric models to simulate weather and climate variability.