Modelling Anomalous Weather Conditions over the Himalaya

• Author / Creator

  Tiwari, Ujjwal

• The Himalayan weather system is under the influence of both tropical and extratropical factors, and interactions between those factors can result in extreme weather-related disasters. However, due to an existing knowledge gap about the factors contributing to anomalous weather conditions over the Himalaya and very limited resources for weather forecasting, extreme weather prediction over the world's most extreme topography is very challenging. In this thesis, I used the combination of observations, reanalysis data, and mesoscale atmospheric model output to understand the influence of upper-tropospheric atmospheric blocks on anomalous weather conditions over the Himalaya. Furthermore, I evaluated the performance of various cloud-microphysics parameterization schemes and forcing data in the mesoscale atmospheric model to predict extreme precipitation events over the Himalaya. My results suggest that Ural-Siberian blocks are important perturbations to Himalayan weather and are associated with anomalous precipitation. The freezing level drops/rises depending on anomalous cold/warm advection triggered by the block, and this determines the type of precipitation (rain or snow) at different regions.
  Sensitivity tests of different cloud microphysics schemes and initial conditions with the WRF mesoscale atmospheric model, which was used to simulate an extreme flood-producing precipitation event on August 2017 over Nepal, showed that the coarse resolution (15 km) simulation with the WRF Single Moment Class 6 (WSM6) scheme forced with ERA-Interim data performed the best, but at, high-resolution (3 km) the WRF Double Moment Class 6 (WDM6) scheme forced with ERA-Interim data was closest to observations. The overall performance of coarse resolution simulations was found to be better than the high-resolution simulations that had the cumulus scheme turned off. To further understand the effectiveness of the cumulus parameterization below 5 km resolution, I performed two experiments at 3 km horizontal resolution using the WSM6 and WDM6 microphysics schemes forced with ERA-Interim data. There was an overall improvement in simulated precipitation with the WDM6 microphysics scheme when the cumulus parameterization was on. Thus, my result suggests the importance of keeping the cumulus parameterization on over regions that have steep topographic relief to accurately simulate the quantity of precipitation for such flood-producing events.

• Subjects / Keywords

  • Himalaya
  • Microphysics
  • Nepal
  • Atmospheric Block
  • WRF

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-afe4-xg74

• License

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