EGU21-15444
https://doi.org/10.5194/egusphere-egu21-15444
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Precipitation modes over the Western Ghats orography during the summer monsoon season

Jayesh Phadtare1,2, Jennifer Fletcher3, Andrew Ross4, Andy Turner5, Thorwald Stein6, and Reinhard Schiemann7
Jayesh Phadtare et al.
  • 1School of Earth and Environment, University of Leeds, Leeds, UK (j.phadtare@leeds.ac.uk)
  • 2National Centre for Atmospheric Science, University of Leeds, Leeds, UK (jayesh.phadtare@ncas.ac.uk)
  • 3School of Earth and Environment, University of Leeds, Leeds, UK (j.k.fletcher@leeds.ac.uk)
  • 4School of Earth and Environment, University of Leeds, Leeds, UK (a.n.ross@leeds.ac.uk)
  • 5Department of Meteorology, University of Reading, Reading, UK (a.g.turner@reading.ac.uk)
  • 6Department of Meteorology, University of Reading, Reading, UK (t.h.m.stein@reading.ac.uk)
  • 7Department of Meteorology, University of Reading, Reading, UK (r.k.schiemann@reading.ac.uk)

Precipitation distribution around an orographic barrier is controlled by the Froude Number (Fr) of the impinging flow. Fr is essentially a ratio of kinetic energy and stratification of winds around the orography. For Fr > 1 (Fr <1), the flow is unblocked (blocked) and precipitation occurs over the mountain peaks and the lee region (upwind region). While idealized modelling studies have robustly established this relationship, its widespread real-world application is hampered by the dearth of relevant observations. Nevertheless, the data collected in the field campaigns give us an opportunity to explore this relationship and provide a testbed for numerical models. A realistic distribution of precipitation over a mountainous region in these models is necessary for flash-flood and landslide forecasting. The Western Ghats region is a classic example where the orographically induced precipitation leads to floods and landslides during the summer monsoon season. In the recent INCOMPASS field campaign, it was shown that the precipitation over the west coast of India occurred in alternate offshore and onshore phases. The Western Ghats received precipitation predominantly during the onshore phase which was characterized by a stronger westerly flow. Here, using the radiosonde data from a station over the Indian west coast and IMERG precipitation product, we show that climatologically, these phases can be mapped over an Fr-based classification of the monsoonal westerly flow. Classifying the flow as 'High Fr' (Fr >1), 'Moderate Fr' ( 0.5 < Fr ≤ 1) and 'Low Fr' ( Fr ≤ 0.5 ) gives three topographical modes of precipitation -- 'Orographic', 'Coastal' and 'Offshore', respectively.  Moreover, these modes are not sensitive to the choice of radiosonde station over the west coast.

How to cite: Phadtare, J., Fletcher, J., Ross, A., Turner, A., Stein, T., and Schiemann, R.: Precipitation modes over the Western Ghats orography during the summer monsoon season, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15444, https://doi.org/10.5194/egusphere-egu21-15444, 2021.

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