Current
Dynamics of land-sea breezes in the tropics
In midlatitudes, where the inertial frequency (\(f\)) is greater than the frequency of the diurnal cycle (\(\omega\)), land-sea breezes are in phase with the heating/cooling of the land surface. In the tropics, \(f < \omega \). Therefore, the heating- and land-sea-breeze system can exhibit a phase lag depending on latitude. Furthermore, changes in the boundary-layer stratification (\(N\)) can alter turbulent friction, thereby causing inertial oscillations. Using simple models, I am analyzing what combinations of diurnal forcing and turbulent friction produce the observed land-sea breeze circulations in the tropics. A more ambitious goal is to add the effect of orography to this model.
Horizontal flow at 06 and 12 LST mimicking land-sea breeze circulation.
Role of atmospheric processes in the warming of oceans
This research is funded by the US Office of Naval Research (ONR). The overarching goal of this project is to understand the warming of the Indian Ocean during the pre-monsoon season. During this time of year, the Indian Ocean is the warmest ocean on our planet and profoundly affects the climate by energising monsoon winds and, in some years, tropical cyclones. The role of atmospheric and oceanic processes in the rapid warming of the Indian Ocean is not well understood. To this end, atmospheric and oceanic field observations were collected during May-June 2024 using shipboard instruments, buoys, and weather balloons (radiosondes) over the Indian Ocean and the Bay of Bengal. Quantities such as wind speed, cloud cover, radiation, sea surface temperature, and ocean currents were recorded. Our initial analysis suggests that the capping inversion over the marine atmospheric boundary layer plays a crucial role in the warming of the northern Indian Ocean during the pre-monsoon season. The strongest inversion is created along the coast, which is advected offshore by the prevailing winds.
Topographic steering of Convectively Coupled Kelvin Waves (CCKWs)
The Convectively Coupled Kelvin Waves (CCKWs) are eastward propagating tropical atmospheric waves with a period between 3 and 17 days, a wavelength of about 10,000 km, and a speed of about 15 m. These waves are responsible for the large-scale organization of tropical clouds/rainfall and play a significant role in the tropical climate. Previously, CCKWs were studied separately over Africa and the Indian Ocean. We studied the evolution of CCKWs propagating across the two regions. We show that the East African Highlands obstruct the passage of CCKWs and divert a part of the wave northwards, thus weakening the wave arriving over the Indian Ocean. This finding has important implications for understanding the fundamental dynamics of the tropical atmosphere.
Ref:
Phadtare, J. , Fernando, H.S.J. (2025), On the propagation of convectively coupled Kelvin Waves from Africa to the Indian Ocean. Geophys. Res. Lett. [Link]
Previous
Modelling Rainfall over the Western Ghats
The Western Ghats are one of the rainiest places on our planet. The low-level monsoon jet from the southwest brings loads of moisture over the west coast of India. The Western Ghats provide a mechanical uplifting mechanism for the advected warm and moist air parcels. Thus, the west coast of India is prone to life-threatening flooding during the summer monsoon months, as evidenced by the Mumbai flood in July 2005 and the Kerala flood in August 2018. My research at the National Centre for Atmospheric Science, University of Leeds, investigated the orographic effects of the Western Ghats on the West Coast rainfall and its representation in numerical models. It was concluded that a model resolution of O(1km) is needed to simulate the mean rainfall accumulation over the Western Ghats. However, even at this high resolution, models overestimate rainfall (by 50-100%) over the orography, especially during the phases of weak winds/offshore rainfall. This error stems from an anomalously weak orographic blocking effect in models.
Ref:
Phadtare, J., Fletcher, J.K., Ross, A.N., Turner, A.G., Schiemann, R.K., Burns. H., L. (2023). Unravelling the Mechanism of Summer Monsoon Rainfall Modes over the West Coast of India using Model Simulations, Q. J. Roy. Meteor. Soc. .
Phadtare, J., Fletcher, J.K., Ross, A.N., Turner, A.G. and Schiemann, R.K., 2022. Froude number-based Rainfall Regimes over the Western Ghats Mountains of India. Q. J. Roy. Meteor. Soc.
Influence of Underlying Orography on Cyclonic Systems
The east coast of India is prone to extreme floods during the winter monsoon, e.g., the 2015 South India floods. The influence of the Western Ghats on the west coast rainfall has been known for a very long time. However, the role of the Eastern Ghats on East Coast rainfall was recently discovered in a study by Phadtare (2018). Even though the Eastern Ghats lie about 200 km inland from the coast, the orographic effect is conveyed through the cold pool, a 'thermodynamic mountain'. In a weak background flow, tropical cyclones move westward due to the planetary β effect. Therefore, cyclonic storms that form over the eastern Indian Ocean-Maritime Continent region tend to reach the east coasts of India and Sri Lanka. Some of these storms stall over the coast, causing catastrophic flooding for several days. The goal of this research was to identify the causes of the stagnation of these cyclonic storms, enabling better forecasting of severe flooding events and preventing loss of life. Initial investigations suggest that the weaker storms are blocked by the Eastern Ghats orographic range (Phadtare, 2018, 2023).
Ref:
Phadtare, J. (2023). Influence of Underlying Topography on Post-Monsoon Cyclonic Systems over the Indian Peninsula. Meteorology .
Phadtare, J. (2018). Role of Eastern Ghats Orography and Cold Pool in an Extreme Rainfall Event over Chennai on 1 December 2015. Mon. Wea. Rev. , 146 (4). pp. 943-965.
Organization and Life Cycle of Deep Cloud Systems in the Indian Summer Monsoon
Representation of clouds in the general circulation models is one of the biggest challenges for the atmospheric science community. Simultaneously resolving the full spectrum of the involved scales is computationally infeasible. Recent simulations from cloud-resolving models (CRMs) have shown promising results. However, the problem is not just limited to computational power; uncertainties plague our understanding of the physical processes in clouds. Therefore, there is a need to study real-world cloud processes and to set benchmarks for CRMs. High-resolution data from geostationary satellites is helpful for this purpose. During my PhD, I studied the life cycle of deep clouds of the Indian summer monsoon using INSAT-series satellite data. Special focus was on studying the cloud organization with and without the synoptic-scale forcing. An automated cloud tracking code was written for this purpose. Some of the questions addressed in this study are the following: Is there a systematic organization of MCSs within the monsoon depressions? In what aspects do the MCSs differ when the synoptic-scale forcing is strong and weak? Does the size spectrum of MCSs differ in different climatic conditions, e.g., ENSO?
Ref:
Phadtare, J., and Bhat, G.S., 2019. Characteristics of deep cloud systems under weak and strong synoptic forcing during the Indian summer monsoon season, Mon. Wea. Rev., 147(10), pp.3741-3758.