Significant increase in the frequency of occurrences of rainfall extremes has been reported over several parts of the world. These extreme events are usually defined at individual grids without considering their spatial extent. In this work, we show that the consideration of spatial collocation of extreme rainfall events while defining them gives a better understanding of the observed trends and underlying physical processes than using the traditional grid-based definition. The observed changes in the extreme rainfall events over central India after 1980 are mainly due to the changes in the average size of spatially collocated rainfall extremes and not due to the frequency of their occurrences (Fig. 1a). Based on the size, we classify extreme rainfall events into 3 different types viz., small, medium and large. Events of all sizes show a strong association with monsoon low-pressure systems (LPS) and occur mainly in the western sector of LPSs (Fig. 1 b). The large-scale background conditions, however, are different for different sizes of events (Fig. 1 c). For more details, check this work here .
In this work, we propose a mechanism for large-scale extreme rainfall events (area > 70,000 km²) of central India. The large-scale extreme rainfall events, though rare, have become more frequent recently. We show that these events occur when multiple monsoon low‐pressure systems are present at the same time. While the individual systems themselves need not be very strong, their simultaneous presence makes the environment conducive for sustained and organized deep convection, leading to large‐scale heavy rainfall events over central India. For more details, check this work here .
In this work, we examine under what conditions monsoon low-pressure systems give extreme rainfall events of different spatial extents viz., small, medium, and large over central India. The bigger size EREs (medium and large) are triggered by LPSs during the positive phase of the MISO. On the other hand, LPSs producing small events occur manily during the negative/neutral phase of the MISO. For more details, check this work here. You might a short video that covers this work useful.
I developed an alogorithm for the retrieval of cloud fraction and its classification for a ground-based sky imager as a master's project. It is based on RBR thresholding technique. This algorithm is currently used to process the images captured by a Total sky imager (TSI) at the Indian Institute of Tropical Meteorology, Pune . Details of this work can be found here .
Akshaya Nikumbh, A. Chakraborty, G. S. Bhat, D. M. W. Frierson "Multiscale interactions between monsoon intra-seasonal oscillations and low-pressure systems that produce heavy rainfall events of different spatial extents", Journal of Climate, September 2021. Link.
Akshaya Nikumbh, A. Chakraborty, G. S. Bhat, D. M. W. Frierson "Large-Scale Extreme Rainfall- Producing Synoptic Systems of the Indian Summer Monsoon." GRL, May 2020. Link
Akshaya Nikumbh, A. Chakraborty, G. S. Bhat, "Recent spatial aggregation tendency of rainfall extremes over India." Scientific Reports, June 2019. Link
Akshaya Nikumbh, B. PadmaKumari, Sneha Sunil, "Cloud Fraction Retrieval and its Variability during daytime from Ground-based Sky Imagery over a Tropical Station in India." Journal of Atmospheric and Solar-Terrestrial Physics, May 2019. Link
D. M. W. Frierson et. al., " Atmosphere and Ocean Energy Transport in Extreme Warming Scenarios", in prep.
Akshaya Nikumbh et. al., "Remote drivers of large-scale extreme rainfall events over central India", Under review.
Ms. Akshaya C. Nikumbh
Postdoctoral research associate
Atmospheric and Oceanic Sciences Program,
Forrestal Rd, Princeton, NJ 08540, United States.
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