• D R Pattanaik

      Articles written in Journal of Earth System Science

    • Seasonal forecasting of tropical cyclogenesis over the North Indian Ocean

      D R Pattanaik M Mohapatra

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      Over the North Indian Ocean (NIO) and particularly over the Bay of Bengal (BoB), the post-monsoon season from October to December (OND) are known to produce tropical cyclones, which cause damage to life and property over India and many neighbouring countries. The variability of frequency of cyclonicdisturbances (CDs) during OND season is found to be associated with variability of previous large-scale features during monsoon season from June to September, which is used to develop seasonal forecast model of CDs frequency over the BoB and NIO based on principal component regression (PCR). Sixdynamical/thermodynamical parameters during previous June–August, viz., (i) sea surface temperature (SST) over the equatorial central Pacific, (ii) sea level pressure (SLP) over the southeastern equatorial Indian Ocean, (iii) meridional wind over the eastern equatorial Indian Ocean at 850 hPa, (iv) strength ofupper level easterly, (v) strength of monsoon westerly over North Indian Ocean at 850 hPa, and (vi) SST over the northwest Pacific having significant and stable relationship with CDs over BoB in subsequent OND season are used in PCR model for a training period of 40 years (1971–2010) and the latest four years (2011–2014) are used for validation. The PCR model indicates highly significant correlation coefficient of 0.77 (0.76) between forecast and observed frequency of CD over the BoB (NIO) for the whole period of 44 years and is associated with the root mean square error and mean absolute error ≤ 1 CD. With respect to the category forecast of CD frequency over BoB and NIO, the Hit score is found to be about 63% and the Relative Operating Curves (ROC) for above and below normal forecast is found to be having much better forecast skill than the climatology. The PCR model performs very well, particularly for the above and below normal CD year over the BoB and the NIO, during the test period from 2011 to 2014.

    • Easterly waves and ocean–atmospheric oscillations associated with contrasting northeast monsoon seasons over India

      R M REBA D R PATTANAIK P V S RAJU

      More Details Abstract Fulltext PDF

      The variability of synoptic conditions including the propagation of easterly waves (EWs) along with the ocean–atmospheric oscillations such as El Niño and the Indian Ocean dipole (IOD) associated with the large excess, large deficient and normal northeast monsoon (NEM) over the south peninsular India and particularly over Tamil Nadu (TN) met-subdivision during 2015, 2016 and 2017, respectively, have been investigated. It is seen that a strong El Niño and positive IOD exist during the excess NEM season of 2015 and was dominated by anomalous low-level easterly wind over the equatorial Indian Ocean (EIO), whereas, weak (strong) La Nina and negative IOD conditions prevailed during NEM 2016 (2017) was dominated with anomalous strong (weak) westerlies over EIO. Southward shifting of sub-tropical westerly jet (STWJ), presence of a secondary upper-level divergent outflow over eastern EIO and positive moisture convergence over the TN met subdivision are seasonal mean features observed during large excess NEM 2015. NEM 2016 (2017) is marked with absence of southward latitudinal shift of STWJ and negative (positive) moisture convergence over TN met-subdivision. Further, it is also seen that many active rainfall spells during NEM 2015 and 2017 over TN met-subdivision were associated with passage of EWs over the southern peninsula along east of 85°E, whereas, the large deficient NEM of 2016 witnessed no such active spell of monsoon and the passage of EW was confined to the eastern part of Bay of Bengal and never entered into the Indian peninsula.

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