Birendra Kumar Nayak

Impacts of ENSO and IOD on tropical cyclone activity in the Bay of Bengal

Abstract The impacts of El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on tropical cyclone (TC) activity (intensity, frequency, genesis location, track and average lifetime) in the Bay of Bengal (BoB) are studied for the period 1891–2007 using cyclone e-Atlas of India Meteorological Department, Niño3.4 Index, Oceanic Niño Index and Dipole Mode Index (DMI). TCs in the present study include cyclones with maximum sustainable wind (MSW) ≥34 knots (referred as cyclonic storms) and severe cyclonic storms with MSW ≥48 knots. The study shows a total of 502 TCs over BoB during the 117-year study period at the rate of 4.29 TC per year. Seven-year running mean of TCs for the period 1891–2007 shows a decreasing trend. Correlation between Niño3.4 Index and DMI for the 117-year period is significant and positive and the significance level is higher (lower) for the period with higher (lower) TC frequencies. One-third monthly interval analysis for the 117-year period indicates first third (1–10) of November as the most favoured period of TC formation over BoB. 117-year study period is divided into years of ENSO (El Niño, La Niña and neutral ENSO) and IOD (+ve IOD, −ve IOD and no IOD) categories. Maximum frequency of TC is observed during La Niña years, −ve IOD years and also when La Niña co-occurred with −ve IOD. More severe cyclones are formed during La Niña and +ve IOD years. Genesis location of TCs indicates that during La Niña (El Niño) years, the TCs are oriented in the south-east–north-west (south-west–north-east) direction. TCs in no IOD and −ve (+ve) IOD years are more (less) in northern BoB (north of 15° N), while in southern BoB (south of 15° N), TCs are more (less) during no IOD and +ve (−ve) IOD condition. BoB is divided into four quadrants, and number of TCs in each quadrant is computed under different ENSO–IOD events. Peak direction of track movement is observed as north-east followed by north–north-west which is corroborated from the dissipation of TCs in the specific quadrant. Total TC tracks in the peak direction of track movement are maximum during El Niño and no IOD years. The study reveals that TCs with shorter lifetime are observed during El Niño and −ve IOD years, while TCs with longer lifetime are observed during La Niña, neutral ENSO and +ve IOD years. The decade with maximum TC formation is observed as 1921–1930, and the impacts of ENSO and IOD on decadal variability are distinctly observed.

Properties of Carry Value Transformation

Carry Value Transformation (CVT) is a model of discrete deterministic dynamical system. In the present study, it has been proved that (1) the sum of any two nonnegative integers is the same as the sum of their CVT and XOR values. (2) the number of iterations leading to either or does not exceed the maximum of the lengths of the two addenda expressed as binary strings. A similar process of addition of modified Carry Value Transformation (MCVT) and XOR requires a maximum of two iterations for MCVT to be zero. (3) an equivalence relation is shown to exist on which divides the CV table into disjoint equivalence classes.

Carry Value Transformation (CVT): It's Application in Fractal formation

In this paper the theory of Carry Value Transformation (CVT) is designed and developed on a pair of n-bit strings and is used to produce many interesting patterns. One of them is found to be a self-similar fractal whose dimension is same as the dimension of the Sierpinski triangle. Different construction procedures like L-system, Cellular Automata rule, Tilling for this fractal are obtained which signifies that like other tools CVT can also be used for the formation of self-similar fractals. Finally it is shown that CVT can also be used for the production of periodic as well as chaotic patterns.