K. Revathy

Short-Period Features of the Interplanetary Plasma and Their Evolution

The solar wind plasma exhibits many features of the solar surface passed on to the interplanetary medium as temporal variations due to the solar rotation. The yearly average values of solar wind velocity, and geomagnetic index Ap during 1965–1999 were found to exhibit long period evolution. They were found to peak around the declining phase of each solar cycle. While the solar wind velocity peaks around the second half of the declining phase, the IMF field strength increases around the first half of the declining phase of each solar cycle. The power spectrum of these parameters shows peaks around 37-day, 30-day, 27-day, 13.5-day, 9-day, and 7-day periods. The temporal evolution of the power spectrum of the solar wind plasma parameters and the geomagnetic activity index Ap are also studied in detail and presented with the help of contour graphs. These studies indicate that the strength of the quasi-periodicities in the interplanetary medium evolves with time.

Galaxy classification using fractal signature

Fractal geometry is becoming increasingly important in the study of image characteristics. For recognition of regions and objects in natural scenes, there is always a need for features that are invariant and they provide a good set of descriptive values for the region. There are many fractal features that can be generated from an image. In this paper, fractal signatures of nearby galaxies are studied with the aim of classifying them. The fractal signature over a range of scales proved to be an efficient feature set with good discriminating power. Classifiers were designed using nearest neighbour method and neural network technique. Using the nearest distance approach, classification rate was found to be 92%. By the neural network method it has been found to increase to 95%.

A study of equatorial wave characteristics using rockets, balloons, lidar and radar

Abstract A co-ordmated experimental campaign was conducted for 40 consecutive days from 21 February to 01 April 2000 using RH-200 rockets, balloons, Rayleigh lidar and MST radar, with the objective of delineating the equatorial waves and estimating momentum fluxes associated with them. Winds and temperatures in the troposphere, stratosphere and mesosphere over two low latitude stations Gadanki (13.5°N, 79.2°E) and SHAR (13.7°N, 80.2°E) were measured and were used for the study of equatorial waves and their interactions with the background mean flow in various atmospheric regions. The study shows the occurrence of a strong stratospheric cooling (∼25 K) anomaly along with a zonal wind anomaly and this low-latitude event appears to be linked to high-latitude stratospheric warming event and followed by subsequent generation of short period (∼5 days) oscillations lasting for a few cycles in the stratosphere. Slow and fast Kelvin waves and RG wave (∼-17-day and ∼7.2-day and ∼4.2-day periods respectively) have been identified. The mean flow acceleration produced by the divergence of the momentum flux due to the observed Kelvin waves in the 35–60 km height region were compared with the zonal flow accelerations computed from the observed zonal winds. Contribution by the slow and fast Kelvin waves was found to be only ∼25 % of the observed acceleration during the evolution of the westerly phase of the semi-annual oscillation.

IMAGE ZOOMING BY WAVELETS

Enlargement and reduction of images are often required in image processing. Popular methods for re-sizing are standard interpolation methods. Recently, wavelets and fractal-based methods are developed for re-sizing. In this paper, wavelet zooming algorithm based on pyramid algorithm for wavelet transformation is explained. Also performance analysis of wavelet-based zooming method is investigated. We find that wavelet zooming with enhanced coefficients gives better visual quality. The objective error analysis also agrees with this. Wavelet zooming has also been performed block-wise. A significant drawback of the method is that the scaling factor should be power of 2.

Fractal Analysis of Ionospheric Plasma Motion

The plasma motion in the ionospheric F region has been subjected to fractal analysis. The fractal dimension of the observed data was obtained by both Fourier and fractal methods. The computational complexity of the two methods has been compared. It is shown that the data processing task for a large amount of data can be characterized by using both the fractal and Fourier methods.