Construction and Quality of Best Tracks Parameters for Study of Climate Change Impact on Tropical Cyclones over the North Indian Ocean during Satellite Era - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 6

satellites. The Satellite Division of IMD is estimating centre positions and
intensities of CDs by the Dvorak method. The technique is subjective and
imprecise as high degree of skill is required to recognize cloud patterns. During
night, intensity of the disturbance is not available for want of visible cloud
imagery limiting operational requirement of the technique. While the Dvorak
method is the most popular technique for analyzing TCs/CDs through infrared
and visible imagery, it has some known weakness and biases, especially for
weaker systems. These have been described recently by Knaff et al. (2010).
Since 1970s, when system is within radar range, radar observation along
with satellite, ship and coastal observations were used to estimate intensity.
Since 2000s, the microwave imageries, coastal automatic weather stations
(AWS) (Mohapatra et al., 2011), high wind speed recorders and buoys are in
use in addition to above for location and intensity estimation. There are cases
like meso-cyclone Ogni (28-30 October 2006), which could be detected only
with the radar and coastal observations (Hatwar et al., 2008) and satellite failed
to detect it.
Microwave imageries from NOAA series, Metop-A, DMSP satellites are
used to analyze the inner structure of tropical cyclones. Several authors (Veldon
and Smith, 1983) have shown a potential usefulness of microwave image
products for the detection of the TC centre. However, the use of microwave
data in this regard has imitation primarily because of the low spatial and temporal
resolution of the microwave products. Furthermore, these methods use a limited
number of channels, usually the 85.5 GHz channel which is sensitive to the ice
particles, but has a higher spatial resolution than lower frequency channels, for
the determination of TC centre. Recent development of the web based TC
information distribution system by Hawkins et al. (2001) shows many
advantages of microwave data over the current visible/IR data especially when
the TC is in the development stage. Velden et al. (1989) found an objective
way for centre determination of TCs using multispectral satellite imagery called
the Automated Rotational Centre Hurricane Eye Retrieved (ARCHER). The
algorithm finds the centre of rotation using spirally oriented brightness
temperature gradients along the ring-shaped edge of a possible eye.
Determination of the centre of a CD is important, as the intensity based on
Dvorak's technique depends on the location of convection with respect to centre
of the CD.
Several studies have been made to convert microwave-based brightness
temperature of the cloud into surface wind associated with TCs (Evans and
Stephans, 1993; Kummerow et al., 1996). The brightness temperature is used
to determine Estimated Central Pressure (ECP) and MSW of the storm
(Goodberlet et al., 1989; Bessho et al., 2006).
Currently, the intensity estimation takes into consideration (a) satellite
(INSAT/METSAT, NOAA, TRMM, SSMIS, scatterometer wind etc.), (b) radar
and (c) synoptic analysis. Like the location of the system, when the system is