IAPRS & SIS, Vol.34, Part 7, "Resource and Environmental Monitoring", Hyderabad, India, 2002 
  
  
North Indian Ocean tropical cyclones develop in the Bay of 
Bengal and Arabian Sea during the srping and fall. Tropical 
Cyclones in this area form between latitudes 8°N and 15°N, 
except from June through September, when the little activity 
that does occur is confined to north of about 15?N. These 
storms are usually short-lived and weak; however winds of 130 
knots (150 mph) have been encountered. They often develop as 
perturbations along the Intertropical Convergence Zone 
(ITCZ); this inhibits summertime development since the ITCZ 
is usually over land during the monsoon season. However, it is 
sometimes displaced southward, and when this occurs, storms 
will form over the monsoon-flooded plains of Bengal. On the 
average, six cyclonic storms form each year. These include two 
storms that generate winds of 48 knots (55 mph) or greater. The 
Bay of Bengal is the area of highest incidence. However, it is 
not unusual for a storm to move across — southern India and 
reintensify in the Arabian Sea. This is particularly true during 
October--the month of highest frequency during the tropical 
cyclone season. It is also during this period toreential rains 
from these storms dumped over already rain-soaked areas cause 
disastrous floods. 
The Bay of Bengal is the breeding sea for tropical cyclones. 
The funnel shape whirlwind emerging in the Bay of Bengal 
generates cyclones and hit the coastal belts of India, 
Bangladesh and Myanmar. Most of the devastative cyclones in 
human history formed in this bay and the severest one was the 
Bakerganj cyclone, which battered the coast in the year 1876. 
April to May and October to mid December are the periods 
when westward propagating minor tropical disturbances near 
and over the South Andaman Sea and the South Bay of Bengal 
develop into cyclones. 
A favourable combination of meteorological forcing generated 
by tropical cyclones with some non-meteorological factors of 
the regions like very high astronomical tide, shallow bay, low 
flat terrain and funneling coastal configuration, generate huge 
storm tide over the coastal areas of the North Bay of Bengal. 
This may happen even in a storm of moderate intensity. A 
maximum storm tide height of 12.5 m was observed at 
Backarganj in 1876 cyclone. 
Presence of the ITCZ near the Equatorial region of the Bay 
of Bengal due to either advancement or retreat of monsoon 
(South west or North east) during these periods help to develop 
low level cyclogenesis into cyclone. Furthermore, presence of 
the sun over the region during the periods feeds the required 
sensible heat, the bay water maintains the critical ocean 
temperature of 26-27°C needed for cyclogenesis to sustain and 
intensify. As sensible heat maintains the vertical coupling 
between the lower and upper troposphere flow pattern in the 
cyclone, the absence of sensible heat leads to the degeneration 
of cyclone. Cumulus convection acts as prime mechanism for 
vertical coupling. Temperature below 26°C cannot contribute 
sufficient thermal buoyancy to sustain cumulonimbus 
convection. Cyclones are influenced, greatly, by the underlying 
ocean surface over which they form and travel. As long as 
cyclone remains over warm water, the energy is limitless. 
Warm and highly humid Equatorial and Maritime Tropical air 
spirals inward towards the centre of the low pressure to replace 
the heated and rapidly ascending air. Ascending air releases 
heat into the atmosphere cools and are condensed into cloud. 
Since tropical cyclones are warm core, air from the core rises 
up and cold air sinks down which converts heat energy to 
potential energy and, thereafter, potential energy to kinetic 
398 
energy. However, prime energy source in the storm field is the 
latent heat of condensation. 
As a consequence of the cyclone occurrences in the Bay of 
Bengal, huge loss of life (both human and cattle) has been 
occuring along with devastation of habitations and agriculture. 
The loss of human lives during some noteworthy cyclones 
occuring on the Orissa Coast in last about 70 years is as 
follows: Balaspre (1831) 22,000, False Point (1885) 5,000, 
Paradip (1971) 10,000, Super Cyclone (1999) 10000+. This 
will clearly indicate the enormity of the problem. Most of the 
lives are lost when the storm surge recedes and takes away 
every floatable material with it into the sea. For example, in 
last 30 years, nearly 9,00,000 people died due to disastrous 
cyclones in Bangladesh. 
The Cyclone induced SST cooling has been investigated by 
different authors, using remotely sensed data sets. The cooling 
of the sea surface induced by the tropical cyclone has air-sea 
parameter dependence i.e. storm strength, storm translation 
speed and upper ocean thermal structure (Suetsugu et al., 
2000). They have also concluded that the strong and slow 
moving typhoon causes the maximum cooling of 5°C in the 
rightward of the cyclone wake. A moving tropical cyclone 
produces a significant response in the ocean environment, 
especially in the thermal structure. Such a response has been 
identified in the open sea (Peter and shay 1995). Their result 
also shows that the sea surface cooling is biased towards the 
right of storm track and subsurface intense upwelling and 
cooling at the base of the mixed layer to the right of the storm 
track. When the storm moves rapidly, the maximum cooling 
occurs well to the right of the track, where as for slowly 
moving storms the maximum cooling occurs near or on the 
track (Stramma and Cornillon, 1986). 
In the present study we have made an attempt to investigate the 
Sea Surface Temperature cooling induced due to one of the 
most severe cyclones occurred in the Bay of Bengal during 
October, 1999 using the Sea Surface Temperatures derived 
from IRS-P4/MSMR and TMI data. 
The Indian "Super Cyclone" developed in the Bay of 
Bengal in October 1999 and became the strongest and 
deadliest cyclone in the region since the Bangladesh cyclone 
of April 1991. Some of the details of this cyclone and its 
effects are summarised below. 
An area of disturbed weather formed in the Gulf of Thailand on 
24 October 1999, moved northwestwards across the Malay 
Peninsula into the Andaman Sea on 25", intensified to a 
tropical storm and moves into the Bay of Bengal by 26 
October. This cyclone gained hurricane/typhoon strength 
(winds of 74 mph) during 27 October and Continued to move 
northwestwards towards India by 28" October. Its landfall 
over the Indian state of Orissa was on 29" October 1999. This 
cyclone started to weaken by October 30, 1999. 
The 1999 October third week cyclone ranks as one of the 
strongest recorded in this region, but as i