Prof R R Kelkar’s book “Satellite Meteorology” Second Edition is now available.
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PROF. R. R. KELKAR'S BLOG ON WEATHER AND CLIMATE
February 15, 2017
June 6, 2014
Every year India has a date with the monsoon. The date is always 1 June, but the monsoon usually comes either earlier or later. This year it came on 6 June. Soon after IMD made the official announcement, PTI reported that “four days after missing its date with the country, the crucial south west monsoon has finally hit Kerala.” The onset of the monsoon was perhaps a hit-or-miss affair!
The India Today web site was charting the future course of the monsoon with great confidence. It said, “Monsoon arrives in Kerala, find out when it is reaching you.” It seemed to know the inner workings of the monsoon system more than anyone else!
Livemint.com held a negative view. It said that the progress northwards is expected to be slow and monsoon is unlikely to cover half the nation by the first half of June. Like the glass which can be half full or half empty!
The Wall Street Journal announced that the Monsoon had arrived over the Indian “mainland”, a word more familiar to Americans. It also quoted the Director General of IMD as saying that “the monsoon has finally arrived but it is currently moving at a slow pace as the parameters that support its progress are either weaker than their normal positions or not properly placed.” Whatever that may mean, WSJ hastened to add that “a weak monsoon could push up food prices and with it inflation, testing the new government’s ability to promote economic growth.”
The Hindu had mixed its metaphors quite thoroughly, reporting earlier in the day that the monsoon was about to make “landfall any time now”. Its special correspondent also added that the monsoon was “sailing in on weak tailwinds.” Is it a cyclone? Is it a plane? Is it a ship?
I had never imagined that the monsoon could be so vicious, but the Hindu also said that “the Andaman territory had come under the spell of the monsoon”.
The Free Press Journal, Mumbai, had a different story. “Monsoon set to catch up with city on June 10”, it announced. As if the city of Mumbai was moving northwards and the monsoon was racing it out with all speed.
And there was a man-made storm as well! On 4 June, Economic Times reported that “a storm is brewing over the onset of monsoon”! Not over the ocean as one may think, but with private forecaster Skymet declaring that it had spotted the monsoon and IMD maintaining that it had not!
The last word, however, was that of a Marathi news channel. It said that the Bay of Bengal had held the monsoon captive all these days, but finally the monsoon had managed to escape from its grip!
November 22, 2013
If winter comes, can spring be far behind? If Helen comes and goes, can Lehar be far behind?
On 22 November 2013, as cyclone Helen made landfall on the Indian coast, another storm was seen brewing in the southeastern corner of the Bay of Bengal (Satellite image source: IMD web site) If this system develops into a full-fledged cyclone, it would be named “Lehar” as per the naming system in vogue. It could take a long time for Lehar to reach the Indian coast, if it does indeed. In the mean time, the name reminds me of an old ghazal written by Mohammed Abdul Quadeer and sung by Ghulam Ali in 1981. Singing in his inimitable style, Ghulam Ali had told us how life is made worth living by breezes of freshness in the midst of turbulent waves.
Dil mein ek lehar si utthi hai abhi
Koi taaza hawa chali hai abhi…
Waqt accha bhi aaye ga
Gham na kar zindagi pari hai abhi
(There’s a wave rising in my heart
There’s a fresh breeze blowing now…
But good times will return, so don’t be sad,
There’s a whole life to live even now…)
As we watch cyclones come and go, we may as well spend some time listening to Ghulam Ali at
May 6, 2013
On 17 May 2013, the southwest monsoon set in over the Andaman Sea and parts of south Bay of Bengal.
Will the cylonic storm brewing over the Bay of Bengal pull up the monsoon or push it away?
The latest INSAT and Kalpana satellite images look beautiful! As if the monsoon is standing at the immigration counter with all valid documents in hand and seeking permission to enter India! Is it welcome or will it have to wait?
October 31, 2011
The Megha-Tropiques satellite has been lauched into an orbit that has a very low inclination of 20 degrees. It is not strictly an equatorial orbit but quite nearly so. The height of the satellite is 866 km and the swath or the north-south extent of the coverage is 1700-2200 km wide. The period of revolution is 102 minutes. The repetivity is 6 times a day over a large part of the tropical belt and 4-5 times a day at higher latitudes. The satellite has four payloads that would help estimate oceanic winds, rainfall, temperature and humidity profiles, total water vapour, cloud liquid water, cloud ice and several radiation budget parameters, all from a common platform.
Since 1982, the Indian Space Research Organisation has launched a series of geostationary satellites that have provided a continuous meteorological coverage of the Indian region and the surrounding land and Indian Ocean regions. Four satellites in the INSAT-1 series, three in the INSAT-2 series, the dedicated Kalpana-1 satellite, and the current INSAT-3A satellite, have carried a total of nine VHRR instruments so far, besides the CCD cameras on the more recent satellites. The next satellite, INSAT-3D, to be launched soon, will have an advanced 6-channel imager and a 19-channel sounder. However, these satellites have primarily been designed towards meeting the requirements of operational meteorology in India.
Megha-Tropiques is the first satellite of the Indian space programme that makes a welcome departure from this philosophy. It is going to make systematic observations of parameters related to climate studies and its sensor configuration is entirely different from the INSAT payloads. Geostationary satellites, because they have to be parked at a height of 36,000 km above the earth’s surface, are not suited for microwave remote sensing as the radiance reaching them is very weak. Megha-Tropiques being in a low altitude orbit is designed to make microwave measurements and it carries two microwave payloads.
Megha-Tropiques is a joint India-France (ISRO-CNES) mission with a shared responsibility for development of payloads as well as launch. The spacecraft was launched by ISRO with its Polar Satellite Launch Vehicle (Flight PSLV-C18) from Shriharikota on 12 October 2011. The expected mission life is 3 years.
The main scientific objectives of the Megha-Tropiques mission are:
(a) To collect a long-term set of measurements with a good sampling and coverage over tropical latitudes to understand better the processes related to tropical convective systems and their life cycle.
(b) To improve the determination of atmospheric energy and water budget in the tropical region on various time and space scales.
(c) To study tropical weather and climate events like monsoon variability, droughts, floods, and tropical cyclones, and their predictabilty.
Megha-Tropiques carries a rare combination of three state-of-art payloads, MADRAS, SAPHIR and ScaRaB designed for measurements of radiative fluxes, precipitation, humidity profiles and cloud properties.
MADRAS (Microwave Analysis and Detection of Rain and Atmospheric Structures), is a passive imaging radiometer operating at five frequencies of 18.7, 23.8, 36.5, 89 and 157 GHz in both H and V polarizations except the 23.8 GHz which has only V polarization. Data from the first three channels has applications in the retrieval of rain over oceanic regions, liquid water content in clouds and vertical integrated water vapour. Their spatial resolution is 40 km. The 89 GHz channel is useful for retrieving convective rainfall over both land and ocean at a resolution of less than 10 km. The 157 GHz channel is meant for measuring the concentration of ice particles in clouds at a resolution as high as 6 km.
SAPHIR (Sounder for Atmospheric Profiling of Humidity in the Inter-tropics by Radiometry) is a microwave sounding instrument. It has six channels in the frequency region of 183 GHz, all having 10 km ground resolution. SAPHIR data will be used to retrieve atmospheric humidity profiles at six levels up to a height of 12 km. After INSAT-3D is launched, SAPHIR soundings will complement the temperature and humidity profiles that will be derived from the INSAT-3D sounder.
ScaRaB (Scanner for Radiation Budget Measurement) is the third Megha-Tropiques payload. It has four channels: Sc1 – Visible (0.5-0.7 µ), Sc2 – Solar (0.2-4.0 µ), Sc3 – Total (0.2-100 µ), and Sc4 – IR Window (10.5-12.5 µ). Sc2 and Sc3 are the main channels of the ScaRaB instrument. ScaRaB will measure fluxes at the top of the atmosphere with a ground resolution of 40 km. Longwave irradiance can be calculated from the difference between Sc3 and Sc2 measurements. Images from Sc1 and Sc4 channels will be used for scene identification and will provide the necessary compatibility with operational satellites like INSAT which have radiometers with similar spectral channels.
The MADRAS payload has been developed jointly by ISRO and CNES France, while SAPHIR and ScaRaB have been developed by CNES. ROSA (GPS Radio Occultation Sensor) is another payload that Megha-Tropiques is flying. This has been procured by ISRO from Italy. ROSA operates at L1 and L2 frequencies of 1575.42 and 1227.60 MHz and will be used for retrieving temperature and humidity profiles in the atmosphere by the GPS occultation method.
India launched the Oceansat-2 satellite on 23 September 2009, which has an on-board Ku-band scatterometer for measurement of surface winds and is already providing useful data on the global oceans. The launch of INSAT-3D with its advanced imager and sounder, is now eagerly awaited. A synergistic utilization of the data gathered from all these satellites is certainly going to lead to a great advancement of the current knowledge of the role of the tropical atmosphere and oceans in the global weather and climate.
December 2, 2010
It is often said that weather does not respect political boundaries. Yet is it really so? Well, not always, I should say. In this post I present a selection of satellite pictures which show that cloud systems do tend to follow political boundaries.
In the satellite image below, the entire country of Sri Lanka is seen to be covered by cloud while the surrounding oceanic region and most of the Indian peninsula is cloudfree.
Similarly in the image below, we see the whole of Bangladesh covered by thick fog whereas West Bengal and the adjacent northeastern states of India have clear skies.
Here are two satellite images that show the state of Maharashtra to be free of any clouding while the four states of southern India are covered by clouds. The northern edge of the cloud cover closely follows the southern political boundary of Maharashtra, as if it is hesitant to cross over into the state!
The state of Orissa is seen in the picture below to have clouds confined within its territory while the surroundings states have quite clear skies.
India is divided into 36 meteorological subdivisions, like the state of Uttar Pradesh is divided into the meteorological subdivisions of East U. P. and West U. P. In this satellite picture we distinctly see East U. P. to be cloudy while the neighbouring West U. P. is not.
Fog naturally follows topographical features, and it is easy to spot fog over north India in satellite pictures by its northern boundary that follows the Himalayan foothills. But the southern boundary of widespread fog is seen in the image below to follow the southern boundary of the state of Bihar.
Again, in the fog situation seen below, the southern boundary of the fog matches the political boundaries of the states of U. P. and Haryana. It is also interesting that the fog boundary follows the India-Pakistan political border and Rajasthan is totally fog-free.
All the images in this post have been taken from the IMD web site http://imd.gov.in. I have mentioned the dates and times of the Kalpana-1 images, so that readers can draw their own conclusion as to the situations being just a matter of chance or that the weather does indeed follow geopolitical boundaries!