Interview with P.K. Das


Dr Taba recounts:

The first international conference in meteorology was held in 1853. Twenty years later the International Meteorological Organization (IMO) was created. That was a non-governmental body established to ensure continued progress in the science of meteorology and also to ensure that all nations could reap the practical benefits that such progress would make possible. Exactly 100 years later and in the same conference room in Vienna, the Organization which was to succeed IMO held a centenary celebration attended by 210 participants, including representatives of 73 countries and 17 international organizations. IMO served the cause of international meteorology well for almost three-quarters of a century and governments and meteorologists alike were, in general, well satisfied with such arrangements.

P.K. Das






P.K. Das

It became increasingly evident, however,  that such a status for the focal point of international meteorology was incompatible with the importance which meteorology was assuming in the context of the fast economic and technological developments being made. So, on 11 October 1947, the representatives of 31 countries signed a document which provided for the creation of a new governmental organization to be known as the World Meteorological Organization (WMO). The occasion was the 12th Conference of Directors of IMO in session at that time in Washington DC. The Conference had been convened in order to prepare the way for the transfer of IMO responsibilities to a new body more suited to meet the changing needs of the countries of the world. That document was the text of the WMO Convention. Further action was still needed to bring this agreement into effect and it was only on 23 March 1950 that WMO formally came into existence. A few years later, 23 March was declared World Meteorological Day—a day which has been celebrated each year since. In 1951, WMO began its activities as a governmental organization and a specialized agency of the United Nations. It took over the functions of IMO and accepted many additional responsibilities appropriate to its new status. In order to commemorate the IMO, the annual IMO Prize was established, to be awarded on an international basis to an outstanding meteorologist. In addition, it was decided to institute an IMO Lecture which would be delivered at each of the four-yearly sessions of the Congress of the Organization and would take the form of a review of progress in some branch of meteorology. An acknowledged expert in the chosen field would be invited to prepare the review which would then be published by the Organization. The actual lecture would be a condensed version of the review.

It goes without saying that considerable studies and consultations are required for choosing the most suitable expert to prepare the IMO Lectures.The first IMO Lecture was delivered at the Fifth Congress in 1967 with the title “The nature and theory of the general circulation of the atmosphere” by Prof. E. Lorenz1. The second IMO Lecture entitled “Radiation processes in the atmosphere” was given by Prof. K.Ya. Kondratyev2 in 1971. The Third Lecture, “The atmospheric boundary layer”, was given by Prof. R.W. Stewart in 1975. In 1979, Prof. B. Bolin3 presented the Fourth IMO Lecture “Climate changes and their effects on the hemisphere”. When it came to selecting an expert to prepare an IMO Lecture on monsoons, the name of Prof. P.K. Das was at the top of the list. Prof. P.K. Das is our interviewee in this issue.

The text of the Fifth IMO Lecture “Monsoons” was published by the WMO Secretariat in 1986. It describes the planetary aspects of monsoons, including its relation to the Inter-tropical Convergence Zone and discusses, inter alia, rainfall distribution, heat and moisture budgets and energetic aspects. It also explains different aspects of the monsoon in terms of instability, the conversion of available potential energy into kinetic energy and the distribution of kinetic energy from zonal motion to eddies; barotropic and baroclinic instability. In short, P.K. Das produced a valuable document, which will be extremely useful for many more years.

P.K. and Apanna Das


P.K. and Apanna Das

As I have already mentioned, World Meteorological Day is celebrated each year on 23 March. Each year, the Members of the Organization celebrate the Day around a central theme focusing on a specific aspect of meteorology.  The transfer of technology forms the basis of scientific, technical and operational activities in international cooperation in meteorology. Ways and mechanisms must be developed to promote the transfer of appropriate technologies to developing countries in order to bridge the gap in scientific knowledge and technical know-how. “Meteorology and the transfer of technology” was the theme selected for World Meteorological Day in 1993. The WMO Secretariat also publishes a booklet on the theme for which it seeks contributions from well-known scientists and experts in the field. For 1993, it was decided to seek the advice and collaboration of two experts, who would each bring a different yet valuable perspective to a controversial subject. The two most suitable, available persons were P.K. Das and F.M.G. Baker, former Executive Director of the International Council of Science (ICSU). The result is a booklet which is easy to read with abundant references and examples relevant to the meteorological community. I particularly like the opening lines:

Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime. Confucius, 500 bc.

P.K. Das is the winner of several awards, including a medal for his paper “Lee waves associated with large circular mountains” (Indian Journal of Meteorology and Geophysics); the K.R. Ramanathan Memorial Lecture (“Global warming”, 1990); the Datta Memorial Lecture Award (“Storm surges”, 1991); and the K.R. Ramanathan Medal, for contributions to monsoon dynamics and prediction of storm surges (1993). He is an elected fellow of the Indian Academy of Sciences (1975) and of the Indian National Science Academy (1981).

I have known Emeritus Professor P.K. Das for many years. We saw each other on numerous occasions, in Geneva, New Delhi and elsewhere and he was, without fail, calm, polite and helpful. He has been a good friend, a capable supervisor and an excellent professor to many. I was happy to see him once again for this interview.

I would like to thank Dr R.R. Kelkar, Director-General of the India Meteorological Department and Permanent Representative of India with WMO, for providing the facilities to conduct this interview. In the company of Dr Kelkar and Dr Das, I visited the Centre for Atmospheric Science in New Delhi, an impressive research institution which collaborates with 12 national and 14 international organizations. I had the pleasure of meeting many of the professors and research scientists working there, among whom I will mention here Ms Girija Jayaraman, Head of the Centre, and Profs S.K. Dube and U.C. Mohanty. I was briefed on the activities of the Centre which offers all sorts of opportunities for research work and studies in fields such as fluid dynamics, oceanography, tropical meteorology, air pollution, atmospheric chemistry and climate modelling.

This interview took place in New Delhi, India, in April 2002.

H.T. — Tell us about your parents, your primary and secondary schooling and the environment in which you grew up.

P.K.D. — I was born on 20 May 1926 at Madhubani, a small town in the northern part of Bihar, north-east India. Its capital is the city of Patna. The state is made up of fertile plains crossed by the river Ganga (previously known as Ganges). The main agricultural product of Bihar is rice, but the state is also rich in iron ore and coal. Bihar is a well known centre for Buddhist culture. The founder of Buddhism, Gautam Buddha, received his enlightenment by praying under a sacred tree in Bodh Gaya, which is a small town in the north. My late father was a member of the prestigious Indian Civil Service, whose members were selected after a stiff competitive examination in England. He was assigned to the Judicial Branch and rose to become a Judge of the Supreme Court of India. I am deeply indebted to him for providing me with an excellent education. In 1937, my parents sent me to the Doon School in Dehradun, a public school located in a city just south of the Himalayan mountain range. The school was founded by S.R. Das, a well-known philanthropist, and provided a very good all-round education. About 1940, a fierce cyclone devastated the town of Midnapore, a coastal city in the northern sector of the Bay of Bengal. I joined a party of students and teachers to do relief work there and saw for myself the terrible devastation a tropical cyclone brings.

H.T. — What about your college and university education?

P.K.D. — I joined the Science College at the University of Patna in 1944 and completed an honours degree in physics two years later. The courses stood me in good stead later. In particular, a text book entitled "Heat and Thermodynamics" by M.N. Saha, an eminent Indian physicist, turned out to be very useful for meteorology. Another book "The Upper Atmosphere" by S.K. Mitra, also an outstanding scientist, was very interesting. I joined the Department of Meteorology at the Imperial College of Science and Technology, University of London, in the autumn of 1946. This was a little over a year after the end of World War II and the living conditions in London were somewhat difficult. Sir David Brunt was head of the faculty. He was assisted by Prof. P.A. Sheppard and a few others. Sir John Mason4 and Prof. Eric Eady joined the faculty a little later. I did my thesis on cloud physics under Prof.

Reid Bryson, P.K. Das and N. Sen Roy

Aboard a US research aircraft, measuring the radiative balance over Rajasthan (from left to right): Reid Bryson, P.K. Das and N. Sen Roy

Sheppard, with emphasis on the computation of collection efficiencies of large raindrops falling through a population of small drops. Sir John Mason made a generous reference to this work in his book “The Physics of Clouds", which is now a classic. I enjoyed working with Prof. Sheppard, because he could explain his arguments well. My values of the collection efficiencies considered the radii of the small drops, which collide with a large drop, a feature that had been ignored in earlier work. An event of considerable interest was a lecture by the late Prof. Eady on the instability of baroclinic waves. He was able to show that the formation of a depression was similar to a process of natural selection amongst growing baroclinic waves riding on a much larger barotropic wave. This was a novel idea in those days and attracted much attention. Around this time, Prof. Jule Charney of the Massachusetts Institute of Technology (MIT) visited Imperial College and gave us a couple of lectures on his theory on wave dynamics. He and Prof. Eady had similar ideas and soon became good friends. My stay at Imperial College was made pleasant by the helpful attitude of the students and the members of the staff. Under the leadership of Sir David Brunt, it was a happy team.

H.T. — You then joined the Meteorological Department of India. What did you do?

P.K.D. — I joined the Department on 16 May 1949. I was one of the youngest to be selected for the Officer’s grade. My first posting was to Pune (formerly Poona), where the Department generously put me in charge of a new section “Investigation and Development” on weather forecasting. The first year was difficult because of the paucity of upper-air data. This made it extremely difficult to apply the techniques that I had learnt abroad. I tried drawing trajectories and streamlines on weather charts, and to delineate areas of wind convergence but the results were unsatisfactory. Similar difficulties were encountered when I tried to introduce constant pressure charts. Many  firmly believed in the existence of “fronts” in those days, but I could find little evidence to support them. In my spare time, I continued my earlier work on the collection efficiency of raindrops by considering a wider spectrum of drop sizes. My first paper on this subject was published in 1950. I also tried to understand in more detail the papers of Profs. Eady and Charney on the instability of baroclinic waves and the scale of atmospheric waves. Two of my senior colleagues, C.G. Pendse and K.N. Rao, helped me to clear my doubts. The former was a wrangler5 from Cambridge, and the latter was an eminent mathematician—we had many fruitful discussions. After five years in Pune, I was transferred to Guwahati, a station in the north-eastern state of Assam. I was assigned the task of raising the status of this station to a principal centre for aviation meteorology in north-east India. A meteorological radar was installed here during my tenure. I stayed for three years in Guwahati before another transfer to Delhi.

H.T. — You must have met many other distinguished scientists at that time during the course of your work?

P.K.D. — I was introduced to several senior colleagues who had achieved eminence. Prof. S.K. Banerji, the first Indian Director General of Meteorological Department, was a renowned seismologist. He was also the first to design a mathematical model for the impact of mountains on the summer monsoon winds. Prof. K.R. Ramanathan6 had retired but I got to know him later. He was an erudite scholar with noble ideals and he encouraged me in my research work. I received considerable help and advice from S. Basu and S.K. Pramanik. Mr Basu was Head of the Forecasting Division, an able synoptic meteorologist and a former student of Prof. M.N. Saha. Subsequently, Mr Basu became president of the WMO Commission for Synoptic Meteorology and, finally, the Director General of Meteorology in India. S.K. Pramanik was in charge of Climatology and Geophysics. He was a former student of Prof. Sydney Chapman in England and a pioneer in the study of atmospheric tides. P.R. Pisharoty and P. Koteswaram7 were good friends. The former had done pioneering work on the energetics of the atmosphere, while the latter’s main contributions were on jet streams.

H.T. — Tell us about your visit to MIT (1958-1960).

P.K.D. — During my stay in Delhi, I became interested in numerical weather prediction because it appeared to be the best way of changing meteorology into an engineering science. The Senior Officers of the Department were kind enough to depute me to MIT under a government fellowship. In my first year I did most of the graduate courses in meteorology and a few in applied mathematics. These included the courses of Prof. Jule Charney, Prof. Norman Phillips8 and Ed Lorenz, which were very good and provided me with a sound basis for further research. Around this time, Prof. Obasi, current Secretary-General of the World Meteorological Organization, also joined MIT. Towards the end of the first year at MIT, I became interested in a three-dimensional model designed by Norman Phillips, who had earlier designed the world’s first general circulation model. He was an excellent teacher. I wanted to modify his model into one which could simulate a steady monsoonal circulation over India. An interesting result that emerged was the requirement of a warming rate of about 3.2°C per day, over north-east India, and a cooling at the rate of 2.4°C per day over north-west India in order to maintain a steady monsoon. The full details were published in Tellus in 1963. The MIT authorities kindly provided me financial assistance to enable me to complete this research project. Another good friend of mine was Reginald Newell, a pioneer in assimilating data, both from the upper air and the oceans. I have derived much benefit from his publications.

H.T. — Tell us about your association with Reid Bryson and his team from the University of Wisconsin.

P.K.D. — After completion of my work at MIT, I submitted a thesis on this topic for a Ph.D. at the University of Calcutta, which I was awarded in 1963. The results were of considerable interest to Reid Bryson of the University of Wisconsin. In October 1966, he brought over a team of scientists to carry out aerial measurements by a radiometersonde over Rajasthan in western India. Surprisingly, his observations were fairly close to the cooling rates predicted by my steady-state monsoon model. The cooling was attributed to negative radiative forcing by dust particles over the arid regions of Rajasthan and western India. It is interesting to recall that the question of negative radiative forcing by dust is still a topic of some debate. Prof. Bryson kindly invited me to visit his university and deliver a lecture on the steady-state monsoon model. I visited Wisconsin in the late 1960s and had many useful discussions with the faculty and the research scholars. Stefan Hastenrath, whom I later met with in Africa and in India, became a good friend of mine. The trip to Wisconsin was an important stage in my career.

H.T. — How did you become involved in the WMO World Weather Watch and the Northern Hemisphere Analysis Centre?

P.K.D. — The World Weather Watch Programme was launched in 1963. Under its aegis, a Regional Meteorological Centre (RMC) was set up at the Meteorological Office in New Delhi. This was an extension of the Northern Hemisphere Analysis Centre (NHAC), which had been set up earlier there. Initially, the centre was combined with a centre for data exchange on a wider scale, so that the centre was known as the Northern Hemisphere Exchange and Analysis Centre (NHEAC), but this was later split into an analysis centre (NHAC) and  a centre for data exchange (NHEC). I was put in charge of the analysis centre, which became the RMC at New Delhi. I was keen to begin numerical weather prediction in India, but the absence of an electronic computer was a handicap. I tried to make up for this deficiency by trying a graphical technique that had been introduced by R. Fjørtoft9, but the results were still not satisfactory.

H.T. — When did you finally get an electronic computer?

P.K.D. — I had tried to run a few computer programs on a computer acquired by Prof. P.C. Mahalanobis for the Indian Statistical Institute in Calcutta and these programmes were useful for the initial stages of our work. Our first electronic computer was a second-generation IBM-360/44, which was installed at RMC/NHAC in New Delhi in 1973. Another computer, a generous gift from the Government of the Netherlands, was used for data exchange. The IBM-360/44 was a small machine by today’s standards, but it helped us overcome the earlier difficulties created by the paucity of data and to generate strong interest in numerical weather prediction in the Meteorological Department. I collected a band of young officers to help me with this, including H.S. Bedi, a very capable scientist, who left us after a few years, unfortunately, to join Florida State University. I wrote a paper with him on a model of the monsoon trough.

P.K. Das At a game park near Nairobi

At a game park near Nairobi

H.T. — You were transferred to Pune again.

P.K.D. — I received a promotion and was placed in charge of weather forecasting in Pune. This revived old memories of the early days, when I joined the Department as a weather forecaster. Three tropical cyclones struck the coasts of India and Bangladesh in quick succession in the 1970s. The most devastating one struck Chittagong, a major port in the southern part of Bangladesh, in 1970 and was reported to have caused 300 000 fatal casualties. The next one struck the port of Paradeep on the east coast of India in 1971 with  10 000 casualties. The third cyclone made landfall at Chirala, a small town in Andhra Pradesh on the Indian coast in 1977. It was estimated to have caused 20 000 casualties. These natural calamities led me to study the phenomenon of storm surges, because most of the casualties were due to an abnormal and sudden rise in sea- level. Alan Robinson from Harvard University was then on a short visit to India and showed keen interest in my work. At his suggestion, he and I sent short papers to “Nature”,  giving the results of our models. These publications generated a good deal of interest in India and abroad. I followed up that paper with a more detailed one in the Quarterly Journal of the Royal Meteorological Society, London. I am grateful to Brian Johns and the late Sir James Lighthill for many useful discussions on this topic. As an outcome of my work on this topic, I was invited by WMO to assist in preparing a manual on storm surges and spent a few months in Geneva. The publication was authored jointly by Drs Miyazaki from Japan, C. Jelesnianski from the USA  and me and was published as Marine Science Affairs Report No. 13 “Present Techniques of Tropical Storm Surge Prediction”, WMO-No. 500, in 1978. The late G.K. Weiss was of considerable help in preparing this publication. Although we had different views on some of the topics. he was generally constructive in his ideas.

H.T. — Tell us about your association with the Global Atmospheric Research Programme (GARP) and the Monsoon Experiment.

P.K.D. — In the mid-1970s, I was invited to be a member of the Joint Organizing Committee (JOC) of the GARP and got to know many of the top scientists in meteorology. I asked for a field experiment to study the summer and winter monsoons. This, I suggested, could be in the form of a subprogramme of GARP and, if possible, we could call it MONEX. There was considerable opposition to this proposal in the initial stages. Many felt that the available resources were limited and the main experiment, namely GARP, should receive top priority. However, after much effort, I was able to get the approval of the JOC for MONEX. This was an important milestone in my career.

International MONEX Management Centres (IMMC) were set up at Kuala Lumpur and New Delhi to supervise the winter and summer components of the experiment. A large number of scientists from different countries came to these centres to plan and implement the project. I was appointed by my Government to supervise the operations and WMO appointed R. Grossman from the USA to assist me. I also received much assistance from Bo Döös10 from the WMO Secretariat.


P.K. Das In Yerevan, Armenia






In Yerevan, Armenia, to attend a JOC meeting of GARP

He was a capable scientist with a flair for devising practical and feasible solutions to the many complicated problems that arise in a multinational project of this size. Time does not permit me to go into all the details of this unique experiment, but I should like to mention an interesting outcome of MONEX:  MONEX emphasized the importance of convection over the sea for generating the rain-bearing clouds over the Indian Ocean. This topic is currently being actively pursued with the use of weather satellites.

H.T. — You then became the Director General of Meteorology of India?

P.K.D. — The termination of MONEX led to a happy event. I was promoted to become the Director General of the Meteorological Department of India towards the end of 1979. This was the fulfilment of an ambition. Soon afterwards, I was elected to be a member of the Executive Committee of WMO by its Congress in 1979. The Congress also invited me to present the Fifth IMO Lecture at the following Congress in 1983 for which I chose the topic of monsoons. The full text of the lecture was published as WMO-No. 613. I am grateful to the scientific community for an enormous response to this monograph. Norman Phillips, my former teacher at MIT, read the monograph and wrote me a generous letter.

H.T. — When did you retire and what did you do?

P.K.D. — I was due to retire from the Meteorological Department of India in 1984 at the age of 58, when I received an offer from the WMO Secretariat to teach at the University of Nairobi in Kenya. After some hesitation, I decided to accept the offer as I had always enjoyed teaching assignments. I went to Nairobi early in 1983. This was my second visit to Africa, having had a short assignment of four months in Malawi in 1982 to assist the National Meteorological Service re-organize its forecasting services.

The University of Nairobi was a large organization. I taught dynamic meteorology at the undergraduate and graduate levels.


P.K. Das with R.R. Kelkar and H. Taba

New Delhi, April 2002 — P.K. Das with R.R. Kelkar, Permanent Representative of India with WMO (left), and H. Taba

The students were good and I enjoyed teaching them. I am greatly touched by the fact that whenever any of them visit India, they never fail to call on us at our house in New Delhi. Four graduate students were able to complete their Masters degree in the two years that I was with them—it used to take much longer. I tried to persuade Dr Nganga, the Head of the Department, to develop closer links with the port authorities at Mombassa, so that the courses in meteorology could also include some physical oceanography. This was important because the weather on the east coast of Africa is largely seasonal, like the summer and winter monsoons of India. In Kenya, they are known as the "long" and "short" rains and are closely linked to the seasonal movements of the ITCZ.

H.T. — When did you join the Centre for Atmospheric Sciences at the Indian Institute of Technology in New Delhi?

P.K.D. — Upon my return from Nairobi, I joined the Centre for Atmospheric Sciences (CAS) at the Indian Institute of Technology (IIT) in New Delhi. The Centre was established in 1979 and was sponsored jointly by the Ministry of Education and the Meteorological Department. The funds were released on a cost-sharing basis by the two agencies.

At that time, there were not many employment opportunities for experts in the atmospheric and oceanic sciences, despite the formation of an Institute for Medium Range Weather Forecasts around 1980 and an Indian Institute for Tropical Meteorology in 1960. I thought it would be a good idea to increase the number of avenues for research at other centres and  provided financial support, as far as possible, to a few other centres as well.

Over the four years (1985-1989) that I stayed at the CAS in New Delhi, I helped to train a number of young scientists on new techniques in dynamic meteorology and numerical weather prediction, especially on new models for the prediction of storm surges. Today, the Centre has 17 core faculty members and about 30 research scientists. They are engaged in developing various models in different disciplines. Recent additions to the work in progress at the Centre include models to simulate the dispersal of pollutants, changes in climate and the chemistry of aerosols.

The years I spent here, along with the earlier two years at Nairobi were happy, because I enjoyed teaching and being in the company of young scientists. Some of them have won awards and distinctions in the academic world. This is a source of great satisfaction to me.

H.T. — What did you do next?

P.K.D. — In 1989 I joined the Council of Scientific and Industrial Research (CSIR) as Scientist Emeritus. At this time, there was much debate on the rise in sea-level as a consequence of global warming. Like some other scientists, I had my doubts about the impact of global warming because of the many uncertainties. So I collected the tide-gauge records of all Indian coastal stations and carried out statistical tests to determine if indeed there was a rise in the observed sea-level. Not surprisingly, I found that some of the tide-gauge records indicated a fall—not a rise—in sea-level over the last decade. It seemed to me that the principal uncertainty lay in the changes brought about by tectonic movements on the seabed. I stayed at the CSIR until 1991.

H.T. — You also helped write the WMO booklet for World Meteorological Day 1993.

P.K.D. — WMO asked me to assist in writing a booklet on the transfer of technology in the context of global warming and a change in the climate scenario. I was happy to do so, but it was a difficult assignment because of the many divergent views. The booklet “Meteorology and the Transfer of Technology” was published in 1993 (WMO-No. 786). Despite the differences of opinion, the booklet provided some useful information.

H.T. — Do you feel satisfied with your professional achievements?

P.K.D. — Looking back over the years, I feel I have had a good career. Many able scientists have discussed problems of mutual interest with me and I have acquired a large number of friends, both in India and abroad. Their friendship will be a source of encouragement to me in the days that lie ahead.

H.T. — Dr Das, you are modesty personified. You have many friends all over the world and have yourself been a source of encouragement to many. Thank you for according me this interview.

  • 1 Interviewed WMO Bulletin 45 (2) [back]
  • 2 Interviewed WMO Bulletin 47 (1) [back]
  • 3 Interviewed WMO Bulletin 37 (4) [back]
  • 4 Interviewed WMO Bulletin 44 (4) [back]
  • 5 At Cambridge University (United Kingdom), a student placed in the first class of the mathematical tripos [back]
  • 6 Interviewed WMO Bulletin 32 (1) [back]
  • 7 Interviewed WMO Bulletin 39 (3) [back]
  • 8 Interviewed WMO Bulletin 44  (3) [back]
  • 9 Interviewed WMO Bulletin 37  (1) [back]
  • 10 Interviewed WMO Bulletin 46 (3) [back]


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