Bernhard Haurwitz and James J. O’Brien
The scientific contributions of Abdul Jabbar Abdullah are in the field of dynamic meteorology, that branch of atmospheric science which aims at an understanding and an explanation of the behavior of our atmosphere by application of the laws of physics. In Abdullah’s research both his early training in mathematics at the American University of Beirut and his practical work as airport meteorologist in Bassrah, Iraq (1937-41), stood him in good stead, and his published papers show both his familiarity with the techniques of mathematical physics and his knowledge of the weather phenomena which he discussed.
One of his earliest scientific papers, his doctor's thesis  at M.I.T., dealt with the theory of atmospheric waves and constituted a thorough discussion of the energy propagation of such waves by means of their group velocity. He then directed his interest to the problem of the formation of cyclones of extra-tropical latitudes and investigated  the mechanical influence of a surge of cold air on cyclone formation. He showed that cold air pushing against less cold air will impart to this less cold air an amount of energy comparable to that found in a typical cyclone and compared his theoretical results with some cases of actual cyclones. It is remarkable, and quite characteristic also of Abdullah’s later work that he obtained good approximations to the real atmosphere with highly simplified mathematical models. In particular, he assumed that the atmosphere can be regarded as incompressible and that the decrease of the atmospheric density with height can be simulated simply by assuming a few homogeneous layers of different densities. This work is particularly important since it signaled the original application of the method of characteristics to meteorological problems. In just a few years, numerous other researchers followed Abdullah’s lead and applied this powerful tool for solving non-linear hyperbolic partial differential equations to atmospheric problems.
In the course of the mathematical analysis of the cyclone problem Abdullah also noted that the action of the cold on the less cold air may give rise at the upper boundary of the less cold air to what is known in hydrodynamics as a “solitary wave.” He conjectured that such phenomena may also exist in the atmosphere and investigated their atmospheric effects in two papers [17, 19]. From his studies he concluded that they may be identical with small migratory anticyclones identified by Fawbush and Miller in 1954 (Bull. Amer. Meteor. Soc., 35) in connection with tornado formations and called “bubbles” by them. These studies were in the forefront of another atmospheric specialty-mesometeorology. In the years to follow, mesometeorology blossomed into an important part of meteorology.
While solitary waves had heretofore been studied at the free surface of only one fluid layer, the solitary waves considered by Abdullah occur at an interface between two fluid layers of different density, a fluid model approximating the real atmosphere somewhat better. The investigation of these solitary interface waves suggested that they may under certain conditions trigger instability and even contribute to the formation of tornadoes.
A detailed study of the dynamics of fully developed tornadoes was undertaken by Abdullah in 1955  on the basis of a simple mathematical model consisting of a pure sink and a pure vortex in the hydrodynamic sense. As pointed out by Abdullah, such a mathematical model is highly simplified, since it neglects the effects of vertical motions, friction, and the latent heat of condensation in the outer region of the tornado. Nevertheless, Abdullah succeeded in accounting for the low central pressures and high velocities which produce the destructive effects of tornadoes. In another paper , eleven years later, Abdullah returned to the tornado problem and showed that the sound emission of tornadoes reported by many observers may be due to free vibrations of the tornado vortex provided that the vortex is sufficiently small, a conclusion which agrees with reports by observers that “musical” tones are only heard in connection with tornadoes of small diameter while only noise is heard from large vortices.
Abdullah also used similarly simple mathematical models to study the dynamics of larger atmospheric disturbances, namely tropical cyclones [11, 12, 14]. He was able to show that even with very simplifying assumptions, namely by replacing the compressible atmosphere by three horizontal layers with constant but different densities, by neglecting the effects of friction and of the Earth’s rotation on the atmospheric motions it is possible to account for the inner, calm or nearly calm zone, the so-called "eye of the storm” on purely hydrodynamic grounds. At the same time, he considered the possible vibrations superposed on a circular symmetrical hurricane and showed that those vibrations whose periods are longer than half the period of rotation of the storm core may lead to a band-like structure superposed on the circular symmetric motion. That such band-like structures exist in hurricanes has been well-documented by recent and numerous pictures of hurricanes from meteorological satellites.
Another problem to which Abdullah devoted much time and thought is that of the so called pressure jump lines [9, 15, 22]. According to observation the barometric pressure changes practically discontinuously along pressure jump lines, which are accompanied by locally severe weather disturbances such as squall lines. The hydrodynamic processes occurring on these lines and the mathematical methods for their study are very similar to those which Abdullah used in his studies of tornadoes and hurricanes.
It is perhaps one of the outstanding characteristics of Abdullah's research that in many instances he was able to explain theoretically many of the observed properties of the phenomena which he analyzed with the aid of highly idealized mathematical models. He was, of course, well aware that because of such simplifications his models could not tell the full story, but, on the other hand, the simplifications show in each instance for what facets of a particular atmospheric phenomenon additional factors have to be taken into account to achieve a full explanation.
A remarkable paper illustrating his ability to deduce the behavior of the atmosphere from a simple mathematical model is . He proposed a simple two-layer compressible atmosphere in which the lower layer has a constant lapse rate of temperature and the upper-layer is isothermal. His leading hypothesis is that cloud producing layers are caused by internal gravity waves. His model yields three levels in the lower layer within which clouds might be produced by internal gravity waves whose phase velocities are of the order of 10 m sec-1. These levels fall within the limits of observed altitudes of tropospheric clouds. At the same time, he found two levels in the isothermal upper layer which are suggestive of the position of the nacreous clouds in the lower stratosphere and of the noctilucent clouds near the mesopause,
As the appended list of publications shows, the preceding account deals only with a part of Abdullah’s work. His wide interests and his scientific abilities led him to make significant contributions to almost every phase of dynamic meteorology.
Most American scientists are familiar with his important contributions to Meteorology in the late 40's and early 50’s, first at Massachusetts Institute of Technology and then at New York University. And they have noted his numerous contributions in 1966 when he returned to the United States —first, as a Senior Scientist at the Advanced Study Program of the National Center for Atmospheric Research in Boulder, Colo., and, then, as a Professor of Atmospheric Sciences at the State University of New York at Albany. However, many U. S. scientists are unfamiliar with his dedicated teaching efforts in his home country of Iraq. From 1947-1962 Abdullah wrote or translated five physics and meteorology texts into Arabic for use at home. From 1959-1963, he served as the President of the young University of Baghdad. During his visits to the United States, his colleagues always were aware that he regarded Baghdad as home. Even the recent description of Abdullah in Men of Science listed home as Baghdad with office at NCAR, in Boulder, Colo.
Abdullah’s native country, Iraq, has lost one of its outstanding scientists. This loss is shared by the whole scientific community in which Abdullah has earned a prominent place through his work. Those of his colleagues who have had the good fortune to be personally associated with him professionally and as friends will remember him not only for his contributions to meteorology, but also for his fine human qualities.
- Group velocity of atmospheric waves. Sc.D. Thesis, submitted at M.I.T., 1946.
- Billow groups. Ann. of the N. Y. Acad, of Sci., 48, 1947, p. 744.
- Wave motion at the surface of a current which has an exponential distribution of vorticity. Ann. of the N. Y. Acad, of Sci., 49, 1949, p. 425.
- A problem in the rotation of fluids. Bull. Amer. Meteor. Soc., 28, 1947, p. 469 (Abstract).
- On the wave theory of cyclones. Bull. Amer. Meteor. Soc., 29, 1948, p. 284 (Abstract).
- Cyclogenesis by a purely mechanical process. J. Meteor., 6, p. 86, 1949.
- Effect of friction on atmospheric disturbances. Bull. Amer. Meteor. Soc., 30, 1949 (Abstract).
- The band-like structure of hurricanes. Bull. Amer. Meteor. Soc., 34, 1953, p. 86 (Abstract).
- A proposed mechanism of squall lines, the pressure jump line. J. Meteor., 10, 1953, p. 298.
- A note on the periodicity of some frontal precipitation. J. Meteor., 10, 1953, p. 228.
- The eye of the hurricane. N.Y.U. Meteor. Papers, 2, no. 2, Part I, 1953.
- The vibrations of a hurricane. N.Y.U. Meteor. Papers, 2, no. 2, Part II, 1953.
- A note on the tilted trough model. J. Meteor., 11, 1954, p. 249.
- A proposed mechanism for the development of the eye of a hurricane. J. Meteor., 11, 1954, p. 189.
- The meridional growth of a squall line. J. Meteor., 11, 1954, p. 301.
- Some aspects of the dynamics of tornadoes. Mon. Wea. Rev., 83, 1955, p. 83.
- The atmospheric solitary wave. Bull. Amer. Meteor. Soc., 36, p. 511, 1955.
- A severe duststorm in Iraq. Beit. z. Physik d. Atmosph., 29, 1956, p. 21.
- A note on the atmospheric solitary wave. J. Meteor., 13, 1956, p. 381.
- The rate of transport of mechanical energy by waves of the Westerlies. Proc. of the Iraqi Sc. Soc., No. 1, 1957.
- The atmospheric breakers, First Scientific Congress of the University of Baghdad, 1961.
- Head-on collision between two pressure jumps. J. Geo- phys. Res., 71, 1966, p. 1953.
- The musical sound emitted by a tornado. Mon. Wea. Rev., 94, 1966, p. 213.
- The spiral bands of a hurricane—a possible dynamic explanation. J. Atmos. Sci., 23, 1966, p. 367.
- A note on the square cloud. J. Atmos. Sci., 23, 1966, p. 495.
- The stratification of cloud layers in a stable atmosphere. Mon. Wea. Rev., 95, 1967, p. 189.
- Reply to Rodger A. Brown on . J. Atmos. Sci., 24, 1967, p. 305.
- Reply to Raymond Wexler on , J. Atmos. Sci., 24, 1967, p. 441.
- Internal gravity waves of finite amplitude in a stratified incompressible atmosphere, a quasi-characteristic method. NCAR Manuscript No. 218, 66 pp. plus 33 figs. (with J. O’Brien), 1966.
- The pre-warm front pressure jump (with J. O’Brien) (in preparation).
- The dynamic stability of a vortex-column; the tornado funnel. Structure and Modification of Clouds and Fogs, by Vonnegut, Blanchard and Cudney, Themis report, SUNY, January 1969, 33-49.
- A gravity wave of elevation overtaking a stationary warm front. Structure and Modification of Clouds and Fogs, by Vonnegut, Blanchard and Cudney, Themis report, SUNY, January 1969, 50- 52.