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G. Ramachandran, K. V. Rao, and K. Krishna

Abstract

An observational study was undertaken at selected sites in and around a mountain gap to understand the downwind increase of winds transiting the gap. Observations indicate that there is a fanning out of surface winds emerging out of the gap. Computations show that downwind of the gap, there exist divergence in the lower levels and convergence upward of the level of maximum winds.

A model of the atmospheric circulation in the lower layers east of the mountain gap in question is suggested.

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G. S. Bhat, S. Gadgil, P. V. Hareesh Kumar, S. R. Kalsi, P. Madhusoodanan, V. S. N. Murty, C. V. K. Prasada Rao, V. Ramesh Babu, L. V. G. Rao, R. R. Rao, M. Ravichandran, K. G. Reddy, P. Sanjeeva Rao, D. Sengupta, D. R. Sikka, J. Swain, and P. N. Vinayachandran

The first observational experiment under the Indian Climate Research Programme, called the Bay of Bengal Monsoon Experiment (BOBMEX), was carried out during July–August 1999. BOBMEX was aimed at measurements of important variables of the atmosphere, ocean, and their interface to gain deeper insight into some of the processes that govern the variability of organized convection over the bay. Simultaneous time series observations were carried out in the northern and southern Bay of Bengal from ships and moored buoys. About 80 scientists from 15 different institutions in India collaborated during BOBMEX to make observations in most-hostile conditions of the raging monsoon. In this paper, the objectives and the design of BOBMEX are described and some initial results presented.

During the BOBMEX field phase there were several active spells of convection over the bay, separated by weak spells. Observation with high-resolution radiosondes, launched for the first time over the northern bay, showed that the magnitudes of the convective available potential energy (CAPE) and the convective inhibition energy were comparable to those for the atmosphere over the west Pacific warm pool. CAPE decreased by 2–3 kg−1 following convection, and recovered in a time period of 1–2 days. The surface wind speed was generally higher than 8 m s−1.

The thermohaline structure as well as its time evolution during the BOBMEX field phase were found to be different in the northern bay than in the southern bay. Over both the regions, the SST decreased during rain events and increased in cloud-free conditions. Over the season as a whole, the upper-layer salinity decreased for the north bay and increased for the south bay. The variation in SST during 1999 was found to be of smaller amplitude than in 1998. Further analysis of the surface fluxes and currents is expected to give insight into the nature of coupling.

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John E. Hart, G. V. Rao, Henry Van De Boogaard, John A. Young, and John Findlater

Abstract

This paper describes observation of the East African low-level jet stream obtained during June and July 1977 with a long-range research aircraft. We present results based on the real-time display of data on board the aircraft during the research flights. The jet stream core was located at about 40°E between 1 and 2 km altitude. The jet had a very sharp horizontal shear layer to the west of the core, with less pronounced shear to the east extending out over the ocean. Although flowing persistently from the south, it experienced a strong diurnal change over land. In addition, other changes in structure on a longer time scale were observed. This article presents the kinematic and thermal structure of the jet, and the low-level flow further upstream. Based on these data, the estimated cross-equational water vapor flux across the equator was found to be much higher than previously thought.

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Pankajakshan Thadathil, Prasad Thoppil, R. R. Rao, P. M. Muraleedharan, Y. K. Somayajulu, V. V. Gopalakrishna, Raghu Murtugudde, G. V. Reddy, and C. Revichandran

Abstract

The formation mechanisms of the barrier layer (BL) and its seasonal variability in the Arabian Sea (AS) are studied using a comprehensive dataset of temperature and salinity profiles from Argo and other archives for the AS. Relatively thick BL of 20–60 m with large spatial extent is found in the central-southwestern AS (CSWAS), the convergence zone of the monsoon wind, during the peak summer monsoon (July–August) and in the southeastern AS (SEAS) and northeastern AS (NEAS) during the winter (January–February). Although the BL in the SEAS has been reported before, the observed thick BL in the central-southwestern AS during the peak summer monsoon and in the northeastern AS during late winter are the new findings of this study. The seasonal variability of BL thickness (BLT) is closely related to the processes that occur during summer and winter monsoons. During both seasons, the Ekman processes and the distribution of low-salinity waters in the surface layer show a dominant influence on the observed BLT distributions. In addition, Kelvin and Rossby waves also modulate the observed BL thickness in the AS. The relatively low salinity surface water overlying the Arabian Sea high-salinity water (ASHSW) provides an ideal ground for strong haline stratification in the CSWAS (during summer monsoon) and in NEAS (during winter monsoon). During summer, northward advection of equatorial low-salinity water by the Somali Current and the offshore advection of low-salinity water from the upwelling region facilitate the salinity stratification that is necessary to develop the observed BL in the CSWAS. In the SEAS, during winter, the winter monsoon current (WMC) carries less saline water over relatively high salinity ambient water to form the observed BL there. The winter West India Coastal Current (WICC) transports the low-salinity water from the SEAS to the NEAS, where it lies over the subducted ASHSW leading to strong haline stratification. Ekman pumping together with the downwelling Kelvin wave in the NEAS deepen the thermocline to cause the observed thick BL in the NEAS.

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L. M. Bastiaans, D. R. Smith, R. A. McPherson, P. A. Phoebus, J. M. Moran, P. J. Croft, M. J. Ceritelli, G. V. Rao, J. T. Schaefer, F. J. Gadomski, K. A. Kloesel, R. G. Quayle, and J. W. Zeitler

The American Meteorological Society held its Sixth Symposium on Education in conjunction with the 77th Annual Meeting in Long Beach, California. The theme of the symposium was “Atmospheric and Oceanographic Education: Teaching about the Global Environment.” Thirty-eight oral presentations and 37 poster presentations summarized a variety of educational programs or examined educational issues for both the precollege and university levels. There was also a joint session with the Eighth Symposium on Global Change Studies and a special session on “home pages” to promote popular meteorological education. Over 200 people representing a wide spectrum of the Society attended one or more of the sessions in this two-day conference where they increased their awareness of teaching about the global environment.

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David R. Smith, Lisa M. Bastiaans, Jon W. Zeitler, Renee A. McPherson, Nezette N. Rydell, G.V. Rao, H. Patricia Warthan, Kevin A. KIoeseI, Brian E. Heckman, and Mohan K. Ramamurthy

The American Meteorological Society (AMS) held its Fifth Symposium on Education in conjunction with the 76th Annual Meeting in Atlanta, Georgia. The theme of this year's symposium was “Atmospheric and Oceanic Sciences: Building the Future on a Solid Foundation.” Thirty-four oral presentations and 41 poster presentations summarized a variety of educational programs or examined issues of importance for both the precollege and university levels. There was also a joint session with the 12th International Conference on Interactive Information and Processing Systems for Meteorology, Oceanography, and Hydrography on new technologies for the classroom. Over 200 people representing a wide spectrum of the Society attended one or more of the sessions in this two-day conference, where they increased their awareness of educational initiatives of members and institutions associated with AMS.

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P. A. Francis, A. K. Jithin, J. B. Effy, A. Chatterjee, K. Chakraborty, A. Paul, B. Balaji, S. S. C. Shenoi, P. Biswamoy, A. Mukherjee, P. Singh, B. Deepsankar, S. Siva Reddy, P. N. Vinayachandran, M. S. Girish Kumar, T. V. S. Udaya Bhaskar, M. Ravichandran, A. S. Unnikrishnan, D. Shankar, A. Prakash, S. G. Aparna, R. Harikumar, K. Kaviyazhahu, K. Suprit, R. V. Shesu, N. Kiran Kumar, N. Srinivasa Rao, K. Annapurnaiah, R. Venkatesan, A. S. Rao, E. N. Rajagopal, V. S. Prasad, M. D. Gupta, T. M. Balakrishnan Nair, E. P. R. Rao, and B. V. Satyanarayana

Abstract

A good understanding of the general circulation features of the oceans, particularly of the coastal waters, and ability to predict the key oceanographic parameters with good accuracy and sufficient lead time are necessary for the safe conduct of maritime activities such as fishing, shipping, and offshore industries. Considering these requirements and buoyed by the advancements in the field of ocean modeling, data assimilation, and ocean observation networks along with the availability of the high-performance computational facility in India, Indian National Centre for Ocean Information Services has set up a “High-Resolution Operational Ocean Forecast and Reanalysis System” (HOOFS) with an aim to provide accurate ocean analysis and forecasts for the public, researchers, and other types of users like navigators and the Indian Coast Guard. Major components of HOOFS are (i) a suite of numerical ocean models configured for the Indian Ocean and the coastal waters using the Regional Ocean Modeling System (ROMS) for forecasting physical and biogeochemical state of the ocean and (ii) the data assimilation based on local ensemble transform Kalman filter that assimilates in situ and satellite observations in ROMS. Apart from the routine forecasts of key oceanographic parameters, a few important applications such as (i) Potential Fishing Zone forecasting system and (ii) Search and Rescue Aid Tool are also developed as part of the HOOFS project. The architecture of HOOFS, an account of the quality of ocean analysis and forecasts produced by it and important applications developed based on HOOFS are briefly discussed in this article.

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J.-P. Vernier, T. D. Fairlie, T. Deshler, M. Venkat Ratnam, H. Gadhavi, B. S. Kumar, M. Natarajan, A. K. Pandit, S. T. Akhil Raj, A. Hemanth Kumar, A. Jayaraman, A. K. Singh, N. Rastogi, P. R. Sinha, S. Kumar, S. Tiwari, T. Wegner, N. Baker, D. Vignelles, G. Stenchikov, I. Shevchenko, J. Smith, K. Bedka, A. Kesarkar, V. Singh, J. Bhate, V. Ravikiran, M. Durga Rao, S. Ravindrababu, A. Patel, H. Vernier, F. G. Wienhold, H. Liu, T. N. Knepp, L. Thomason, J. Crawford, L. Ziemba, J. Moore, S. Crumeyrolle, M. Williamson, G. Berthet, F. Jégou, and J.-B. Renard

Abstract

We describe and show results from a series of field campaigns that used balloonborne instruments launched from India and Saudi Arabia during the summers 2014–17 to study the nature, formation, and impacts of the Asian Tropopause Aerosol Layer (ATAL). The campaign goals were to i) characterize the optical, physical, and chemical properties of the ATAL; ii) assess its impacts on water vapor and ozone; and iii) understand the role of convection in its formation. To address these objectives, we launched 68 balloons from four locations, one in Saudi Arabia and three in India, with payload weights ranging from 1.5 to 50 kg. We measured meteorological parameters; ozone; water vapor; and aerosol backscatter, concentration, volatility, and composition in the upper troposphere and lower stratosphere (UTLS) region. We found peaks in aerosol concentrations of up to 25 cm–3 for radii > 94 nm, associated with a scattering ratio at 940 nm of ∼1.9 near the cold-point tropopause. During medium-duration balloon flights near the tropopause, we collected aerosols and found, after offline ion chromatography analysis, the dominant presence of nitrate ions with a concentration of about 100 ng m–3. Deep convection was found to influence aerosol loadings 1 km above the cold-point tropopause. The Balloon Measurements of the Asian Tropopause Aerosol Layer (BATAL) project will continue for the next 3–4 years, and the results gathered will be used to formulate a future National Aeronautics and Space Administration–Indian Space Research Organisation (NASA–ISRO) airborne campaign with NASA high-altitude aircraft.

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