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B. K. MUKHERJEE
and
Bh. V. RAMANA MURTY

Abstract

Examination of the available rocketsonde data for the tropical station, Thumba, India, has shown that warmings, less pronounced than in the case of middle and high-latitude stations but of noticeable magnitude, and coolings of similar magnitude occurred in the mesopheric and upper stratospheric levels during the period, December 1970–March 1971. This was the only winter period when observations were made at the station during all of the 4 mo. No prominent change in wind has been observed in association with the warnings, however.

The maximum warming observed over a period of 1 week in the upper stratosphere was 26°C at 45 km. The upper mesosphere had been subjected to a continuous process of warming for over 3 weeks in December–January 1971 during which period the temperature rose by 48°C at 70 km. There is no definitive indication that these warmings were of the propagating type. However, they appear to have moved in the vertical at a rate of 3–5 km/day.

The temperature behavior of the lower stratosphere (50 mb) and the upper troposphere (300 mb) in the winter of 1970–71 was different than that which was observed in the preceding 2 winters.

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B. K. Mukherjee
,
K. S. Rao
, and
Bh V. Ramana Murty

Abstract

Computations of vertical motions in the middle atmosphere over the Indian tropical region have been made based on the thermodynamic equation with the geostrophic approximation. The authors have used the once weekly rocketsonde temperature and wind data for the tropical station Thumba India, (8°32′N, 76°52′E) for the four summers (1972, 1973, 1975 and 1976) and two winters (1971 and 1972) which are also years of varying monsoon activity.

In the tropical middle atmosphere, downward motion (subsidence) is the dominant feature when the motion field is considered in a longer time scale. The trend of fluctuations in vertical motion suggests wave structures in the tropical middle atmosphere. The magnitude of the extreme values of the vertical motion in the stratosphere over the high latitudes is larger, by a factor of 2 or more, than those obtained over the low latitudes (tropics). Whereas the magnitude of the vertical motion in high latitudes is associated with stratospheric warmings during winter, the values relating, to low latitudes are computed at 3 h intervals during March.

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B. K. Mukherjee
,
R. S. Reddy
, and
Bh V. Ramana Murty

Abstract

Temperature and wind data for the troposphere, stratosphere and mesosphere obtained from rocket-sonde/radiosonde/rawin observations made at a tropical station (Thumba, 8°32′15″N, 76°51′48″E) during five summer monsoons (1971–73, 1975–76) with differential monsoon activity were examined.

There is agreement between the occurrence of high-level warmings and monsoon activity in four out of five monsoons studied. There were no warmings in the year with very weak monsoon activity. The temperatures of the stratopause and the tropopause were significantly warmer in 1972 when the monsoon was very weak than in other years when the monsoon was active or very active.

There is a high positive correlation between the monsoonal activity (precipitation departure from normal over Indian subcontinent) and the 25 km mean zonal wind, and a strong negative correlation with the winds near 16 and 50 km. The change in the sign of correlation coefficient was due to the observed phase change with altitude of the quasi-biennial oscillation.

The study indicated the possibility of a relationship between stratospheric quasi-biennial structure and the Indian monsoon rainfall.

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R. S. Reddy
,
B. K. Mukherjee
,
K. Indira
, and
Bh V. Ramana Murty

Abstract

An investigation of the dates of occurrence of heaviest rainfall is very important for flood forecasting. We have considered this aspect in the present study by examining the daily rainfall data for four coastal stations Kakinada, Masulipatnam, Nellore and Visakhapatnam for the month of October for a 10-year period 1973–82. The data have been analyzed by considering the heaviest rainfalls for each station separately. We have defined the heaviest rainfall as that which exceeds two or more times the mean rainfall of the month. The study shows that heaviest rainfalls occur during the period 16–23 October. This feature is repeated year after year, constituting a rainfall singularity for the region.

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B. K. Mukherjee
,
K. Indira
,
R. S. Reddy
, and
Bh V. Ramana Murty

Abstract

In an earlier study a relationship was pointed out between phases of the quasi-biennial oscillation (QBO) in the lower stratospheric (30 mb) zonal wind and percentage departures of summer monsoon rainfall of India. That study was based on analysis of wind data for Thumba (8°32′N, 76°52′E) and the rainfall data for India for a short-period (1971–76). Wind data for Balboa (9°N, 80°W), which is also an equatorial station, and rainfall activity over India are now examined for a longer period (1951–82). About 15% of the variability in rainfall over India during the summer monsoon is associated with the pattern of the QBO.

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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
Full access
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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Qing Wang
,
Denny P. Alappattu
,
Stephanie Billingsley
,
Byron Blomquist
,
Robert J. Burkholder
,
Adam J. Christman
,
Edward D. Creegan
,
Tony de Paolo
,
Daniel P. Eleuterio
,
Harindra Joseph S. Fernando
,
Kyle B. Franklin
,
Andrey A. Grachev
,
Tracy Haack
,
Thomas R. Hanley
,
Christopher M. Hocut
,
Teddy R. Holt
,
Kate Horgan
,
Haflidi H. Jonsson
,
Robert A. Hale
,
John A. Kalogiros
,
Djamal Khelif
,
Laura S. Leo
,
Richard J. Lind
,
Iossif Lozovatsky
,
Jesus Planella-Morato
,
Swagato Mukherjee
,
Wendell A. Nuss
,
Jonathan Pozderac
,
L. Ted Rogers
,
Ivan Savelyev
,
Dana K. Savidge
,
R. Kipp Shearman
,
Lian Shen
,
Eric Terrill
,
A. Marcela Ulate
,
Qi Wang
,
R. Travis Wendt
,
Russell Wiss
,
Roy K. Woods
,
Luyao Xu
,
Ryan T. Yamaguchi
, and
Caglar Yardim

Abstract

The Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER) project aims to better quantify atmospheric effects on the propagation of radar and communication signals in the marine environment. Such effects are associated with vertical gradients of temperature and water vapor in the marine atmospheric surface layer (MASL) and in the capping inversion of the marine atmospheric boundary layer (MABL), as well as the horizontal variations of these vertical gradients. CASPER field measurements emphasized simultaneous characterization of electromagnetic (EM) wave propagation, the propagation environment, and the physical processes that gave rise to the measured refractivity conditions. CASPER modeling efforts utilized state-of-the-art large-eddy simulations (LESs) with a dynamically coupled MASL and phase-resolved ocean surface waves. CASPER-East was the first of two planned field campaigns, conducted in October and November 2015 offshore of Duck, North Carolina. This article highlights the scientific motivations and objectives of CASPER and provides an overview of the CASPER-East field campaign. The CASPER-East sampling strategy enabled us to obtain EM wave propagation loss as well as concurrent environmental refractive conditions along the propagation path. This article highlights the initial results from this sampling strategy showing the range-dependent propagation loss, the atmospheric and upper-oceanic variability along the propagation range, and the MASL thermodynamic profiles measured during CASPER-East.

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Andrey Y. Shcherbina
,
Miles A. Sundermeyer
,
Eric Kunze
,
Eric D’Asaro
,
Gualtiero Badin
,
Daniel Birch
,
Anne-Marie E. G. Brunner-Suzuki
,
Jörn Callies
,
Brandy T. Kuebel Cervantes
,
Mariona Claret
,
Brian Concannon
,
Jeffrey Early
,
Raffaele Ferrari
,
Louis Goodman
,
Ramsey R. Harcourt
,
Jody M. Klymak
,
Craig M. Lee
,
M.-Pascale Lelong
,
Murray D. Levine
,
Ren-Chieh Lien
,
Amala Mahadevan
,
James C. McWilliams
,
M. Jeroen Molemaker
,
Sonaljit Mukherjee
,
Jonathan D. Nash
,
Tamay Özgökmen
,
Stephen D. Pierce
,
Sanjiv Ramachandran
,
Roger M. Samelson
,
Thomas B. Sanford
,
R. Kipp Shearman
,
Eric D. Skyllingstad
,
K. Shafer Smith
,
Amit Tandon
,
John R. Taylor
,
Eugene A. Terray
,
Leif N. Thomas
, and
James R. Ledwell

Abstract

Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1–10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m2 s–1 as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level.

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