Indian Journal of Marine Sciences

(www. niscair.res.in )

[ISSN: 0379-5136      CODEN : IJMNBF ]

Total visitors: 2,623         since  18-03-08

 

VOLUME 37

NUMBER 1

MARCH 2008

 

CONTENTS

 

Special Issue

on

Antarctic and Southern Ocean – Physical Processes

 

 

Interannual variability of the South Indian Ocean in observations

        and a coupled model

        Bohua Huang & J. Shukla

13-34

 

 

Antarctica sea  ice variability and southeast Indian Ocean SST :  

        Possible relationship

        Shailendra Rai, N. Khare  & A. C. Pandey

35-39

 

 

Anomalous variation of sea surface height in Southwestern Indian 

      Ocean

      A. C. Pandey, Shailendra Rai & A. P. Mishra

40-46

 

 

QuikSCAT-based momentum flux analysis over the Southern Ocean

      Alvarinho J. Luis & Rasik  Ravindra

47-54

 

 

Sensitivity of the Indian Ocean circulation to surface wind stress

       A.C. Pandey  &  Shailendra Rai

55-61
 
 

Predictive skill of DEMETER models for wind prediction over southern 

      subtropical Indian Ocean   

      Shailendra Rai, A.C. Pandey, K.C. Tripathi & Suneet Dwivedi

62-69

 

 

Southern Indian Ocean SST indices as early predictors of Indian 

       summer monsoon

       K. C. Tripathi, Shailendra Rai, A. C. Pandey & I. M. L. Das

70-76

 

Simulation of Antarctic sea ice area with artificial neural network

     K C Tripathi & I. M. L. Das

77-85

 

 

 

In-situ data and NCEP reanalysis: A comparative study in the Southern 

      Ocean and Antarctic Ocean

      I. M. L. Das & Amitabh  Mitra

86-92

 

 

Meteorology of Southern Ocean in Lazarev Sea area as revealed from

      observations obtained from Indian Antarctic Expeditions

       R. P. Lal

93-98

 

 

Measurement of column ozone, water  vapour  over Indian Ocean

      S.L. Jain

99-103

 

 

Size distributions of aerosols over the Indian Ocean

      Vimlesh Pant, C.G. Deshpande & A.K. Kamra

 

104-108

  

Abstracts of the Papers

 

Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp. 13-34

 

Interannual variability of the South Indian Ocean in observations and
a coupled model

Bohua Huang* & J. Shukla

Department of Climate Dynamics, College of Science, George Mason University, Virginia, USA

Center for Ocean-Land-Atmosphere Studies, Institute of Global Environment and Society, Maryland, USA

*[E-mail: huangb@cola.iges.org ]

The mean state, annual cycle, and interannual variability of the coupled ocean-atmosphere in the South Indian Ocean produced by a 300-year simulation of a coupled ocean-atmosphere general circulation model (CGCM) are compared with those from 51-year (1950-2000) observational datasets. The CGCM simulates realistically the mean annual cycles for both the sea surface temperature (SST) and lower atmospheric circulation, including the seasonal positions of the 10oC and 20oC SST isotherms, the zonal and meridional migration of the South Indian Ocean subtropical high, and the fluctuation of the southeast trade winds and mid-latitude westerly winds.

Interannually, the dominant model anomalous SST pattern in austral summer and fall showed some similarities to the observed Indian Ocean subtropical dipole mode, featuring opposite SST anomalies between the northeastern ocean to the west of Australia and the southern ocean. The model pattern is different from the observed one in its overly zonal spatial structure. Both the model and observed anomalous events are generated in response to atmospheric perturbations over the subtropical and mid-latitude South Indian Ocean that disturb the subtropical high during austral spring and summer. The corresponding wind speed changes of the trade winds and westerly modulate the surface heat flux into the ocean and generate SST anomalies, which usually persist into austral fall and in turn modify the lower atmospheric circulation in the subtropical Indian Ocean, especially the areas near Madagascar in the fall season. In the observations, the initial extratropical atmospheric fluctuations are significantly correlated to the global tropical variations associated with El Niño/Southern Oscillation. They are more strongly linked to the southern annular mode in the model.

[Key words:   South Indian Ocean, air-sea interaction, interannual variability, coupled ocean-atmosphere general circulation                model]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.35-39

Antarctica sea ice variability and southeast Indian Ocean SST:
Possible relationship

Shailendra Rai1, N. Khare2 & A. C. Pandey1,*

1K. Banerjee Centre of Atmospheric and Ocean Studies, University of Allahabad, Allahabad – 211002, India

2National Centre of Antarctic and Ocean Research, Headland Sada, Vasco-da-Gama, Goa - 403804, India

*[E_mail: avinashcpandey@rediffmail.com ]

Relationships between the Antarctic sea ice variability and extrapolar climate variables especially the Indian Ocean SST have been explored and we have identified that the southeast Indian Ocean SST shows the most persistence relationship with Antarctic sea ice variability. The SST is the unique precursor for the Australian summer monsoon, Indian summer monsoon and ENSO phenomenon after the 1976-1977 regime shift and is also linked with recently discovered Indian Ocean Dipole event of subtropical Indian Ocean.

[Key words: Sea ice, southeast Indian Ocean, Antarctica, Southern Ocean, climate data, SST, sea ice edge]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp. 40-46

Anomalous variation of sea surface height in Southwestern Indian Ocean

A. C. Pandey*, Shailendra Rai & A. P. Mishra

K. Banerjee Centre of Atmospheric and Ocean Studies, University of Allahabad, Allahabad 211 002, India

*[E-mail: avinashcpandey@rediffmail.com ]

Model produced sea surface height anomalies (SSHA) are compared with Topex/Posiedon altimetry observation for the region 65° 15' S to 30° 45' S and 29° 15' E to 120° 45' E covering the Indian Ocean. Some resemblance was found between model and observation except for Agulhas return current system region. The interannual variability of the sea surface temperature anomaly (SSTA) and SSHA have been studied using 24 years model run data for the domain given above. This analysis demonstrates high correlation between SSTA and SSHA as evidenced by observational studies using altimetry data. Sea surface height variability in Southern Indian Ocean (SIO) is much higher compared to other parts of the Indian Ocean. Negative dipole mode event of Indian Ocean Dipole (IOD) was found in mode 2 of Empirical Orthogonal Function (EOF) analysis.

[Key words: Southern Indian Ocean, Indian Ocean sea surface height, sea surface temperature, Indian Ocean dipole]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.47-54

QuikSCAT-based momentum flux analysis over the Southern Ocean

Alvarinho J. Luis* & Rasik Ravindra

Polar Remote Sensing Division, National Centre for Antarctic and Ocean Research, Ministry of Earth Sciences,
Headland Sada, Goa 403804, India

 *[E-mail: alvluis@ncaor.org ]

Using QuikSCAT vector winds, the seasonal and interannual variability of momentum flux were studied to explore the underlining dynamics for its modulation over the Southern Ocean (SO) during August 1999 to July 2003. The wind speed validation of ship and QuikSCAT measurements in the western Indian sector of the SO showed a bias and root mean square error of 0.3 and 1.6 m/s, respectively. On seasonal time scales, the spatial wind stress patterns reveal a basin-wide variability and the boreal summer monsoon significantly influencing it in the Indian Ocean (IO) sector. The temporal march of the momentum flux for different ocean sectors exhibit a seasonal cycle with a maximum range between 0.13 and 0.18 N/m2 during August-September and a minimum range between 0.07 and 0.11 N/m2 during December – January, with a temporal shift of ±1 month between the sectors. The atmospheric pressure gradient between tropics and high latitudes enhances the momentum flux in the IO sector during austral winter. On interannual time scales the momentum flux maps indicate a marked regional variability which is highest in IO sector and an evolution of cyclonic circulation south of 50°S during austral winter. Based on earlier studies and after a detailed examination of SST and wind stress curl fields, it is argued that orientation of the SST gradient relative to direction of wind stress drive an atmospheric response through wind stress curl and divergence modulations, which in turn dictates the intensity of momentum flux on seasonal time scales.

[Key words: Southern Ocean, QuikSCAT vector winds, momentum flux, SST, Antarctic circumpolar current, wind stress curl, vector winds]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.55-61

Sensitivity of the Indian Ocean circulation to surface wind stress

A. C. Pandey* & Shailendra Rai

K. Banerjee Centre of Atmospheric and Ocean Studies, University of Allahabad, Allahabad 211 002, India

*[E-mail: avinashcpandey@rediffmail.com ]

There is a lot of debate on the responses of Antarctic Circumpolar Current (ACC) in relations to changes in Southern Hemisphere winds and how the momentum input by the surface wind stress can be transferred down to the ocean floor. An σ coordinate Ocean General Circulation model was used in the present study. The major circulations in the Southern as well as tropical Indian Ocean have been discussed. The sensitivity of model with respect to wind stress forcing has been performed by using the surface wind stress climatological data of Hellerman and daSilva for the Indian Ocean up to 60ºS. It has been found that the response of zonal wind stress over tropical Indian Ocean north of 5ºS was large. The response of change in surface wind stress was negligible in the Southern Indian Ocean.

[Key words: Southern Indian Ocean, circulation in Indian Ocean, wind stress forcing]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.62-69

Predictive skill of DEMETER models for wind prediction over southern subtropical Indian Ocean

Shailendra Rai, A C Pandey*,  K C Tripathi  &  Suneet Dwivedi

K. Banerjee Centre of Atmospheric and Ocean Studies, University of Allahabad, Allahabad – 211002, India

*[E-mail: avinashcapndey@rediffmail.com ]

The ensemble mean prediction of winds at 850 hPa from individual models of DEMETER project has been compared from NCEP observation over southern subtropical Indian Ocean during summer monsoon season (JJAS) for the time domain 1980-2001. Predictability of U850 hPa (U850) and V850 hPa (V850) has been tested by different statistical approach like root mean square error (RMSE) for the region between Madagascar and western Australia in view of the importance of this region in anomalous variation of south central African rainfall variability as evidenced by some recent studies. A dichotomous forecast skill measure has been performed by calculating predictive skill measures like accuracy, bias, probability of detection (POD), false alarm ration (FAR), probability of false detection (POFD), threat score (TS), equivalent threat score (ETS) and Heidke skill score (HSS) for model produced U850 and V850 from all the individual models and multi model ensemble (MME). It has been found that the root mean square error has been reduced by applying MME but there is no effect on dichotomous predictive skill measures.

[Key words: ECMWF, DEMETER Project, wind, Indian Ocean, forecast skill]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.70-76

Southern Indian Ocean SST indices as early predictors of Indian summer monsoon

K. C. Tripathi, Shailendra Rai, A. C. Pandey* & I. M. L. Das

K. Banerjee Centre of Atmospheric and Ocean Studies,
University of Allahabad, Allahabad - 211002, India

*[E-mail: avinashcpandey@rediffmail.com ]

Four indices of quarterly mean sea surface temperature (SST) values extracted for Southern Indian Ocean (SIO) region for which the maximum correlation with All India Rainfall Index (AIRI) was found with a lag up to 7 seasons w.r.t. the onset of monsoon. The Artificial Neural Network (ANN) technique has been used to study the predictability of the Indian summer monsoon with four indices individually as well as in various combinations. It has been found that two combinations of SST indices of SIO region, SIOI + ACCI and CSIOI + NWAI + SIOI + ACCI, show best predictive skill when used collectively. It has been found that the performance of the ANN model is better than the corresponding regression model in the prediction of ISMR indicating that the relationship between ISMR and SST indices are non-linear in nature.

           [Key words:   Artificial neural networks, error back propagation, monsoon, Southern Indian Ocean, sea surface temperature              indices, Indian summer monsoon, predictors]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.77-85

Simulation of Antarctic sea ice area with artificial neural network

K. C. Tripathi & I. M. L. Das*

K.Banerjee Center of Atmospheric & Ocean Studies, University of Allahabad, Allahabad – 211002, U. P., India

*[E-mail: drimldas@yahoo.com ]

The artificial neural network (ANN) has been used for simulation of Antarctic sea ice area anomalies. Various dominant cycles present in the data have been identified using the Fourier analysis. It has been found that the data of the Antarctic sea ice area has two dominant cycles: annual and half yearly. The effect of the presence and / or absence of these dominant cycles on the simulation results have been carried out. ANN can simulate the broad trend of the sea ice area anomalies when all the cycles are present. However, the prediction skill of model for intraseasonal variability degrades as we remove the trends. Further, the forecast have been verified on the basis of various attributes of the forecast.

[Keywords: Artificial neural network, Antarctic sea ice, Fourier analysis, activation function, sea ice, simulation, forecast, error back propagation]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.86-92

In-situ data and NCEP reanalysis: A comparative study in the Southern Ocean and Antarctic Ocean

I. M. L. Das* & Amitabh Mitra

K. Banerjee Centre of Atmospheric and Ocean Studies, University of Allahabad, Allahabad - 211002, India

*[E-mail: profimldas@yahoo.com ]

A special expedition was launched by the National Center for Antarctic and Ocean Research (NCAOR), India on board R/V Akademik Boris Petrov during 25 January to 1 April 2006 passing the Southern Ocean and reaching the Larsemann Hills area of East Antarctica. The surface layer in-situ data generated from the cruise are compared with that obtained from the NCEP reanalysis during the same period along the track of the vessel. It is concluded that the NCEP reanalysis sea surface temperature and air temperature have some discrepancies as the vessel enters the sea ice zone near the Antarctic coast. The air pressure is well modeled but the relative humidity shows high variability throughout the period of the study. The wind speed is poorly correlated with that obtained from the NCEP due to the use of “Course over the ground” in place of ship “heading” while calculating the true wind.

[Key words:   In-situ data, surface layer, NCEP reanalysis, Southern Ocean, Antarctic Ocean, sea level pressure, air            temperature, wind speed, relative humidity, SST]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.93-98

Meteorology of Southern Ocean in Lazarev Sea area as revealed from observations obtained from Indian Antarctic Expeditions

R. P. Lal*

India Meteorological Department, Mausam Bhawan, Lodhi Road, New Delhi – 110 003, India

*[E-mail:lalrp@yahoo.com ]

 

Ship observations taken during voyage through Southern Ocean and observations recorded at Indian Antarctic Station Dakshin Gangotri (DG), have been used to study the latitudinal and diurnal variations of air temperature and sea surface temperature (SST) and climatology of Lazarev Sea area. Air temperature and SST are highly correlated and the SST lags by
1.5 °C during summer and the degree of lag reduces as winter approaches. The meteorological surface observations show an annual mean surface pressure of about 985 hPa. Surface wind is mainly easterly with annual average mean wind speed of
17 Kn. The annual average air temperature is –16.6 °C with a highest average air temperature of –2.5 °C during January and lowest average air temperature of –28.1 °C during August. Highest maximum temperature of 9.9 °C and lowest minimum temperature of –52.0 °C has been reported from coastal station. Diurnal variations of SST and air temperature have been observed in Lazarev sea area. It was not feasible to visualize these variations on moving ship.

[Key words:   Southern Ocean, Lazarev Sea, latitudinal diurnal variation, diurnal variation, air temperature, SST, Dakshin Gangotri, meteorology, Antarctic expedition, wind field, atmospheric pressure, weather system]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.99-103

Measurement of column ozone, water vapour over Indian Ocean

S. L. Jain

Radio & Atmospheric Sciences Division,

National Physical Laboratory, CSIR, New Delhi-110012, India.

[E-Mail: sljain@nplindia.ernet.in ]

The study of various minor constituents in the atmosphere plays an important role in the understanding of physics, chemistry, dynamics and radiation budget of the atmosphere. These trace species have temporal as well as spatial variation and therefore the knowledge of latitudinal distribution of these species is of great significance. Keeping this in view a highly sophisticated and microprocessor based compact sun photometer consisting of five filter channels at 300, 305, 312, 940 and 1020 nm was used to measure column ozone, water vapour in addition to various other parameters such as UV-B radiation, near IR radiation, aerosol optical depth etc. The measurements were made from Goa, India (15° 24´ N, 73° 42´ E) to Maitri, Antarctica ( 70° 46´ S, 11° 45´ E) over Indian Ocean during 16th Indian Scientific Expedition to Antarctica
(December 1996-March 1997). It was found that water vapour decreased while total ozone increased as the ship moved towards the coldest, the windiest and the largest icy continent i.e. Antarctica.

[Key words: Column ozone, water vapour, aerosol optical depth, sun photometer, Maitri, Antarctica, Indian Ocean]

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Indian Journal of Marine Sciences

Vol. 37(1), March 2008, pp.104-108

Size distributions of aerosols over the Indian Ocean

Vimlesh Pant, C G Deshpande & A K Kamra*

Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, Pashan, Pune 411 008, India

*[E-mail: kamra@tropmet.res.in ]

Concentration and size distribution of aerosol particles in the size range of 0.5 to 20.0 µm were measured over the Indian Ocean during January 23 to March 31, 2004. Total aerosol concentration showed the North-to-South positive gradient with latitude over the Indian Ocean North of the Inter Tropical Convergence Zone (ITCZ). Minimum concentration of aerosols was observed immediately South of the ITCZ and it increased on either side of the ITCZ. Contrary to being monomodal in shape in this size range as is generally expected over open ocean, the aerosol size distributions followed the Junge’s power law and show the transport of aerosols from the Indian subcontinent to North of the ITCZ, even though several hundreds of kilometers away from the Indian coastline. Aerosols South of the ITCZ exhibited monomodal size distributions which were typical of marine aerosols in the pristine environments. Aerosol size distributions in the roaring forties clearly showed the generation of sea-salt particles due to the wave breaking activity in this region of high winds. Abundance of particles of  < 1.0 µm diameter dominated over the Indian Ocean North of the ITCZ.

[Key words: Aerosol size distribution, Indian Ocean, transport of aerosols, Southern Hemispheric aerosols]

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