Role of moored buoy data in wave Role of moored buoy data in wave modelling for the north Indian Oceanmodelling for the north Indian Ocean

P Vethamony, K Sudheesh, Rupali P, MT Babu and P Vethamony, K Sudheesh, Rupali P, MT Babu and S JayakumarS Jayakumar

National Institute of Oceanography, GoaNational Institute of Oceanography, Goa

Usefulness of winds and waves:

• operations of drilling for the exploitation of natural resources in the deep sea

• ship - routing

• design of harbours, breakwaters and jetties

• loading and unloading of products from the vessels

• preparation of wind and wave atlas

• estimation of sediment transport and modelling of circulation, wave, oil spill and pollution.

In the present study:

• NCMRWF analysed winds are used as input to the model

• Bathymetry data are provided at grid points

• A few case studies have been carried out to test the accuracy of NCMRWF analysed winds and compared them with wind data from buoys

• Model gives wave statistics - height, period and direction of seas and swells, and, (ii) wave directional spectra.

• Grid data very close to the buoy location and ±0.5 h temporal variation are selected for comparison.

• The data of moored buoys are compared with the model output and altimeters (TOPEX).

Wave data from data buoys

- point measurements

- wave - height, period and direction are obtained continuously/ at fixed intervals

- accurate data compared to other sources

- data can be stored as well as telemetered

- expensive and maintenance & logistics problem

MIKE 21 OSW and NSW:

- OSW is a deep water wave model

- NSW is a nearshore wave model

- Output of OSW is used in NSW to get shallow water wave characteristics

- NSW considers refraction, shoaling, wave - current interaction and bottom dissipation

- Fine grid can be provided to NSW

- solves the energy balance equation for 2-dimensional wave spectrum

The model domain

• Bounded by 5 °S to 25 °N and 45 °E to 100 °E

• Objective analysis is used to convert the available NCMRWF winds (1.5X1.5 grid size for every 6 h interval in the form of U and V components)• Wave parameters are generated for 1h interval, but we have analysed 3h output.

Details of buoy data used for comparison

Buoy IDBuoy ID

Buoy positionBuoy position

RegionRegionLatLat LongLong

Deep water buoysDeep water buoys

DS1DS1 15153030 69691717 off Goaoff Goa

DS2DS2 10103737 72723030 off Lakshadweepoff Lakshadweep

DS3DS3 12123030 87873030 off Chennaioff Chennai

DS4DS4 18180000 88880000 off Paradipoff Paradip

Shallow water buoysShallow water buoys

SW1SW1 20°53’20°53’ 71°30’71°30’ Gulf of KhambhatGulf of Khambhat

SW3SW3 15°24’15°24’ 73°48’73°48’ off Goaoff Goa

SW4SW4 12°30’12°30’ 75°00’75°00’ off Kochioff Kochi

SW5SW5 08°42’08°42’ 78°21’78°21’ off Tuticorinoff Tuticorin

SW6SW6 12°30’12°30’ 77°30’77°30’ off Chennaioff Chennai

off Goa

off Kochi

Comparison between model and buoy significant wave heights (deep water): May – August 2000

off Goa

off Kochi

off Chennai

Comparison between model and buoy significant wave periods (deep water): May – August 2000

Comparison between model and buoy significant wave direction (deep water): May – August 2000

Off Goa

Off Kochi

Off Chennai

Correlation coefficients of SWH between model results and moored buoy data (May - Sep 2001)  

Buoy IDBuoy ID Model (MIKE21 OSW)

DS1 (off Goa) 0.910.91

DS2 (off Kochi) 0.890.89

DS3 (off Chennai) 0.680.68

SW1 (off Khambhat) 0.870.87

SW3 (off Goa) 0.880.88

SW4 (off Kochi) 0.930.93

• Validated model results can be used whenever it is difficult to make measurements

• Good match of model results with data buoy measurements have increased the reliability of model results

Scatter plot of wave heights (m) between MIKE 21(OSW)

and buoy May - Sept 2001

• Match between the altimeter • and measured data is very good

• Altimeter wave heights can substantiate measurements

• Match between the altimeter and modelled wave heights is very good

• Now, measured, modelled and altimeter data can compliment one another, wherever, data gaps are identified

Thank you