港航外文翻译Word格式.docx

1、PGRemya, Raj Kumar, Sujit Basu and Abhijit SarkarOcean Science Division，Atmospheric and Oceanic Sciences Group,Space Applications Centre, Ahmedabad 380 015, India.Wave prediction and hindcast studies are important in ocean engineering, coastal infrastructure development and management.In view of spa

2、rse and infrequent in-situ observations, model derived hindcast wave data can be used for the assessment of wave climate in offshore and coastal areas.In the present study, MIKE 21 SW Model has been used to carry out wave hindcast experiments in the Indian Ocean.Model runs have been made for the yea

3、r 2005 using QuickSCAT scatterometer winds blended with ECMWF model winds. In order to study the impact of southern ocean swells, the model has been run in two different domains.The model simulated wave parameters have been validated by comparing with buoy and altimeter data and various statistical

4、yardsticks have been employed to quantify the validation. Possible reason for the poorer performance of the model in the Arabian Sea has also been pointed out.1. IntroductionOcean wave hindcast and forecast are of paramount importance for the management of offshore structure construction, ship navig

5、ation, and naval operations. In-situ observations are location-specific and generally sparse. In the Indian Ocean the situation is worse, compared to the Atlantic and Pacific, because long time series data of in-situ observations are mostly unavailable. On the other hand, it is simply impossible to

6、estimate the wave climate and extreme sea state without such a long time series. Hence, in recent years, the attention is shifted to the use of numerical wave model generated wave data for the assessment of wave climate. Sverdrup and Munk （1947） were the first to develop operational wave prediction

7、technique. The technique was purely statistical and was based on just one parameter, viz., the significant wave height. In other words, the spectral character of the sea state was completely neglected.Later, the spectral characteristics of waves were taken into account for the development of methods

8、 based on wave spectrum. Currently, there are many spectral wave models for wave hindcast and forecast studies in the open ocean as well as in the coastal ocean. In the present study,MIKE 21 SW model has been utilized primarily for hindcast experiments. MIKE 21 SW is a new generation spectral wind w

9、ave model, based on unstructured meshes, and is developed by Danish Hydraulic Institute （DHI 2005）. The model simulates growth, decay, and transformation of wind generated waves and swells in offshore and coastal areas. As mentioned earlier, the principal objective of the present study is to carry o

10、ut hindcast experiments with MIKE-21 model in the Indian Ocean and to validate the hindcasts with available in-situ and remotely sensed data. As a spin off, we have also studied the impact of southern ocean wave conditions on the wave conditions of north Indian Ocean.Keywords.Wave modelling; MIKE 21

11、 SW; swell; altimeter.2. Data and methodologyMIKE 21 SW model is based on flexible mesh,which allows for coarse spatial resolution in the offshore area and high resolution in the shallow coastal waters. MIKE 21 SW model includes two different formulations: a directional decoupled parametric formulat

12、ion and a fully spectral formulation of the wave action balance equation. The first formulation is suitable only for near shore conditions, whereas the second one is applicable in both near shore and offshore regions. Hence, in this study the second formulation has been used as the study area contai

13、ns both shallow and offshore regions. In the fully spectral formulation the source functions are based on the WAM Cycle 4 formulation （Komenet al1994）. The source term for depth limited wave breaking is based on the formulation by Battjes and Janssen （1978）. A short description of the source term ca

14、n be found in Srensen et al（2004）. In the present study, the model domain covers the Indian Ocean region, 60S25N;40100E . For the model runs, the spatial resolution has been chosen to be 0.25in the coastal waters and 1for the rest of the region. This, however, does not mean that the resolution is co

15、nstant everywhere in this domain. MIKE 21 SW model uses a flexible mesh for model runs. The flexible mesh allows fine resolution near the coast. In fact, the resolution reaches as fine as 0.003near the coast in the flexible bathymetry grid used for this study. The bathymetry is from GEBCO （General B

16、athymetric Charts of the Ocean） produced by Intergovernmental Oceanographic Commission （2003）.The resolution of GEBCO bathymetry grid is 11minute. The model has been forced by QuickSCAT scatterometer winds blended with ECMWF model winds. The wind data are obtained from IFREMER, France, and are avail

17、able at a spatial resolution of 0.25in longitude and latitude. The quality of the blended winds has been checked by comparing them with buoy winds and the comparison has produced encouraging results. The wind speed correlation coefficients range from 0.80 to 0.90. The RMS difference between buoy win

18、ds and blended winds is2 m/s . The JASON 1 satellite system carrying a state-of-the-art altimeter sensor, launched on December 7, 2001, is providing wind and wave （besides sea level） information over global oceans regularly. 3. Model experimentsAs mentioned earlier, the basic objective is to carry o

19、ut hindcasts with MIKE-21 and subsequently to validate the hindcasts. For this purpose, the model has been earlier calibrated using number of in-situ data of Indian Ocean region and various model parameters such as breaking parameter, bottom friction and white capping were tuned to provide better wa

20、ve predictions.In the experiments,wave breaking parameter （= 0.5）, bottom friction （Nikuradse roughness） （KN= 0.04 m）, and white capping coefficients （Cdis=3.5） were found to be optimum. And these coefficients have been used in the experiments performed for the present study.However, in order to ful

21、fill the secondary objective of studying the impact of southern ocean waves on the northern ocean wave characteristics, apart from the earlier selected model domain, a smaller one （10S25N, 50100E） was also selected. Spatial resolution for the smaller domain （Domain 10S）model is identical with that f

22、or the larger domain（Domain 60S）. The model simulations were performed for the year 2005. The model derived wave parameters like significant wave height （Hs）, swell wave height （Hss）, wind sea height （Hsw）, mean wave period （Tm） and mean wave direction （MWD） were compared with similar parameters obt

23、ained from NIOT buoys, moored in the Arabian Sea （AS） and Bay of Bengal （BOB）. 4. Results and discussionsAs mentioned earlier, performance of the model was evaluated both in the larger and smaller domains. We evaluated the performance in terms of significant wave height, swell height, wind sea heigh

24、t, mean wave period, mean wave direction in both AS and BOB. In buoy measurements, for sea and swell separation, the wave spectrum measurements between 0.04 and 0.1 Hz is considered low frequency （swell） components and between 0.1 and 0.5 Hz is taken as high frequency （sea） components. Model also fo

25、llows the same criteria for the sea and swell separation. The definition of mean wave period from the buoy is . Although we compared the simulated and observed wave parameters at six different buoy locations for each of the basins, the results are shown at only one representative location for each o

26、f the basins. The Arabian Sea experiences three different seasons in a year: pre-monsoon （FebruaryMay）,southwest monsoon （JuneSeptember） and northeast monsoon （OctoberJanuary）. It can be seen that the deviation is more pronounced in premonsoon and northeast （NE） monsoon seasons.This finding was true

27、 for all the six buoys in the AS.During southwest （SW） monsoon season, the wind seas are dominating and this might be the reason for the change in performance during SW monsoon.During pre-monsoon season, large scale winds are weak and hence sea breeze has an impact on the diurnal cycle of the sea st

28、ate along the west coast of India. The study also clearly shows that MIKE 21 SW model is capable of providing good quality simulation of wind generated waves and swells in the offshore and coastal areas.5. SummaryIn this study, an attempt has been made to carry out hindcasts of wave parameters in th

29、e Indian Ocean using MIKE 21 SW model. Such hindcasts are important in ocean engineering and coastal infrastructure development and management. A variable resolution has been used for the proper representation of deep water waves and coastal waves. In order to evaluate the effect of southern ocean s

30、wells, two different model domains have been chosen. It has been found that there is indeed a significant impact of these swells on the model simulation in the Bay of Bengal basin. All the validation results point to the fact that the performance of the model is quite satisfactory. Hence it can be c

31、oncluded with reasonable confidence that the model with this particular configuration can serve the purpose of reliable wave hindcasts in the Indian Ocean region.ReferencesAboobacker V M, Vethamony P and Rashmi R 2011Shamal swells in the Arabian Sea and their influence along the west coast of India;

32、Geophys. Res. Lett.38（3）7p, doi: 10.1029/2010GL045736.Battjes J A and Janssen J P F M 1978 Energy loss and set-up due to wave breaking of random waves;Proc. 16th International Conference on Costal Engineering, ASCE,pp. 569587.Bentamy A, Ayina H L, Queffeulou P and Croize-Fillon D 2006 Improved near real time surface wind resolution over the Mediterranean Sea;Ocean Science Discussion3 435470.Bentamy A, Ayina H L, Queffeulou P, Croize-Fillon D and Kerbaol V 2007 Improved near real time surface wind resolution over the Mediterranean Sea;Oce