Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 , 2
Open Access Discussions 100, 42 and 24 min ∼ , and B. Harmalkar 1 Ocean Science Ocean , T. M. Balakrishnan Nair 1 , S. Lobo 1 70 % of daily-mean sea-level variability ∼ , R. Luis 1 575 576 , K. Vijaykumar 1 57 % and ∼ , K. Sudheesh 1 , P. Vethamony 1 , K. Jyoti 1 , S. Mohan 1 This discussion paper is/has beenPlease under refer review to for the the corresponding journal final Ocean paper Science in (OS). OS if available. CSIR-National Institute of Oceanography (NIO),Indian Goa, National India Centre for Ocean Information Services (INCOIS), Hyderabad, Goa, India face, cause the seaand flooding surface of to the vast pile-up coastal on regions. Also, the the heavy coast rainfall and causes flooding leads of to river sudden inundation 1 Introduction Tropical cyclones (TC) are theintense most winds, destructive resulting weather in systemsand on high usually earth, surges, causing producing meteotsunami, damagethe torrential to Bay property rains, of severe and Bengal floods losscyclonic (BOB) of storms. and life. Intense the In Arabian winds north Sea associated Indian (AS) with Ocean, are TCs, both potential blowing genesis over regions a for large water sur- at Gopalpur, Gangavarm andshows Kakinada, that respectively. Multi-linear the regression localpressure) analysis surface is meteorological able to dataalong account (daily-mean the for east wind and and west coastsea atmospheric of level India. may The be remaining attributed part to of local variability coastal observed currents in and the remote forcing. these extreme events exhibitto strong 43 synoptic cm on disturbances the leadinggenerated west to sea coast level storm and oscillations 29 surge at cm theVerem up on measuring and the stations Karwar) east on and coast the east west ofenergy coast coast India bands (Ratnagiri, (Mandapam due centered and to at Tuticorin) E1tion periods of and of of India E2. 92, with E1 92.6, 43 significant 84.5on and and the 23 min. 74.8 east h The coast, at surge thecalm dome Ratnagiri, sea period has level except Verem oscillations for a and during more dura- Karwar, energy Thane respectively. bands were However, centred similar at to periods those of during The study examinesdepression the (Event-E1) observed in storm-generated thea Arabian sea-level Sea cyclonic variation from storm due 26 “THANE”ber to November–1 (Event-E2) December 2011. deep over 2011 The the and sea-level Bay and of surface Bengal meteorological during measurements 25–31 collected Decem- during Abstract Ocean Sci. Discuss., 11, 575–611, 2014 www.ocean-sci-discuss.net/11/575/2014/ doi:10.5194/osd-11-575-2014 © Author(s) 2014. CC Attribution 3.0 License. 1 2 Received: 13 December 2013 – Accepted: 27Correspondence January to: 2014 P. Mehra – ([email protected]) Published: 20 FebruaryPublished 2014 by Copernicus Publications on behalf of the European Geosciences Union. Coastal sea level response tocyclonic the forcing tropical in the north IndianP. Mehra Ocean Y. Agarvadekar 5 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent oceano- ff orts and in an integrated manner. ff Hz, which corresponds to a period of about 578 577 4 − ) by CSIR-NIO. This study is intended to investigate the sea http://inet.nio.org It is necessary that the problem of storm surge must be seriously addressed by the Apart from the studies carried out with a view to assessing the coastal vulnerabil- to days. For asurges is country of like great interest India,(ICON) and providing a it sea-level is and near surface required. real–time meteorological Anreal-time information integrated monitoring have over coastal internet been and observation in developed network near warning andIndia of established ( at storm select coastal & Island locations of contributing factor is wind actingproblem. over The the atmosphere forces shallow the water wateroscillation and body, which it of in is turn, water an respondsthe air-sea level by interaction generating storm with surges various are3 frequencies centred h and about (Platzman, 10 amplitudes. 1971). In In the the present spectrum, study our interest is confined to a few minutes of 20 cm during SW monsoon.data Antony at and Chennai, Unnikrishnan Visakhapatnam (2013) and used ParadipPoint, along hourly at the tide east gauge the coast head of IndiaRecently, of and Rao Bay at et Hiron of al. Bengal, (2013)India to simulated using analyse surges an statistically advance and 2-D the water depth-integrated levels tide-surge circulation along interaction. model the (ADCIRC-2DDI). eastcountries coast of of the various regionsStorm through surge collective is e generated partly by the atmospheric pressure variations, but the main induced surface cooling. Studying a of tide Tkalich gauge etSouth along al. China with (2013) Sea satellite is inlevel data, anomalies an Singapore revealed (SLAs) that important Strait at the factor (SS)positive hourly wind determining and us- to over of the monthly central the observed scales. order part variability Climatologically, of of SLAs 30 of cm in sea- during SS NE are monsoon, but negative, and of the order et al. (2012) reported the influence of upper-ocean stratification on tropical cyclone- cline of the deep array and at the onshore regions of the shallow array. In BOB, Neetu tions (June 2007 and(September November 2007), 2009) indicating similarities alongtuary in with of the the Goa sea-level Sumatra response in the inthe geophysical eastern the oceanographic tsunami Arabian Mandovi parameters Sea. es- due Wangan to et ocean al. the observing (2012) tropical reported system Cyclonenorthern the consisting Gonu, Arabian variations of Sea which in and a passed a deepinertial shallow over autonomous cabled oscillations mooring mooring system at system in all thecoincident in Sea moorings with the of from the Oman. Near- arrival thermoclinewere of to Gonu. recorded seafloor Sub-inertial were at oscillations observed the with to periods post-storm be of relaxation 2–10 stage days of Gonu, primarily in the thermo- graphic parameters in responsethe to response of tropical the cyclones.lagoon coastal Joseph regions to et of the al. easternlandfall tropical (2011) Arabian Sea at cyclonic examined (AS) the storm andsurements. northwest “Phyan”, Kavaratti Mehra Island during coast et 9–12 of al. November India, (2012) 2009 reported based until observed on storm-generated its in-situ sea-level and oscilla- satellite-derived mea- lect coastal regions such as Kochi2007), (Dinesh Odisha Kumar, 2006), state Mangalore (Kumar (Hegde etKaikhali and Raju, al., (Bhattacharya 2010), and Guleria, Cuddalore 2012). regionthe Bay Developments (Saxena of in et Bengal storm and al., the surge 2013)references Arabian prediction and Sea therein in have been (e.g., highlighted Das, byJain Dube 1994; et et Chittibabu al., al. (2009) 2007; et and and al., Rao 2000, et 2002; al., 2008). Dubeity, et few al., studies 2006; concentrated on the variations in characteristics of di tion of individual cyclones andpreviously associated by surges in several BOB investigators andal., (Murty AS 1999; have et Fritz been published al., etvulnerability al., 1986; assessment 2010; Dube and using et Joseph remotemodelling al., et and sensing 1997; al., GIS data, Sundar 2011). analysis; in et A these situ few studies studies observations, provided deal coastal numerical with vulnerability maps coastal for se- deltas in combination with tides and surges. A number of general reviews and descrip- and methodology, Sect. 3 presentsconclusions. our findings and discussions, and Sect. 4 provides level variations at selectand locations meteorological in disturbances the that BOB occurred and in AS 2011. Section due 2 to introduces tropical the cyclones data (TCs) 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | http:// and . erent events are as ff http://weather.unisys.com/ www.imd.gov.in cients of regression are obtained for monthly 580 579 ffi 9 meteorological events in the year 2011, with ∼ cient of regression. The regression is performed ) component of winds and atmospheric pressure . Coe ffi V P A , (1) ∈ + and ) is the dependent variable and the independent variables P η A V , 3 B U + 3 are the coe V B ), alongshore ( 2 U B , which provide location and intensity of tropical cyclones at 6 h inter- + U 2 and http://www.usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/best_tracks 1 B , B 1, + B 0 Event 1 (E1): 26 November–1 Decemberthe 2011, Arabian occurrence Sea. of deep depression in Event 2 (E2): 25–31Bengal. December 2011, passage of Thane cyclone in the Bay of B ). – – A multi-linear regression model linking sea level and atmospheric parameters has Sea-level data is de-tided using TASK tidal analysis and prediction program (Bell The tropical cyclone track data are obtained from P = A 4 (5) such events occurredabout in these AS episodic meteorological (BOB) events as is shown taken in from Fig. 1. The data and information data to estimate the SLR.series The of monthly estimated estimated SLR SLR for the is duration merged of to September generate 2011 the to time January3 2012. Results and discussions 3.1 Cyclone overview The north Indian Ocean experienced η Where sea level residual ( are crossshore ( ( using daily-mean SLR, of SLR during theplying event the as method well suggestedthe as by spectrum that Rabinovich of (1997). of the The the(1 SLR data background September–20 during duration signal November) E1 for is 2011.(background) (background) estimating obtained is Similarly, is 25–31 by the from December ap- data 26 (1 September–10 November–1 duration December) December during 2011 respectively. thebeen event established. E2 The model can be described in general as: et al., 2000) tofiltered obtain using sea-level residual 5th (SLR). orderthan The 2 Butterworth 5 h min in filter sea-level order dataat to to is various remove distinguish high-pass locations. oscillations the The withfrom nature Matlab spectrum periods of with Hamming oscillations of greater window induced SLR of by 256 data data tropical points is cyclones and obtained 50 % using overlap. The “pwelch” spectrum function used time-series data at 5been (10) min designed interval and from developed the in RGThe the (AWS). Marine observed Both Instrumentation parameters the (Table Division, systems 1) CSIR-NIO, have andfollows: Goa. the periods covered for di as shown in Fig.(RG), 1. which Summary measures of sea-level,2008) observations is and is described given the in in evaluational. detail Table and (2013). 1. by comparative RG The Prabhudesai studies acquires Radarover et samples have 5 Gauge min al. been over is 30 (2006, reported s recordedlected by at window by 5 at Mehra min autonomous 1 et interval. min weatherature, The interval station surface air and (NIO-AWS). meteorological pressure the AWS variablesaveraged average and samples are and col- (wind, relative then air humidity) recorded temper- data at every every 10 s 10 min over interval. a In window the of present 10 study, min, we have In the present study, welogical report events at the various response coastal and of31 Island the January locations 2012. of sea-level Study India to encompasses from the two 1pression episodic episodic September in meteorological 2011 November meteoro- events: to 2011 (i) (E1) deep in de- AS and (ii) the tropical cyclone “Thane” (E2) in BOB 2 Data and methodology www.imd.gov.in hurricane/ vals. The storm translational speedin is the calculated JTWC using tropical the positions cyclone every best 6 track h data. reported 5 5 25 15 20 10 15 10 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 N ◦ E near 490 km 956 mb ◦ ∼ ∼ on 30 Novem- N, 76.5 1 ◦ − E, started moving Oman coast. Third ◦ respectively during ff 2 E with maximum sus- 6 m s ◦ ∼ 25 cm at all the three lo- N, 65 as shown in Fig. 2f. The ◦ ± 26.1, 21.57 and 25.79 cm 1 − ∼ E and moved north-westward N, 87.5 30 kts. The system then weak- ◦ ◦ ∼ 3.5 m s ∼ N, 88.5 E, which further intensified into a deep ◦ ◦ with wind speeds peaking up to 7.4, 9.6 and ect of the storm-induced sea surface temper- 582 581 ff 2 − as shown in Fig. 2d and ECP falling to N, 90.5 s 1 ◦ 2 − 119.45, 95.37 and 108.19 cm ∼ 1554 km. The variance of SLR observed during 29 Oc- 45 m s ∼ ∼ 25 kts, which weakened into a well marked pressure area ∼ E, and started moving west-northwards on 29 October 2011. ◦ . However, during the minimum ECP, the translation speed also on 29 November and again increased to 1 and then became steady at 1 − − 1 N, 62 E) between 16:00 and 17:00 UTC on 2 November 2011. The system − ◦ 1.73, 4.76 and 0.8 m ◦ ∼ 2 m s 6.5 m s 4 m s ∼ ∼ at Ratnagiri, Verem and Karwar respectively (Fig. 4a.2–c.2). At Karwar, the ∼ 998 mb (Fig. 2b). The average translational speed of this system remained 1 Oman coast. Second, a depression originating at 10 ∼ − ff 43 cm with SLR variance of ∼ Similarly, during the study period, three meteorological events occurred in BoB. First, In Arabian Sea, the first episodic meteorological event, a depression named “Keila” 4.3 m s respectively (Fig. 3) However,ber the 2011 deep (E1) was depressiondistance in which of the originated Verem near from on proximity(Fig. the 26 1). to depression E1 the Novem- was centre measurement ableto on to sites. inflict 28 For surges November, example, at 2011 the Ratnagiri,E1 was Verem (Fig. and 3a–c). Karwar The which SLR peakedgiri, surge up Verem dome and has Karwar a respectively. The durationwith local of SLR surface 92.6, are meteorological 84.5 shown conditions and in along variance Fig. 74.8 h was 4. at During Ratna- E1 (26 November to 1 December 2011), the wind cations. Kiela and the subsequent depressionable from to 29 generate October to noticeable 10 sea-levelmeasurement November variations, sites are probably from not the due cyclonic totrajectory tracks. large For of example, distance Kiela’s the of distance ECP the tober of is Verem to to 10 the November at Ratnagiri, Verem and Karwar is ature (SST), and reduces further stormthe intensification Tamil Nadu (Mei et coast al., just 2012). southcember Thane of crossed 2011 Cuddalore and between weakened 01:00and and into its 02:00 a UTC neighbourhood. of well 30 marked De- low pressure area3.2 over north Kerala Response of Sea level toThe depression sea-level in residuals the (SLR) at Arabian Ratnagiri,visual Sea Verem (2011) observation and of Karwar SLR are shown indicates in that Fig. it 3. is The normally within surface winds peaked up to (Fig. 2e). The cyclone trackspeed turned to of westwards on 29th,translation with speed an of average translational a stormmodulating the can strength exert of the significant negative control e on the intensity of storms by (Fig. 2). Thane intensified into a very severe cyclonic storm with maximum sustained a depression originated on 22tained September surface 2011 at winds 21.5 of over Jharkhand close to Jamshedpurveloped on on 23 19 September October 2011.depression 2011 Another with at depression maximum de- 20.5 sustained surfaceened winds of into aand low northeast pressure Bay of area Bengal.as Third over a cyclonic depression Myanmar system on named and 25 “Thane” adjoining initially December originated 2011 Bangladesh, at Mizoram 8.5 (ECP) steady to reduced to ber. The system weakened intoArabian a Sea. well marked low pressure area over the west central Sea o westwards on 6 Novembersurface 2011. winds reaching It up thenwell to turned marked 30 low kts. northward pressure System area with over weakenedone, the maximum on within west a central 10 sustained Arabian couple November Sea of 2011, o the weeks, into developed southern on a 26 tip November of 2011ber at Indian 2011 7.5 00:00 sub-continent UTC, and itface intensified moved winds as west-northwards. reaching a up By deep to 28 depression 30 kts with Novem- (Fig. maximum 2a) sustained and sur- the minimum estimated central pressure originated at 13 Keila intensified as aup cyclonic storm to with 30 kts. maximumand Keila sustained long. surface crossed 54.30 winds Oman reaching coastweakened by close 4 to November 2011 north into of a low Salalah pressure (near area over lat. the 17.10 west central Arabian 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2 and 2 10 cm at Gan- 2.7 mb 2 ∼ ∼ ± − s 3.6 mb 2 15 (10) cm in ) at Gopalpur ∼ 2 14.1, 10.3 and ∼ ± ∼ 253, 112 and 246 ∼ 62 % to 25 % (46.0 % ∼ ; the direction also fluc- 1 − and 11.72 cm 2 6 m s 13.76 and 10.27 m ∼ ∼ 24.3 (23.1) cm even during E1. The ∼ C at the three stations (Fig. 5a.5–c.5). ◦ erent sites, to the tropical cyclone Thane, ff 584 583 during E2. Minor dip in SLR C to 2.7 C, which is the case with relative humidity also ◦ 2 ◦ 9.0 ∼ ect of long waves generated by the forcing due to E1 in 2 h) using a 5th order Butterworth filter (Fig. 6). The am- ff ≤ 10 cm, and less than at sites north of Thane (Fig. 3i). The SLR ± , with corresponding wind variance of 1 − 6.0 mb during E1 at the three station. However, anomalous temperature vari- ∼ 14.0 m s ∼ response to the cyclone Yemyin (Phyan) which occurred in AS during 23–25 June 2007 generated by the longfrom waves entering the open through sea. the Inpass open order boundary filtered to (harbour (time understand entrance) the period plitude harbour of oscillations, the high SLRs frequency are(Fig. SLR high- 6a), oscillations in less response atopen to Verem ocean and E1 and at Karwar Ratnagiri (Fig. thereforeever, is does 6b the and not Verem station c). have is the Thein located a Karwar resonance cove in station features and Mandovi may is of experience estuarystudy located a resonance and at in with harbour. Ratnagiri Verem, meteorological How- Mehra disturbances. station In et is a al. located similar (2012) reported the SLR oscillations of 3.4 Harbour resonance Harbour oscillations (coastal seiches)type as of explained by seiche Rabinovich motionharbours) (2009) that and are are occur connected specific through in one partially or more enclosed openings to basins the sea. (bays, They fjords, are mainly inlets and gavaram and Kakinada respectivelyand (Fig. remained 5b.2 north-easterly and (Fig. c.2). 5c.2(Kakinada). The and The c.2 wind atmospheric and direction Table pressure 3) stabilised and (Fig. during is 5a.4–c.4) E2 devoid at of shows Gangavaram any a noticeableSimilarly, the variance fall anomalous during of variations E2 in temperature at duethe Gopalpur, to Gangavaram range E2 and is are Kakinada. narrowed not down observed, from Similarly, however a reduction in relative humidity rangeto is 13.6 observed %) from at Gopalpur and Gangavaram (Kakinada). locations with maximum windtuated speed during reaching up E2 to anddirection till remained 10 southerly January afterremained 2012 high 5 (Fig. from 5a.2 January 26 December and 2012to 2011 a.3, till and Table 4 3). maintained January During 2012. this The E2, wind the speed wind peaked up speed the three locations and very similarKakinada. meteorological At conditions Gopalpur, exist at the Gangavaram winds and were weak as compared to the other two southern variations are within variability at Mandapam andThane track Tuticorin (Fig. was 3d less andrical e), compared amplification probably of to due the to other open thespeeds ocean sites following are waves two less on as near reasons: they north the (i) propagate centralSLR northwards the of depression rise geomet- and point is (ii) and also wind increases seen towardslocal at the surface Mandapam(Tuticorin) periphery. by meteorological conditions alongscale with extent SLR of are E2 shown is in Fig. evident 5. in The wind large and atmospheric pressure measurements at all E2, which occurred in BOB areoscillations shown (listed) (variance) in of Fig. 3 27.4 (Table cm 3).(Fig. SLR and 5a.1) exhibits and maximum 26.5 cm Ganagvaram (Fig. (47.8to cm 5b.1) 32.9 respectively. cm, At with Kakinada, the a15.0 cm SLR variance peaked was of up 23.3 also cm and observed Karwar) at due the to E2 coastal (Fig. sites 3a–c). located However, at in the the Island AS station, Port (Ratnagiri, Blair, Verem the SLR ations due to E1 were8.3 not observed to (Fig. 3.0, 4a.5–c.5), 13.1 but to(range the 6.8 narrowing range narrowed and down down from 15.5 from to 62at Ratnagiri, 8.3 to Verem 40.4, and 65.4 Karwar, to refer Fig. 41.3 4a.6–c.6). and 64.83.3 to 33.8 %, Response respectively of Sea level toResponse meteorological of events sea-level on as the storm east surges coast at of di India magnitude, indicating the e the open ocean. Thedegrees wind with direction respect (Fig. toThe 4a.3–c.3) North atmospheric stabilised (Table pressure 2) to anomaly at (Fig.falls 4a.4–c.4) Ratnagiri, by shows Verem a and variance Karwar of respectively. wind energy is less compared to the other two sites, still the SLR peaks are of same 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) by the e 43 min (Mehra et al., 128, 98 and 17 min. At ∼ ∼ erent sampling durations of sea-level ff ) as the independent variable is performed P 100 (2) 586 585 A × 10 (5) cm as both the gauges are located in the ) components of winds and atmospheric pressure ∼ ± V erences at high frequencies as seen in Fig. 7, indicat- 4 cm at Port Blair. ff ) ∼ ± ε ), along-shore ( variance( U variance(measured SLR) − 1 = ) individually as independent variable to regress the SLR. This is would enable us e erent sites have significant di E2 event and background SLR spectra estimated at Gopalpur, Gangavaram, Kak- E1 event and background SLR spectra estimated at Karwar, Verem and Ratnagiri P ff A with cross-shore ( ( daily-averaged. Therefore, in this sectionis daily-averaged used data to series perform of multi-linear regression. SLR To and begin with, AWS linear regression is performed In order to improve(5 min) clarity and and atmospheric parameters to (10 make min) compatible, the sea-level di and AWS data are model. Var 3.5 Regression model Multi-linear regression analysis ofnents SLR (U, V) as and the atmosphericas dependent pressure explained ( variable in with Sect.is wind 2 assessed compo- (Eq. by looking 1). at How the well percentage the of sea model level describes variance the explained (Var sea level residual (time period > 41 min)(shorter is time-period) similar, oscillations but withresonance the time-period occurring in 41, energy the 37, isand harbour. 25 background enhanced At and show for Port 12 similar higher min,17 Blair, min. variability the suggesting frequencies The with background SLR SLR event spectra spectrum peaksther has of at higher noticeable both peaks event 160, at the frequencies 85, 41absence event are and 47, of merged 26 harbour 41, min with resonance and 26 fur- as the and Port background Blair spectra, station indicates provides the open ocean conditions. is higher compared toand the 18 background min, SLR however the spectra backgroundGangavaram with spectra station peaks shows the peaks phenomena at of at 213, harbourwhere 98, resonance it 67, is clearly is 41, visible 25 not (Fig.arriving 5b.1), the from surge the but open high ocean. At frequency Kakinada oscillations (Fig. triggered 8c) by the the spectra long for lower waves frequencies present in the background signal. The event spectral energy at Gangavaram (Fig. 8b) peaks at 106, 80, 60, 45, 36, 21 and 12 min. The spectral peak at 45 and 21 min are also background with some detectable peaksfrequencies are at merged 106, with 67, the background 44(lack spectra, and of indicating 21 open-ocean harbour min behaviour resonance). andinant The further spectral influence higher peaks of at E1(Fig. 106, is 7e) also 53, the visible 44, event at 2480, spectra Tuticorin and 42 with is 18 and dom- min intertwined 26 min. (Fig. with 7d). background However, spectra at with Mandapam peaksinada, at and 116, Port Blair(Fig. 8a) during at E2 Gopalpur are is intertwined shown with in the Fig. background spectra 8. with The some event detectable spectrum during E2 during E1 as shownground in spectra with Fig. peaks 7a. atevent 182, At spectrum 91, Verem 40 at the and Verem was 20 event min2007 energetic spectra as and during shown is Phyan, Yemyin, in September where intertwined Fig. Sumatra a 7b.2012). Tsunami, with However, distinguished the back- Similarly, peak the was observed event at spectrum during E1 (Fig. 7c) at Karwar is similar to the brief amplitude of 10 cmhigh is frequency observed SLR (Fig. variations 6d, are eharbour and (Fig. f). 6g At and Gangavaram h), (Kakinada) and the are indicated in Fig.di 7 (see Sect. 2ing for the influence the of method local used). topography.well The lifted The event above spectrum background that at spectra of Ratnagiri of background is with high major in peaks energy, at 127, 80, 47, 30, 26 and 14 min are up to 10 (5) cmthe during common E1 boundary (Fig. of 6d Palk Strait andlevel and e). gauge the Mandapam Gulf is sea-level of gauge located Mannar, isof whereas in located the SLR on the Tuticorin sea- at Gulf the of stationsSLR Mannar amplitude located due in (Fig. to BOB 1). E2 are The at also high Tuticorin, shown Mandapam frequency in is oscillations not Fig. observable 6. and The at high Gopalpur pass a filtered (9–12 November 2009). The high frequency SLR oscillations at Tuticorin (Mandapam) 5 5 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , e V V U , & 6 % and U ◦ U ∼ 27 − 15 cm) till , is less than ∼ ◦ ] together is e P ] together are 12 P A ) winds are ob- , A 13.6 % (Fig. 9a.2 V , ∼ − V ∼ V , ] together are used < 23 % (20 %) in Oc- , P U U A ∼ 45 % of the daily-mean , ∼ V ect. The cross-shore wind increased to 66.3 %, when , ff e U will decrease (increase) the 57.2 % (Table 4). The is low e ∼ V & U 44.1 % (Fig. 9c.2 and Table 5). 75 % for September–November 2011 ∼ . During E2, the estimated (measured) ∼ 1 will increase(decrease) the SLR (Fig. 9) − ) will tend to increase(decrease) the sea ) will tend to decrease(increase) the sea is V V V e 76 % is highest at Verem among the three could explain the SLR variability by an aver- increases to ( 70 %. In January 2012, the Var − & ] together are used as independent variables ( 588 587 ∼ P U will decrease(increase) the SLR (Fig. 10). ) at Gopalpur, which are seaward(southward) e ∼ P U U e 10 m s A − V A V − , ( & 50 % during October and December 2011 (Table 4 V ∼ ± U and U , ∼ , an inverse barometric e individually could explain an average 50 % SLR vari- ] together are used to estimate the daily-mean SLR 1 measured and estimated SLR is plotted in Fig. 10 for U V P − is , P V A A e U individually are able to account for an average 45 % of , & V P U and , A are able to explain an only average U V 1 cm mb P , ] together are used to regress the daily-mean SLR, the total Var A U P and ∼ − increases marginally to 49 % (Table 4). As stated earlier, along the A at Gopalpur, Gangavaram and Kakinada respectively. The variations , V e ◦ and V , results in the SLR variability. The relation between sea-level and atmo- , V U P , U A U and 50 ] together are used to multi-linear regress the daily-mean SLR as shown in ◦ P individually are able to account for an average 34 % of daily-mean SLR variabil- and A 38 % only, when regressed individually. The total Var P respectively. Similarly, in BOB the local shoreline angle with respect to North is ] is plotted in Fig. 9a. It is observed that the estimated daily-mean SLR during E1 V , , 45 ◦ ∼ A P 69 %. Daily-mean U, V and estimated SLR obtained by independent variables [ ◦ , V A ) towards land(sea) will give rise to increase(decrease) in SLR due to wind stress. U ∼ , In BOB, the daily-mean At Ratnagiri in AS 22.4 (29.7) cm, i.e. the estimated SLR is 24.7 % less than the measured daily-mean 52 19 , U U served to dominate with a range of estimated SLR follows the forcingmeasured of daily-mean V. Figure SLR 10a.2 at∼ is Gopalpur, plotted during with the E2SLR estimated the (Table and 5). estimated(measured) It SLR5 is is January also 2012, observed whereas thatGangavaram, the the estimated measured SLR SLR falls remainsdaily-mean to SLR high zero variability. ( When byto all 30 the regress December, three 2011. the variables At daily-meanwinds [ SLR, are the plotted Var in Fig. 10b.1, where the daily-mean along-shore ( east coast of Indiasea level. in Figure BOB 10a.1 the showsduring E2 the positive(negative) favouring the sea-level fall(rise).and However, by along-shore 1 component January of 2012 wind both -U(V)level turns the rise(fall). cross- landward(Northward), Sea-level appears imposing to a sea- be influenced more by alongshore wind, where the level during E1 (Fig. 9c.1),of the however the measured daily-mean estimated SLR SLR and is is able less to by peakGopalpur, Gangavaram only and up Kakinada. to The half tober(January) monthly for Var all the three stationsand in BOB as shown inity. When Fig. all 11b. At the Gopalpur, threein variables Eq. [ (1), the Var comparable response with measured daily-mean SLR,(Table 5). with a At minor Karwar overshoot (Fig. by 9c), age [ Fig. 9c.2 (Table 4). At Karwar also the level at Verem (Fig. 9b.1), still the estimated daily-mean SLR is able to reproduce the as presented in Fig. 9b.2.as The shown monthly in Var Fig. 11a. During E1, the is able to peak up toand the Table measured 5). daily-mean The SLR, monthly which is Var and less Fig. by 11a). However, inable to November explain 2011, the when SLR21 E1 % variability occurred at up [ all to thedaily-mean three sites in AS andSLR BoB variability (Fig. (Table 11 4). andlocations Table The 4). in total At AS, Verem Var (Fig. when 9b), [ the and in BOB the positive(negative) ability, when [ is V − ∼ in spheric pressure is ( Since the study regionwards being north in with the theTherefore, Northern coast in at Hemisphere, AS its the the right along-shore positive(negative) will winds increase to- the sea-level due to Coriolis force. variables individually. Then all theused three to independent regress variables the [ daily-meanand SLR. 10. Results are The listed cross- in andline Table 4 along-shore angles and components with plotted are in respect estimatedestimated Figs. to using 9 at North the Ratnagiri, local from Verem shore- Google and Earth. Karwar In with AS, respect the to local North shoreline is angle to know, the contribution to the SLR variability by the various surface meteorological 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ac- e ). The V . During E2, 1 ] together are − P is small in Jan- A 6 % (Table 5). At , e ∼ V 44 %. The Var , 10 m s ∼ U 13.8 cm) compared to ∼ ∼ − ordable to limited-budget ff 70 %. Var ∼ 65 % (Table 4). At Kakinada also the ∼ orts. ff 590 589 individually are able to account for an average P A increases to shore experience large waves, but little storm surge e ff and V , ) established by CSIR-NIO could play an important role in for December 2011 which is 63 %. Also the measured daily- U e ect the level of surge in a particular area. For example areas ff 570 km from Gangavaram as shown in Fig. 1. The slope of the conti- ∼ 237 (360) km to Thane. The highest surges usually occur to the right of the http://inet.nio.org/ ∼ ), as explained by Var winds (Fig. 10c.1), appears to dominate with peaks up to V This study attempts to investigate the meteorologically induced surges and water We summarise the response of sea-level of the two events in AS and BOB. The − 4 Conclusions It is being realisedmeteorological increasingly that measurements a along nearas real-time the ICON network coastal ( of and sea-level and Island surface locations of India such (SLOSH, 2003). At Gangavaram, thethe daily-mean other SLR sites is in low BOBseen ( in (Table 5). Fig. However, 5b.1. we Alsoof observe note Cuddalore distinct that harbour between when oscillations 01:00 Thaneis as crossed and observed the 02:00 at UTC Tamil Nadu Mandapam of coast andproximity 30 just Tuticorin, December even south though 2011, Mandapam(Tuticorin) no isstorm distinct in track close surge (travelling with the storm) at approximately the radius of maximum wind. and duration of the(E2) event, track the is distancenental from shelf the will source alsowith a etc. shallow The slopes of distance theand of continental areas Thane shelf with (as deep in water AS) just o will allow a greater storm surge This persistence of high daily-mean SLR state may be attributed to: intensity, direction to remote forcing. Inpeaks BOB, and the prolonged SLR falls response during to E2, which E2 the is estimated of SLR a is plateau not shape able with to capture. rising counted by local surfaceuary meteorological at parameters all the is al. locations (2010), of multi-linear regression the analysis present (everyresolve the two study dependence month (Table of duration) 4). sea was level In also onVerem, a used various Goa. forcing to similar parameters During for study the 2007 by and summerattributable 2008 Mehra to monsoon at wind et (May–September), was the up seait to level 47 reduced % variability and to 75 %