Seymour Et Al. 1984 Influence of El Ninos on Californias Wave Climate

8/3/2019 Seymour Et Al. 1984 Influence of El Ninos on Californias Wave Climate

http://slidepdf.com/reader/full/seymour-et-al-1984-influence-of-el-ninos-on-californias-wave-climate 1/16

CHAPTER THIRTY NINE

INFLUENCE OF EL NINOS ON CALIFORNIA'S WAVE CLIMATE

Richard J. eymour, .ASCE 1) R. Rea Strange III ( 2 )

Daniel R. Cayan ( 3 ) Robert A. Nathan AM.ASCE ( 4 )

ABSTRACT Waves with exceptional height nd eriods aused evere amage

along the oast f alifornia n 1982-83. ecause these large wave events coincided with a trong l ino-Southern scillation E N S O ) climatic anomaly, hich ccurs 0-25 imes er entury, there was interest in determining if the extreme waves resulted from the ENSO r it s related features. he meteorological setting featured a very large and ntense ow ressure one ve r he orth-central acific. Associated with his acific-wide attern, eries f arge mid-latitude storms eveloped t bout weekly intervals and produced exceptionally long fetchs directed at the California Coast.

Two time series of extreme wave events, using buoy data after 981 and hindcasts efore, were used covering the period from 1900 to 1984. One series considered waves with significant heights greater than ( 1 0 f t ) nd the second for those greater than 6 m (20 f t . ) hese were compared with a time history of ENSOs for the same eriod. trong association was stablished between northern hemisphere winters during ENSO years and large wave events in Southern California. trong NSO winters had the largest storm waves, moderate ENSOs less intense waves, and weak NSOs ended ot o ave torm aves reater han the threshold value used in this tudy. he orrelation etween arge waves and NSO ears is significant at the 1% level. he correlation between lack of large waves and non-ENSO years is ignificant t he 0.5% level.

Because of the great southerly extent of the most energetic storms, a large number of energetic wave trains approach he oast rom he west, rather han he northwest, as previously assumed by many. NSO winters are responsible for producing all of the wave vents n his study with oth eights reater han 6 m and periods of peak energy longer than 19 seconds.

Five out of nine eastern Pacific tropical storms aking andfalls on California n he 8 5 year period occurred during the late northern summer of ENSO years.

(l)Hd.,Ocean Engr. Research Group, Scripps Inst. of Oceanography, La Jolla, CA

(2)President, Pacific Weather Analysis, Santa Barbara, CA (3)Research Assoc., Scripps Inst. of Oceanography, La Jolla, CA (4)Coastal Engineer, Moffatt & Nichol, Engineers, Long Beach, CA

5 7 7



578 OASTAL ENGINEERING -1984

INTRODUCTION

During t h e Winter of 1 9 8 2 - 8 3 , series o f xtraordinary storms attacked t h e coast of California. horeline damage was e v e r e , particularly i n Southern C a l i f o r n i a , and was accompanied by unusual coastal plain looding n many a r e a s . he extreme sea levels causing this flooding and an assessment of h e nearshore waves and their impacts are discussed i n t w o papers i n these proceedings ( s e e Flick and Cayan,1984 nd Walker,Nathan,Strange and S e y m o u r , 1 9 8 4 . ) he ave fields associated with hese torms ttracted particular attention because of h e xtremely long peak periods as well as the great wave h e i g h t s . o many observers, the number and intensity of hese storms exceeded that of any winter within m e m o r y .

The year 1 9 8 2 , which immediately preceeded the most intense torms during January-March of 1 9 8 3 , was climatologically exceptional. e now know that a very strong l Nino - Southern Oscillation ( E N S O ) event began i n t h e late spring of 1 9 8 2 . t the t i m e , the ime equence of equatorial oceanic warming nd t r a d e wind reversal was s e v e r a l months l a t e r t h a n ost previous N S O s , ausing ively ebate mong oceanographers and climatologists as o whether there really was an ENSO occurring ( s e e K e r r , 1 9 8 3 . ) he inpact o f ENSOs on productivity i n South American coastal waters has been well studied f o r many y e a r s . Only r e c e n t l y , motivated i n part by the extreme nature of h e 2 - 8 3 E N S O , have cientists understood the global npacts o f t h e e v e n t , including droughts and excessive rainfall over large areas outside of t h e t r o p i c s . F o r a review of ENSO s e e P h i l a n d e r , 1 9 8 3 . ) here was a second major climatological perturbation almost coincident with t h e onset o f h e ENSO - the eruption of the Mexican v o l c a n o , E l C h i c h o n . Although i t s t o t a l ejected mass was much smaller t h a n , s a y , ount S t . H e l e n s , i t was one o f those rare eruptions that results i n very l a r g e quantities o f sulfuric acid i n the t r a t o s p h e r e . his contaminant, with a long persistence, spread completely around the globe i n a broad band straddling the e q u a t o r . here i s evidence from historical climate records that this kind of ruption can have pronounced effects on global climate ( s e e S i g u r d s s o n , 1 9 8 2 . ) he superposition of the strong ENSO and E l hichon makes i t very difficult to sort out t h e climatic effects of each e v e n t . he severity of the 1 9 8 2 NSO may even have been augmented by t h e nfluence of he E l hichon c l o u d , but o u r present level o f understanding of climatology does not allow us o confirm o r reject such i n t e r a c t i o n s .

Volcanos rarely vent sulfides all the way to the stratosphere, u t ENSOs o c c u r erhaps 20 times i n a c e n t u r y . t i s therefore i m p o r t a n t , from a wave climatology standpoint, at the least to determine i f E N S O s are likely o have been paramount n riving these severe s t o r m s . Therefore, t h e authors decided to test the relationship between ENSOs and large wave events by comparing time series from historical r e c o r d s .



EL NINOS INFLUENCE 79

THE 1982-83 LARGE WAVE EVERTS OFF CALIFORNIA

The NOAA observation buoy moored at approximately 35 N latitude and 121 W longitude measured si x large ave vents, ach elated o massive storm n he acific Basin, that occurred in the period from December,1983 to March,1983. he significant wave height exceeded 6 ( 2 0 f t ) n ach f hese vents, s hown n able . hese observations were made in deep water in unsheltered offshore locations.

The storm of 10 February, 1983, which produced the longest eriods of this eries, was studied in detail (see Earle et al., 1984.) sing all of the NOAA buoy data, this work showed that the ignificant ave height at he ite losest o the storm was 12.9 m ( 4 3 f t ) and that there was considerable energy up to periods s ong s 5 econds. This energy level would predict a maximum wave height of about 24 m ( 79 f t . )

In later sections of this paper, it will be shown that these storms rank as very extreme events in recent history.

THE METEOROLOGICAL SETTING

From a meteorological standpoint, the 1982-83 ENSO winter was ost extraordinary, especially ver he acific nd adjacent continental margins. ot only was the Gulf of Alaska-Aleutian low pressure enter unusually deep a s s ften he ase with northern hemisphere ENSO winters), but the low was, on average, large enough in areal extent and displaced eastward ufficiently o ffect he est oast nd particularly California. his as not always been the case with ENSO winters (see Namias and Cayan, 1984.) igure hows he eparture from normal f he 7 00 millibar ( m b ) height surface for winter, which is nearly equivalent to the anomalous pressure pattern at bout m (10,000 f t ) loft. t s shown to be abnormally low (negative) in a broad region centered in the southern Gulf of laska, nd ery igh (positive) in he entral acific ubtropics. ymptomatic of this pressure distribution were the frequent assive nd igorous torms that tracked cross he entral North Pacific to make landfall along virtually the entire West Coast of the United States. n a more ususal winter, storms would be confined to landfalls at latitudes much further north.

The anomalous atmospheric angular momentum ssociated ith hese wind fields as studied by Rosen et al., (1984). his work shows that the transfer of angular momentum between the earth and he tmosphere was sufficient o hange he length of the day by a few milliseconds during the winter of 1982-83.

Note that, although these storms were associated with n NSO a tropically ased henomenon), hey ere efinitely xtratropical disturbances. his is shown in Figure 2 y he yclone racks or March 1983. igure shows an infrared satellite image of two of the March 1983 storms. he storm fronts show reater evelopment nd more southerly isplacement han sual. lso note that there is no obvious connection of these storm systems with the tropics.



5 8 0 COASTAL ENGINEERING-1984

FIGURE 1 Winter 1982-1983 mean 7 0 0 m b . eight anomaly i n tens o f f e e t . his i s roughly analogous t o t h e s e a l e v e l pressure a n o m a l y . inter i s efined a s December hrough F e b r u a r y . Anomaly calculated against ean o f 1 9 4 7 - 1 9 7 2 w i n t e r s .



EL NINOS NFLUENCE 5 8 1

S 3

o nj M 4J

1—1 e S 3 o tH 4J a (0 i-l r - - s CN

•H 1

J (0 u U 4 > -M Xi X J- l 3 L (0

0 1 s

a > c 1 0 o rH M o < p & .s

•H s U •H o (0 A < 2 5S M M s £i



582 COASTAL ENGINEERING-1984

FIGURE 3 Satellite infrared m a g e v e r orth P a c i f i c , arch , 1 9 8 3 . i g h clouds ( c o l d e s t ) are hown n white. ow clouds w a r m ) re not distinguishable e r e . ote extensive r o n t a l ystems xtending southward t o 30 deg N , nd lack o f onnection t o ntertropical convergence z o n e near e q u a t o r .



EL NINOS INFLUENCE 83

TABLE NOAA BUOY OBSERVATIONS OF WAVES PROM MAJOR STORMS

WINTER 1982-83

DATE SIG.HT. ( m ) MAX . PERIOD DIRECTION

01 EC 2 6.4 14 295 18 EC 2 6.4 20 288 25 AN 3 6.1 17 278 27 AN 3 7.3 22 279 10 EB 3 6.7 25 2a 01 A R 83 8.2 20 258

These very l a r g e and intense low pressure centers esulted n fetchs on h e r d e r f 1000 km ( 5 5 0 n m ) and wind speeds up to 30 m/s ( 6 0 k t s . ) revious empirical m o d e l s , still widely used t o d a y , ould predict peak

periods

of

only

about

7 seconds f o r s u c h conditions.

Contemporary spectral wave generation models containing nonlinear wave interaction t e r m s , o w e v e r , re capable f predicting the very long periods actually generated i n these s t o r m s .

I t can be seen from Figure 1 that the wind vectors can be xpected to rotate to t h e north a s he storms pproach the continent. n typical winters, this northward shift occurs ( o n a v e a r g e ) about 2200 km ( 1 2 0 0 n m ) offshore. t this p o i n t , the winds no onger ontinue o increase wave h e i g h t . ispersion causes the s w e l l to decay over these l o n g d i s t a n c e s , reducing the height of the waves as they approach he s h o r e . uring t h e winter o f 1 9 8 2 - 8 3 , because of the very large s i z e of t h e low pressure zone and the increased strength of the westerlies, the average decay distance was educed to about 1600 km ( 9 0 0 n m . ) hese factors account f o r the increase i n the swell height during these storm wave e v e n t s . t should also be noted that the locally generated waves may be ravelling orth almost orthogonally to the s w e l l , producing a very confused s e a state i n deep water.

HISTORICAL WAVE DATA FOR THE CALIFORNIA COAST

Systematic wave measurements i n deep water off the West Coast o f t h e United States have been available only since 1 9 8 0 . herefore, any meaningful historical ssessment must epend argely pon ave hindcasts. ontemporary hindcasts, based upon reliable pressure field data and atellite m a g e r y , an provide wave nergy spectra and directional stimates with atisfactory accuracy o r ngineering a n a l y s e s . o w e v e r , f o r pre-satellite years, and particularly prior o the mid-1940's, h e meteorological ata become less satisfactory and t h e accuracy o f the wave hindcasts i s degraded. here are a number f storm hindcast tudies hat have een performed f o r t h e California



5 8 4 OASTAL ENGINEERING-1984

Coast ( e . g . , s e e Marine Advisers, 1960 and Meteorology nternational, 1 9 7 7 . ) hese works suffered from short observation periods a n d , i n at least one c a s e , from serious methodological roblems. he earlier works used a singular wave approximation, compared with the spectral approach now employed by contemporary hindcasters. ather han attempting to patch together the work of several hindcasting studies i n an attempt to acquire a long enough time history, we decided to use the work o f single hindcaster which spanned the whole interval from the inception of meteorological data (approximately 1 9 0 0 ) to the advent o f continuous deep water measurements i n late 1 9 8 0 . ne of us ( R R S ) has prepared such a s e r i e s . t was hindcast f o r location n Southern California at a latitude of about 35 N . his series was an attempt to identify wave trains expected to have a ignificant m p a c t n the shoreline. herefore, t ncluded only those events with deep water approach directions i n the zone between SW and WNW. aves approaching more obliquely would be diminished considerably by refraction as they approached t h e s h o r e . urther, the waves were ranked by their power ( e n e r g y multiplied by p e r i o d . ) his resulted i n a list of 59 storms i n which t h e esulting offshore significant wave height exceeded 3 m ( 1 0 f t ) , a l l having periods equal to or exceeding 1 2 s e c o n d s . he tropical cyclone o f S e p t e m b e r , 1 9 3 9 , a major wave event i n Southern California, was added f o r t o t a l of 60 s t o r m s . hese storms are listed i n Table I I .

A second series was obtained by considering only the very largest e v e n t s . he threshold ignificant wave height was raised to 6 m ( 2 0 f t . ) he second series contains only 18 storms because of t s higher limit v a l u e , as shown i n Table I I I .

I t should be learly recognized that h e possible quality of hindcast decreases with the a g e of the d a t a , particularly prior t o , the 1 9 5 0 ' s . t i s likely that some major storms i n the early years were excluded because here was insufficient pressure field resolution and accuracy to estimate the r e a l wind s p e e d s . his i s particularly t r u e f o r s m a l l , n t e n s e torms ike ropical y c l o n e s . t s lmost impossible to hindcast hese t o r m s rior o the availablity o f satellite i m a g e r y . owever, ince no eries o f his ength had previously been published, nd since he work sed a onsistent methodology throughout, e e l t hat hey would make valuable contribution t o o u r knowledge of the wave climate off California. HISTORICAL RECORDS OF ENSO COEDITIOKS

Using anomalies i n the surface barometric pressure n he Indian and Pacific O c e a n s , combined with observations of fisheries i n Peru and other similar a t a , Quinn et a l . 1 9 7 8 ) were able to develop a series of ENSO events covering more than 200 y e a r s . hey also ated each event as s t r o n g , oderate o r w e a k . he ENSOs since 1900 from this record are s h o w n i n Table I V . uinn et al's ENSO series dentifies events according o their nset y e a r s . o r o u r purposes, i t i s the winter following the o n s e t , hen the mid-latitude onnections are s t r o n g e s t , that would have possible consequences f o r Pacific waves.



EL NINOS NFLUENCE 8 5

TABLE I

EXTREME W A V E EPISODES XCEEDING M . (BASIC SERIES) 1900 984

DATE SIG.HT. (m) MAX . ERIOD DIRECTION

13 M A R 5 8.8 15 247

17 O V 5 3.3 17 286

31 DEC 7 5.3 16 282

12 M A R 2 3.2 12 220

26 AN 4 5.8 13 223 03 EB 5 7.5 14 235

01 AN 8 3.7 16 280

12 EB 9 5.3 12 299

20 DEC 0 4.7 13 301

15 OCT 23 3.7 16 296

01 EB 26 6.9 15 257

03 AN 27 5.8 20 287

06 O V 28 4.0 17 294

01 AN 1 3.9 16 276

28 DEC 1 7.4 18 288

19 DEC 5 4.7 16 267

13 DEC 7 4.5 16 272

06 AN 9 7.9 19 285

25 EP 9 4.5 15 205

24 AN 0 4.3 16 267

25 DEC 0 5.7 16 270

20 OCT 1 3.3 17 294

30 DEC 5 3.9 19 285

13 EB 7 3.9 16 265

04 O V 8 4.7 18 300

15 O V 3 5.7 17 269

15 AN 8 3.1 22 280

2 6 AN 58 6.8 14 259

05 H R 8 7.7 18 289

16 EB 9 5.1 14 244 09 FEB 0 8.1 19 295

2 2 DEC 0 3.4 17 276

31 AN 63 4.2 16 260

10 EB 3 5.9 15 256

19 O V 65 4.0 15 277

07 DEC 7 4.0 15 298

06 EB 9 4.7 13 222

04 DEC 69 3.6 17 278

06 DEC 9 4.9 22 274

14 DEC 9 5.7 17 290

19 DEC 9 4.7 18 281

26

EC 2

4.1

15

289

21 EB 7 5.2 18 280

29 OCT 77 5.5 20 299

16 AN 78 6.0 13 240



5 8 6 COASTAL ENGINEERING-1984

TABLE II (cont.)

01 JAN 80 17 FEB 80 22 JAN 8 1 28 JAN 8 1 13 NOV 8 1 01 DEC 8 2 18 DEC 8 2 25 JAN 8 3 27 JAN 8 3 10 FEB 8 3 13 FEB 8 3 01 MAR 8 3 14 NOV 8 3 03 DEC 8 3 25 FEB 84

4.7 20

6.1 18

4.3 20

7.0 17 4.9 18 6.4 14

6.4 20

6.1 17 7.3 22

6.7 25 4.9 17 8.2 20 5.0 17 7.0 17 6.4 17

TABLE III

27 2 249 258 26 2 284 295 288 27 8 27 9 281 26 8 258 290 285 300

EXTREME WAVE EPISODES EXCEEDING 6 M. 1900 - 1984

DATE SIG.HT. (m) MAX . ERIOD DIRECTION

13 M A R 5 8.8 15 247

03 EB 5 7.5 14 235

01 EB 26 6.9 15 257

28 DEC 1 7.4 18 288

06 AN 39 7.9 19 285

2 6 AN 58 6.8 14 259

05 APR 8 7.7 18 289

09 FEB 0 8.1 19 295

17 EB 0 6.1 18 249

28 AN 1 7.0 17 262 01 DEC 2 6.4 14 295

18 DEC 2 6.4 20 288

25 AN 3 6.1 17 278

27 AN 3 7.3 2 2 279 10 FEB 3 6.7 25 281

01 M A R 3 8.2 20 258

03 DEC 3 7.0 17 285 25 EB 4 6.4 17 300

In four cases, one year adjustments were made in he nset ears suggested by uinn t al. he 1929 onset was changed to 1930 and the 1905, 1914 and 1939 onsets were changed to wo ear pans 1904-05, 1913-14, and 1939-40, respectively.) he basis for this was the timing of the eak f he outhern scillation a s etermined rom the Santiago-Darwin anomaly.) he onset year was djusted o rovide uniform condition hroughout he eries n hich he eak of the pressure anomaly occurred in the Spring or Summer. In ddition, he



EL NINOS INFLUENCE 5 8 7

TABLE V ONSET EARS F NSOS , 1900-1984

(From Quinn t al., 978) ONSET YEAR SEVERITY

1902 Moderate * 904-05 Moderate 1911

* 913-14 Strong

Moderate

1917 Weak 1918 1923

Strong Weak

1925 * 930

Strong Moderate

1932 Weak * 939-40 Moderate 1941 1943

Strong Weak

1951 Weak 1953 Moderate 1957

1965

Strong

Moderate 1969 Weak 1972 1976

Strong Moderate

* 98 2 Strong

* Modified from Quinn et a l . 1969 ENSO was eclassified from weak to moderate, i n t h e context o f t h i s s t u d y , because the pressure anomaly persisted o r more than a y e a r . he 1 9 8 2 E N S O , which occurred after the Quinn et a l . a p e r , was classified by us as s t r o n g . he ENSO predictions f o r the first half of the century are expected to be of higher quality than the wave hindcasts, since they did not depend upon h e density of pressure measurements. CORRELATIONS BETWEEN ENSO YEARS AND LARGE WAVE EVENTS

As was observed i n 1 9 8 2 - 8 3 , increased storminess as a result of an ENSO condition would likely o c c u r during the winter following o n s e t . Therefore, storms i n January through April of the year ollowing h e onset could be assumed to have been influenced by the E N S O .

Applying t h i s criterion to the time series of ENSOs and o f a r g e wave events produces the following r e s u l t s . o r t h e basic wave s e r i e s , 3 2 of t h e 60 wave events were associated with E N S O s . or the series of very l a r g e w a v e s , 12 of the 18 wave events were associated with E N S O s .



5 8 8 OASTAL ENGINEERING-1984

Not all ENSOs resulted i n large wave v e n t s . able V shows a comparison between the occurrence of l a r g e storms and the ENSO strength categories of Quinn et a l .

Table V shows that all seven strong ENSOs resulted i n a wave vent where t h e height exceeded m 1 0 t ) with an average o f 2 . 1 such events p e r E N S O . hree out o f seven of hese trong NSOs produced wave heights over 6 ( 2 0 f t ) f o r an average of 1 . 3 . ll but one of t h e nine moderate ENSOs yielded waves above 3 m , with an average of 1 . 7 events p e r E N S O . nly t w o of these produced waves above 6 and the average dropped

to

0 . 3 .

wo

f

h e

i v e weak ENSOs met the lower

height l i m i t with an average of 0 . 4 occurrences per E N S O . eak NSOs produced no wave events exceeding the 6 m l i m i t .

Table V shows a consistent series of elationships between ENSOs and large wave v e n t s . trong ENSOs result i n significant numbers of storms with waves exceeding both the 3 and t h e 6 m t h r e s h o l d s . Moderate ENSOs produce torms with waves exceeding the 3 m l i m i t , but not the 6 m v a l u e . eak ENSOs have only a slight tendancy to produce storm waves that exceed the 3 m t h r e s h o l d .

Eliminating the weak E N S O s , a o t a l f 6 strong and moderate events were recorded n h e 8 5 year period considered. llowing f o r the three multi-year e v e n t s , there were 19 ENSO years uring he 5 year interval hat would b e lassified as greater than weak e v e n t s . Considering the 3 m ( 1 0 f t ) threshold wave e v e n t s , there was an average of 0.71 events p e r year over all y e a r s . uring the moderate o r trong ENSO y e a r s , there was an average of 1.58 events per y e a r . pplying the Student's t test to determine the probability of the mean during these ENSO years exceeding the mean over all years by his a m o u n t , he probability was hown to be about 0.01 ( o n e chance i n a h u n d r e d . ) he mean value o f l a r g e wave events during non-ENSO years was found to b e 0 . 4 5 . he probability of the mean being this much lower than the mean over all years was f o u n d , by Student's t t e s t , to be ess than 0.005 ( f i v e chances out o f t h o u s a n d . ) h u s , the incidence of large wave events i n association with ENSOs and the reduction i n large storm waves during non-ENSO years are established tatistically ith ittle q u e s t i o n . WAVE APPROACH DIRECTIONS AND CHARACTERISTIC PERIODS

Because of t h e frequent winter torms hat are spawned by t h e Aleutian Low during most years, i t has generally been assumed that the track f o r major storms affecting alifornia s sually out of he northwest. able I h o w s , o w e v e r , hat a large number of severe storm waves come out of the w e s t . his i s shown n Figure 4 , hich plots t h e ncidence of wave approach irections f o r he Table I I s e r i e s . strong peak i s found at about 285 d e g . o r both the t o t a l data s e t and also the ENSO year s u b s e t . he ENSO year occurrences a l s o are observed to f a l l off rapidly at approach directions slightly n o r t h of this p e a k .



EL NINOS NFLUENCE 8 9

TABLE V

ASSOCIATION OF ENSOS AND LARGE WAVES

ONSET NUMBER OF LARGE WAVE EVENTS YEAR Central Southern

California California

STRONG NSOS

1911 1 0

1918 1 0 1925 1 1

1941 1 0

1957 3 2

1972 1 0

1982 7 6

M O D E R A T E NSOS

1902 0 0

1904-05 2 1 1913-14 2 1

1930 1 0 1939-40 3 0

1953 1 0 1965 1 0

1969 4 0

1976 1 0

W E A K NSOS

1917 1 0 1923 1 0

1932 0 0

1943 0 0 1951 0 0

Conventional wisdom has also suggested that severe storms along the California Coast produced periods of peak energy of no greater han about 19 s e c o n d s . he storms of 1982-83 showed very clearly that this limit was much too l o w . igure 5 depicts the incidence of peak periods i n the very l a r g e wave events contained n h e Southern California s e r i e s . t an be eadily seen rom Figure 5 that a l l storms that produced peak energy wave periods greater han 20 seconds ere associated with NSO y e a r s . his i s , of c o u r s e , consistent with the meteorological setting during most ENSO events i n which there are very l o n g fetchs directed at the California C o a s t .

TROPICAL STORMS

The pronounced warming of the surface waters along h e California Coast during strong E l Nino condition could be expected to allow the northward excursion of tropical cyclones ( h u r r i c a n e s ) n ate ummer and early a l l to latitudes excluded i n non-ENSO years. s previously n o t e d , i t i s not generally possible to develop a wave hindcast series



5 90 COASTAL ENGINEERING-1984

220 240 260 280 300

Wave Direction Deg) FIGURE

Number of occurrences of major wave vents rom various approach directions f o r events i n Table I I .

12 - M a jo r torms:

1900-1984

10 ^^~~~*Al l ears

8

6 - ~ENS0 ears

4

2 s* ~ _/\\

i 0 /

•

- Chance —1 -

12 14 16 18 2 0 2 2 Peak Period Sec)

FIGURE Number of occurrences of major wave vents with h e energy spectra peaked a t various wave periods. vents are from Table I I .



EL NINOS INFLUENCE 5 9 1

f o r t h e s e torms which a r e s o small i n diameter compared to a typical extra-tropical c y c l o n e . o w e v e r , Court ( 1 9 8 0 ) has compiled a record of hurricane tracks since 1 9 0 0 . his was extended through 1983 sing DeAngelis ( 1 9 8 3 ) . he tracks of these storms are shown i n Figure 6 . Of all o f t h e hurricanes observed n this p e r i o d , nly nine made landfalls in California. ive of these nine were i n ENSO initiation y e a r s , when warm water would be xpected along he West Coasts o f Mexico and California during the Fall hurricane s e a s o n . ne of these was t h e storm of 2 5 September, 1 9 3 9 , which i s one of the events i n the basic s e r i e s . herefore, he data suggest that late summer and fall hurricane-driven wave events n Southern California are much more likely i n ENSO years than during the intervening periods.

DISCUSSION AND CONCLUSIONS A very convincing statistical relationship has been demonstrated

between ENSOs and the large wave events that dominate the wave climate of Southern California. ecause ENSOs also tend to increase sea l e v e l along the California Coast i n rough proportion to their i n t e n s i t y , the c o a s t a l damage resulted from large waves will be exacerbated during ENSO e v e n t s .

The scheme adopted by Quinn et a l . 1 9 7 8 ) o r designating t h e intensity of t h e ENSOs i s i n good qualitative agreement with the number and intensity of l a r g e hindcast wave events i n California.

ENSOs appear to be among the more predictable o f the major lobal climate e v e n t s . herefore i t may be possible to forecast severe winter wave climates with some skill f o r the California C o a s t .

30 ^~^"NL

// Y§k on-

i ENSO ear Year

20 / f ( n VAN / 1 \ Y l * \M 1 } J \ V H \ v\l\

\/ \^ss^—L-vO r 0

FIGURE 6

Tracks f r o p i c a l yclones h u r r i c a n e s ) hat made Southern California during the period 1 9 0 0 - 1 9 8 3 .

landfalls n



592 OASTAL ENGINEERING -1984

Wave periods much longer t h a n typically assumed f o r this coast were r e c o r d e d . hese very l o n g periods have particular ignificance both f o r wave unup intensity and f o r drastic intensification of mooring loads on large floating structures with the potential o r eaching a near-resonant condition at approximately 0.04 h z . REFERENCES:

C o u r t , A , 1 9 8 0 . T r o p i c a l Cyclone Effects on California", QAA Tech Memo NWS WR-158, 4 1 p . DeAngelis, D . , 1 9 8 3 . Hurricane A l l e y " , Mariners Weather L o g 2 7 : 1 , p 3 4 - 4 0 . E a r l e , M . D . , K . A . Bush and G . D . H a m i l t o n , 9 8 4 . H i g h Height Long Period Ocean Waves Generated by a Severe Storm i n the Northeast Pacific Ocean during February 1 9 8 3 " , J o u r n . h y . c e a n . n p r e s s .

F l i c k , R . E . , and D . R . C a y a n , 1 9 8 4 . Extreme Sea Levels on the Coast of California", P r o c . 9 t h I n t l . onf.Coast. n g r . , H o u s t o n , T X .

K e r r , R . A . , 1983."Fading E l Nino Broadening S c i e n t i s t s '

V i e w " ,

cience

221:4614, pp 9 4 0 - 9 4 1 . Marine Advisers, 1 9 6 0 . D e s i g n Waves f o r Proposed Small Craft Harbor at Oceanside, alifornia", Report prepared f o r the U . S . rmy Engineer D i s t r i c t , Los Angeles, C A . Meteorology International, 1 9 7 7 . Deep-Water Wave Statistics o r he California C o a s t " , eport prepared o r he D e p t . f Navigation and Ocean Development, S a c r a m e n t o , C A . N a m i a s , J . , and D . R . a y a n , 9 8 4 . E l N i n o : mplications o r Forecasting", Oceanus 2 7 : , pp 4 1 - 4 7 . Philander, S . G . H . , 1 9 8 3 . E l ino Southern Oscillation Phenomena", Nature 3 0 2 : 5 9 0 6 , pp 2 9 5 - 3 0 1 . Q u i n n , .H., . O . Z o p f , . S . hort and . T . W . Kuo Y a n g , 9 7 8 . " H i s t o r i c a l Trends and Statistics of the Southern Oscillation, E l N i n o , and Indonesian D r o u g h t s " , Fishery B u l l . 6 : 3 , pp 6 6 3 - 6 7 8 .

Rosen R . D . , D . A . S a l s t e i n , T . M . E u b a n k s , J . O . D i c k e y , and J . A . S t e p p e , 1 9 8 4 . A n l ino Signal n Atmospheric Angular Momentum and Earth Rotation", Science 225:4660, pp 4 1 1 - 4 1 4 .

S i g u r d s s o n , H . , 1 9 8 2 . V o l c a n i c Pollution and C l i m a t e : he 1783 aki E r u p t i o n " , T r a n s . m e r . e o p h y s i c . nion 6 3 : 3 2 , pp 6 0 1 - 6 0 2 . W a l k e r , J . R . , R . A . N a t h a n , R . J . S e y m o u r , nd R . R . Strange I I I , 9 8 4 . " C o a s t a l Design riteria n Southern California", P r o c . 9th I n t l . Conf.Coast. n g r . , H o u s t o n , T X .

Documents

Seymour Et Al. 1984 Influence of El Ninos on Californias Wave Climate