El Niño Effects on Goleta Coast Wave Climate

By Tina Nguyen

Summary• Research question: How does El Nino affect frequency

and magnitude of large swell events on Goleta coast during December, January, February

• Preliminary work – investigate relationship between large swell events and El Nino

• Following previous study of Seymour et al 1984• Data did not support Seymour’s correlation of large swells

with Oceanic Nino Index (ONI) – Seymour used data from Harvest buoy– This study used Goleta Point buoy

• Study did showed annual increase of frequency of waves during January – possible change in EN or wave climate

Methodology

• El Nino can increase large swell events in two

ways:– 1. number of storms remains constant but magnitude

of each storm increases = overall increase of large swell events (over 2m).

– 2. magnitude of storms remains constant but frequency of storms increase = increased probability of large swell events given the same distribution of swell heights.

Methodology cont’d

• Downloaded Goleta buoy data from Coastal Data Information Project (CDIP)

• Histogram of daily max wave heights (Hs) showed 74% of measurements below 2 m

• Defined large swell event as over 2 m threshold• Summarized number of days over 2 m to

measure frequency of large swell events• Graphed frequency against sea surface

temperature anomalies (SST) from ONI to investigate correlation

Results

• No consistent pattern between anomalous sea surface temperature and frequency of high waves was evident

• The 2009/2010 El Nino showed a correlation with increased magnitude and frequency of waves

• The 2005-2008 period does not show any consistent relationship

• Recognized increasing pattern in frequency of maximum wave heights during the month of January

2002-03 2003-04 2004-05 2005-06 2006-07 2007-08 2008-09 2009-100

2

4

6

8

10

12

14

16

18

20

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Goleta Buoy Wave Height > 2m and Oceanic Nino Index

December January February +/- 0.5 °C SST Anomally

Num

ber o

f Day

s > 2

m

+/- 0

.5° C

(Se

a Su

rfac

e Te

mpe

ratu

re A

nom

aly)

Discussion and Future DirectionsThe Goleta buoy is affected by wave shadowing from Channel

Islands and Point Conception, possibly obscuring El Nino effects

• Further research should use Harvest Platform buoy data since it is more exposed to all North Pacific storm activity

• longer time series including strong El Nino events (1982-83 or 1997-98) is necessary to understand decadal impacts of El Nino

• Data from multiple buoys is needed – one location is not representative of entire region

• Parameters such as wave period and swell direction should also be analyzed

• The annual increase during January presents an opportunity to assess possible climate change effects

Wave shadowing