Impacts of enhanced central Pacific ENSO on wave climate and headland-bay beach morphology

It is now widely recognized that El Nino-Southern Oscillation (ENSO) occurs in more than one form, e.g. eastern and central Pacific ENSO. Given that these various ENSO flavours may contribute to climate variability and trends in different ways, this study presents a framework that treats ENSO as a continuum to examine its impact on precipitation, and to evaluate the performance of the last two generations of global climate models (GCMs): CMIP5 and CMIP6.Uncertainties in the location and intensity of observed El Nino and La Nina events are assessed in various observational and satellite-derived products (ERSSTv5, COBESSTv2, HadSST1 and OISSTv2). The probability distributions of El Nino and La Nina event locations, and intensities, slightly differ from one observational data set to another. For instance, La Nina events are more intense and more likely to occur in the central Pacific using COBESSTv2. All these products also depict consistent decadal variations in the location and intensity of ENSO events: i) central Pacific ENSO events were more likely in the 1940/50s and from the 1980s; ii) eastern Pacific ENSO events were more likely in the 1910/20s and 1960/70s; iii) La Nina events have become more intense during the 20th and early 21st centuries.These fluctuations in ENSO location and intensity are found to impact precipitation consistently across diverse global precipitation products (CRUv4.03, GPCCv8 and UDELv5.01). Over southern Africa, for instance, more intense eastern (central) Pacific El Nino events are found to favour drought conditions over northern (southern) regions during austral summer. By contrast, over the same regions, more intense La Nina events favours wet conditions, while the location of these events has little effect on precipitation. Over West Africa, ENSO locations favour a zonal (E-W) rainfall gradient in precipitation during boreal summer, while changes in ENSO intensity modulate the strength of the meridional (N-S) rainfall gradient.Using both historical and pi-Control runs, we demonstrate that most CMIP5 and CMIP6 models favour either eastern or central Pacific ENSO events, but very few models are able to capture the full observed ENSO continuum. Regarding ENSO impacts on worldwide precipitation, contrasted results appear in most models.

Download Full-text

INFLUENCE OF EL NINOS ON CALIFORNIA'S WAVE CLIMATE

Coastal Engineering Proceedings ◽

10.9753/icce.v19.39 ◽

1984 ◽

Vol 1 (19) ◽

pp. 39 ◽

Cited By ~ 5

Author(s):

Richard J. Seymour ◽

R. Rea Strange ◽

Daniel R. Cayan ◽

Robert A. Nathan

Keyword(s):

Southern Oscillation ◽

Strong Association ◽

Time History ◽

Threshold Value ◽

Wave Climate ◽

Central Pacific ◽

Large Wave ◽

The North ◽

Northern Summer ◽

Storm Waves

Waves with exceptional height and periods caused severe damage along the coast of California in 1982-83. Because these large wave events coincided with a strong El Nino-Southern Oscillation (ENSO) climatic anomaly, which occurs 20-25 times per century, there was interest in determining if the extreme waves resulted from the ENSO or its related features. The meteorological setting featured a very large and intense low pressure zone over the north-central Pacific. Associated with this Pacific-wide pattern, a series of large mid-latitude storms developed at about weekly intervals and produced exceptionally long fetchs directed at the California Coast. Two time series of extreme wave events, using buoy data after 1981 and hindcasts before, were used covering the period from 1900 to 1984. One series considered waves with significant heights greater than 3 m (10 ft) and the second for those greater than 6 m (20 ft.) These were compared with a time history of ENSOs for the same period. A strong association was established between northern hemisphere winters during ENSO years and large wave events in Southern California. Strong ENSO winters had the largest storm waves, moderate ENSOs less intense waves, and weak ENSOs tended not to have storm waves greater than the threshold value used in this study. The correlation between large waves and ENSO years is significant at the 1% level. The correlation between lack of large waves and non-ENSO years is significant at the 0.5% level. Because of the great southerly extent of the most energetic storms, a large number of energetic wave trains approach the coast from the west, rather than the northwest, as previously assumed by many. ENSO winters are responsible for producing all of the wave events in this study with both heights greater than 6 m and periods of peak energy longer than 19 seconds. Five out of nine eastern Pacific tropical storms making landfalls on California in the 85 year period occurred during the late northern summer of ENSO years.

Download Full-text