El Nino Period Research Articles

Temporal and Spatial Patterns in the Diet of the Common Murre in California Waters

We investigated temporal and spatial variation in the diet of the Common Murre Uria aalge, the most abundant, locally breeding seabird of the central California continental shelf. We collected murres in coastal, mid-shelf, and outer-shelf waters of the Gulf of the Farallones during the murres' pre-breeding (March-April), breeding (May-August), and wintering (September-February) periods, 1985-1988. Diet samples formed persistent groups as a function of these six spatio-temporal combinations of murre foraging habitat and life-history periods. Temporally, diets varied on a seasonal and interannual basis, with diets during winter and El Nino periods being the most disparate. Spatially, diets differed among the three habitats, independent of time. During the pre-breeding season after the onset of upwelling, euphausiids and juvenile rockfish (Sebastes spp.) became prevalent in the diet. Diets were least diverse during the breeding season because of the dominance of rockfish, especially among murres foraging in mid- and outer-shelf habitats. Other important prey were also significant for commercial or sport fishing: Engraulis mordax and Clupea harengus in coastal waters, Merluccius productus and Loligo opalescens in mid- and outer-shelf waters, and surfperch Cymatogaster aggregata and Brachyistius frenatus in coastal and outer-shelf waters (near reefs), respectively. Results support a hypothesis that diet varies as a function of where murres forage. Hence, if the most characteristic prey of one habitat disappears, murres switch foraging areas, bringing a switch in diet. Owing to environmental changes in the region, murres may be losing the option of prey switching as a strategy to maintain an adequate intake of food.

Carbon export and regeneration in the coastal upwelling system of Monterey Bay, central California

In order to quantify the role of coastal upwelling regions as source or sink areas for carbon, the relationships between particulate organic carbon (POC) production, export, remineralization, and accumulation were examined in Monterey Bay from 1989 through 1992. During a normal upwelling year (1989-90), a high positive correlation (r = 0.91) is observed between biweekly primary production and POC export at 450 m. Primary production values range from 500 mgC m -2 d -1 during the winter, to 2600 mgC m -2 d -1 in the spring and summer upwelling months. Corresponding deep-water (450 m) POC fluxes vary from a minimum of 10 mgC m -2 d -1 in December, to 120 mgC m -2 d -1 in May. In contrast, the mid-1991 through 1992 data sets obtained during the '91-92 El Nino period, show a relatively poor correlation (r = 0.23) between productivity and carbon export. Calculated ratios of POC export to POC production (defined as e-ratios) display a trend for the three-year data sets in which the e-ratio values are greatest during periods of low productivity and decrease to minimal values when surface production is high. Upwelling-induced, offshore Ekman transport of organic matter and probable seasonal changes in the planktonic community structure are the mechanisms likely to be responsible for the e-ratio trends. Based on the data sets reported from this work, a simple box model of the annual export and regeneration of particulate organic carbon is presented for the Monterey Bay region. An appreciable advective and/or recycling loss from the euphotic zone of 362.8 gC m -2 y -1 is estimated, representing primarily algal material transported offshore and/or recycled within the upper 100 m of the water column. Annual mid-water (∼100-450 m) and deep-water (>450 m) POC remineralization rates of 71.8 gC m -2 y -1 of 7.2 gC m -2 y -1 , respectively, are reported for Monterey Bay. The average POC rain rate to the underlying slope sediments is sufficient to satisfy reported benthic utilization requirements without invoking an additional input source of POC via deep lateral advection and/or the downslope movement of particulate material.

Response process of ocean to atmospheric forcing and optimal response frequency in the CZ ocean model

Ocean response to atmospheric forcing in the CZ ocean model is analyzed. The results show that Nino 3 index from the CZ ocean model driven by linear composite of biennial, ENSO and even annual time scale wind stress anomalies is consistent well with composite of responding two or three components of observed Nino 3 index during the El Nino period while the La Nina phenomena cannot be reproduced by the linear composite. It implies that linear response process for ocean response to atmospheric forcing is dominated during the El Nino period while nonlinear response might be main process during the La Nina period.

Numerical study for characteristic change of Asian summer monsoon circulation and its influence mechanism during the El Nino period

In this paper, the relation between Asian summer monsoon circulation and sea surface temperature anomalies over equatorial central-eastern Pacific is investigated by using a global spectral model. This model has nine layers in the vertical and the model variables are represented in the horizontal as truncated expansions of the surface spherical harmonics with rhomboidal truncation at wave number 15. The model involves comparatively complete physical processes and parameterizations with mountains.

The operational seasonal forecasting of the summer rainfall in China

The paper presents a review of the success and failure of the practical results from summer drought and flood forecasts and seasonal precipitation forecasts in the period from 1976 to 1985. An analysis is made on the anomaly of the general circulation wihch gives rise to summer precipitation and drought-flood occurrences in the country. It is proposed that the subtropical high over the West Pacific, the South Asia high and middle-latitude westerlies are the major synoptical regimes producing summer weather in China. The analysis focuses on the features of low-frequency oscillation and abnormality of the West Pacific subtropical high in the monthly 500 hPa mean charts, and on their interactions with the sea temperature of the North Pacific and the Equatorial Pacific. The result shows that there exist quasi-cycles of 3–4 years, 11 years and 19 years or so in the subtropical high with the feature of strong persistence and seasonal changes. There is a rather good correlation between the behaviour of the subtropical high and changes in the cold current area in the East Pacific, and especially during the El Nino period, there is an obvious coupling with abnormal changes of the intensity of the subtropical high. Analysis is also made on the effect of the thermal condition of the Tibetan Plateau, the Northern Hemisphere westerly circulation and the astronomical factors on the West Pacific subtropical high, the South Asia high and precipitation in the rainy season in China.

西部太平洋雲量の長期変動

Long-term variations of heat sources and their spatial distributions in the western Pacific region are examined by using satellite-observed high-cloud amount data from 1978 to 1983. There exist large seasonal variations with maximum cloud amount in the summer hemispheric tropical regions. Spatial distributions of cloud amount are largely affected by summer and winter monsoons over Southeast Asia and Australia.Large interannual variability of cloud amount is confined in the equatorial region during northern winter, but large variations are found not only in the equatorial region, but in the northern subtropics around 20°N and in the middle latitudes near 35°N during summer.Two dominant cloud anomaly patterns are found by correlation computations and Empirical Orthogonal Function (EOF) analysis. The first anomaly pattern (El Nino pattern) is the east-west oscillation between the equatorial central Pacific and the western Pacific. This pattern was significantly amplified during 1982-83 years corresponding to the El Nibo event. The second anomaly pattern (South Japan pattern) is the north-south oscillation between northern subtropics and middle latitudes extending from East China to the dateline. This pattern becomes most evident during northern summer.Cloud anomalies along the equator during 1982-83 show that positive anomalies near 150°E started to move eastward in May - June 1982, reached the central and eastern Pacific in late '82 and continued to stay in the eastern Pacific till next summer. The large portion of the western Pacific regions was occupied by intense negative cloud anomalies. During this period cloud amounts along the mid-latitude storm tracks from East China Sea to Northwest Pacific increased probably due to enhancement of extratropical cyclone activities.During the summers of 1978 and 1981 convection centers in the tropical western Pacific are abnormally shifted northeastward from the normal position near Philippines to western Pacific subtropics around 20°N, 140°-150°E. Cloud amounts both in mid-latitude regions to the north of the convection centers and in the equatorial regions to the south are greatly reduced and Japan Islands have experienced hot summers during these years.Relationships between variations of cloud amount and sea surface temperature (SST) in the tropical western Pacific are examined. EOF analysis of SST shows that SST variations are dominated by the first eigen mode with large amplitudes in the tropical western Pacific east of 140°E and from the equator to about 20°N. the amplitude of this mode significantly increases in 1982-83 indicating that large negative SST anomalies appear in the vast tropical western Pacific regions during the El Nino period. The South Japan cloud anomaly pattern develops during summers when large positive SST anomalies in the tropical weatern Pacific appear. Correlation computations also indicate close relationships between cloud amount and SST.