Winter El Nino-Southern Oscillation Research Articles

Variability of the impact of El Niño–southern oscillation on sea‐level pressure anomalies over the North Atlantic in January to March (1874–1996)

AbstractSea‐level pressure (SLP) anomalies over the North Atlantic and European (NAE) sector (25–70°N, 100°W–50°E) and over a larger domain encompassing the entire North Pacific domain are studied to demonstrate that SLP anomalies (SLPAs) during boreal winter (January–March) vary widely between years characterized by the same El Niño–southern oscillation (ENSO) phase. The typical cold ENSO signal tends to be more stable than the warm one during the 1874–1996 period. The typical cold ENSO pattern (e.g. positive SLPA south of 55°N across the North Atlantic and negative SLPA in the northern North Atlantic) is similar to the positive phase of the North Atlantic oscillation (NAO) and occurs throughout the 20th century, except during the 1950s and 1960s when the basinwide westerlies are particularly slow. On the contrary, the typical warm ENSO pattern (e.g. positive SLPA from central Canada to Scandinavia and negative SLPA from the southeastern USA to central Europe, corresponding to the negative phase of the NAO) occurs mainly from 1930 to 1970. Another robust warm ENSO pattern is associated with a large positive (negative) SLPA between Newfoundland and western Europe (between Greenland and Scandinavia), and occurs mainly at the beginning and the end of the 20th century when the basinwide North Atlantic westerlies are strengthened. All these patterns stay statistically significant when the multi‐decadal variability is removed from the North Atlantic SLPA. It is shown that the low‐frequency variability of the north tropical Atlantic sea‐surface temperature anomalies could exert a modulating effect on the ENSO teleconnection. NAE SLPAs tend to be strong during warm (cold) ENSO winters and consistent with a negative (positive) phase of the NAO when the north tropical Atlantic is anomalously warm (cold). Lastly, the magnitude of the SLPA patterns over the NAE sector appears poorly related to the intensity of sea‐surface temperature anomalies in the central and eastern equatorial Pacific. Copyright © 2003 Royal Meteorological Society

Impacts of ENSO on Snowfall Frequencies in the United States

Abstract Changes in the frequency of occurrence of snowfall during El Nino–Southern Oscillation (ENSO) events are presented for the continental United States. This study is motivated by the need to improve winter climate forecasts for government agencies (i.e., U.S. Department of Transportation and Department of Energy) and winter entertainment facilities and the need for climatological studies. Daily snowfall data from 442 stations in the U.S. Historical Climatology Network are utilized. Selected stations each have more than 20 yr with 15 or more snowfall events per year during a 97-yr (1900–97) period of study. Three categories are created for each ENSO phase, based on the magnitude of daily snowfall amounts (in millimeters)—light: (0–50.8], moderate: (50.8–152.4], and heavy: (152.4–304.8]. Differences between neutral and cold or warm ENSO winters are created to show regions with increased or decreased occurrences in each snowfall category. Statistical tests are applied at each station to provide confid...

Episodic colonization of an intertidal mudflat by native cordgrass (Spartina foliosa) at Tijuana Estuary

Following heavy winter storms and sedimentation in 1993,Spartina foliosa (Pacific cordgrass) clones established on a 6.5-ha mudflat in Tijuana Estuary, with over 80 new clones counted by 1997. El Nino Southern Oscillation (ENSO) storms in 1993 apparently facilitated the habitat conversion through river flooding, which caused a temporary reduction in soil salinity and delivered large volumes of sediment. Extreme sedimentation likely raised mudflat elevations enough to allowSpartina establishment. We hypothesized that clones, once established, increased sedimentation in a positive feedback loop leading to accelerated habitat conversion. We collected data on elevation,Spartina expansion, and sediment accretion in two consecutive years (1998–1999). The elevation range of the mudflats in 1998 (0.5–0.83 m NGVD) was within the elevation range ofSpartina at this site (0.39–0.83 m NGVD), indicating that remaining mudflats are at elevations suitable for further expansion. Sediment accretion ranged from 4.0–12.7 cm between 1997–1998 (ENSO conditions), but was close to long-term averages (˜ cm yr−1) in 1998–1999 (nonflood year) indicating how susceptible Tijuana Estuary is to sedimentation from episodic storms. Although accretion rates were similar withinSpartina clones and on bare mudflats over the ENSO winter, clones were typically dome-shaped suggesting higher sediment retention rates within clones. The radial expansion rates of clones (1.31±0.25 m in 1998; 1.12±0.07 m in 1999) approximated the maxima reported for this species and were not related to clone size or vigor. Conditions on the mudflat appear ideal forSpartina growth, masking differences that might otherwise be observed. Given the likelihood of sedimentation-driven habitat conversion in southern California and other Mediterranean-type estuaries, management efforts are needed to address sedimentation issues on a watershed scale. We recommend that wetland restoration projects in southern California include large areas of intertidal mudflat, both to maintain habitat for shorebird feeding and to allow colonization by salt marsh vegetation.

Winter severity in the Great Lakes region: a tale of two oscillations

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 24:19-31 (2003) - doi:10.3354/cr024019 Winter severity in the Great Lakes region: a tale of two oscillations Sergei Rodionov1, Raymond A. Assel2,* 1Department of Computer Science, Campus Box 430, University of Colorado, Boulder, Colorado 80309-0430, USA 2National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan 48105-2945, USA *Corresponding author. Email: assel@glerl.noaa.gov ABSTRACT: The effects of Pacific Decadal Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO) on Laurentian Great Lakes regional winter air temperature and, more generally, surface-air temperatures (SAT) over North America are examined. The relationship between ENSO and winter severity in the Great Lakes is highly nonlinear and depends on the strength of El Niño events. Significant positive correlation between the winter severity and ENSO indices noted in earlier works is limited to strong El Niño events and is associated with an expansion of positive temperature anomalies in NW North America inland toward the Great Lakes. Although both ENSO and PDO are positively correlated with the Pacific-North American (PNA) teleconnection index, a closer look at the large-scale atmospheric circulation associated with the 2 oscillations reveals a substantial difference. During warm PDO phases (not coincident with strong El Niño events), atmospheric circulation resembles the classical PNA pattern, with a strong Aleutian Low at the surface and amplified ridges and troughs in the mid-troposphere. During strong El Niño events the Aleutian Low is also stronger than normal, but shifted eastward, to the Gulf of Alaska. Over North America, an upper atmospheric ridge on the west is not accompanied with a deep trough on the east as in the classical PNA pattern. As a result, outbreaks of cold Arctic air over the eastern US are rare and winters in the Great Lakes region are abnormally mild. KEY WORDS: Great Lakes · Pacific Decadal Oscillation · El Niño-Southern Oscillation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 24, No. 1. Online publication date: June 10, 2003 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2003 Inter-Research.

Analysis of Four Macroalgal Assemblages along the Pacific Mexican Coast during and after the 1997-98 El Niño

We examined the changes in four intertidal macroalgal assemblages sampled at 3-month intervals during and after the 1997–98 El Nino. The assemblages were analyzed using several numerical analyses (specific richness, H′ diversity) and multivariate techniques (ANOSIM, cluster, and MDS analyses). During El Nino 1997–98, the water temperature in the sampled zone was almost 5°C above the long-term mean. The apparent impact of this factor was greatest in winter–spring 1998. Our results suggest that El Nino influenced the structure of these assemblages in four different ways: (a) El Nino was associated with number of species (lowest in 1998) and H′ diversity, which increased in the winter of 1999, when the El Nino–Southern Oscillation (ENSO) was inactive, from 1.2 to 2.3. (b) The average biomass of the macroalgae was significantly greater in the ENSO year (139 g dry weight/m2) than in the non-ENSO year (42 g dry weight/m2) (c) El Nino conditions were associated with a high population abundance of species of tropical affinity, such as Agardhiella tenera (22.05 g dry weight/m2 in 1998 versus 0.7 g dry weight/m2 in 1999), Amphiroa misakiensis (32 versus 1.1), Caulerpa sertularoides (15.35 versus 0), Padina durvillaei (9.2 versus 0.2), Jania capillacea (4.1 versus 0), and Jania mexicana (1.5 versus 0). In 1999, other species with a more temperate affinity appeared, such as Laurencia pacifica (0.12 versus 8.76 g/m2) and Colpomenia sinuosa (0 versus 4.8). (d) The multivariate techniques showed that differences among the structure of the four assemblages were more evident in 1999. The greatest homogeneity was detected during ENSO winter–spring, which suggests a communitywide change consistent with the El Nino event.

Spatiotemporal Variability of ENSO and SST Teleconnections to Summer Drought over the United States during the Twentieth Century

Abstract Presented are investigations into the spatial structure of teleconnections between both the winter El Nino–Southern Oscillation (ENSO) and global sea surface temperatures (SSTs), and a measure of continental U.S. summer drought during the twentieth century. Potential nonlinearities and nonstationarities in the relationships are noted. During the first three decades of this century, summer drought teleconnections in response to SST patterns linked to ENSO are found to be strongest in the southern regions of Texas, with extensions into regions of the Midwest. From the 1930s through the 1950s, the drought teleconnection pattern is found to extend into southern Arizona. The most recent three decades show weak teleconnections between summer drought over southern Texas and Arizona, and winter SSTs, which is consistent with previous findings. Instead, the response to Pacific SSTs shows a clear shift to the western United States and southern regions of California. These epochal variations are consistent ...

Extreme Precipitation Events in the Western United States Related to Tropical Forcing

Abstract Three-day accumulations of precipitation for 2.5° long × 2.0° lat areas along the west coast of the United States are used to rank precipitation events. Extreme precipitation events (those above the 90th percentile) occur at all phases of the El Nino–Southern Oscillation (ENSO) cycle, but the largest fraction of these events (for the West Coast as a whole) occur during neutral winters just prior to the onset of El Nino. In the tropical Pacific these winters are characterized by enhanced activity on intraseasonal (roughly 20–60 day) timescales and by relatively small sea surface temperature anomalies compared to ENSO winters. For these winters, lagged composites are used to document a coherent relationship between the location of extreme precipitation events along the West Coast and the location of enhanced tropical convection on intraseasonal timescales. The evolution of the atmospheric circulation patterns associated with the extreme precipitation events is described and a physical mechanism rel...

Interactions with a Weather-Sensitive Decision Maker: A Case Study Incorporating ENSO Information into a Strategy for Purchasing Natural Gas

During the 1997/98 El Nino event, a Northern Illinois University (NIU) faculty member and a group of undergraduate meteorology students interacted with the university's heating plant manager to determine whether climate information and forecast tools could assist him with NIU's natural gas purchase decisions each fall. Based on the El Nino-driven temperature forecasts and information developed by the faculty-directed student group, which indicated that northern Illinois would experience a warmer than average winter (December through March), the manager chose the option to ride the market on a continuous basis, buying incrementally to reduce total natural gas expenditures, rather than lock into a fixed price. To aid this annual decision process, winter El Nino–Southern Oscillation (ENSO) classifications, based on sea surface temperature (SST) data measured in the Nino-3 region, were analyzed to determine whether relationships existed between local mean winter temperature and the ENSO phenomena during the 1...

Using Equatorial Pacific Sea Surface Temperature Anomalies to Forecast Seasonal Energy Demand in Four U.S. Regions: An Applied Climate Research Experience for Undergraduate Meteorology Students

The El Niño-Southern Oscillation (ENSO) phenomenon explains some of the interannual climate variability in many tropical and midlatitude regions. It is important in developing more accurate seasonal climate forecasts and thus in aiding long-range weather-sensitive decision making in various sectors. The degree to which ENSO information could forecast one of three classes of seasonal cooling degree days (CDD) and heating degree days (HDD) was examined using 1) the magnitude of the ENSO event during a given season, 2) the preseason rate of change of sea surface temperature (SSTs) (December–May for summers and June–October for winters), and 3) the effects of strong winter ENSO events on future seasons. All three ENSO-related indices were based on monthly equatorial Pacific SST anomalies in the Niño-3.4 region. Regional probabilities of each HDD/CDD category (above, average, and below) were determined for each ENSO predictive index. The highest probability of experiencing an HDD/CDD anomaly occurs with strong preseason SST trends. When presummer SST cooling occurs, the northeast and midcontinent experience above-average CDD (80% and 75%, respectively). Other interesting relationships were found between strong winter ENSO events and ensuing HDD/CDD anomalies. These results suggest that utility-based decision makers who can utilize enhanced climate information may reap benefits during particular years by integrating the ENSO information into their models. This study was part of a special student training experiment conducted at Northern Illinois University.

ENSO variability and atmospheric response in a global coupled atmosphere-ocean GCM

The interannual variability associated with the El Nino/Southern Oscillation (ENSO) cycle is investigated using a relatively high-resolution (T42) coupled general circulation model (CGCM) of the atmosphere and ocean. Although the flux correction is restricted to annual means of heat and freshwater, the annual as well as the seasonal climate of the CGCM is in good agreement with that of the atmospheric model component forced with observed sea surface temperatures (SSTs). During a 100-year simulation of the present-day climate, the model is able to capture many features of the observed interannual SST variability in the tropical Pacific. This includes amplitude, lifetime and frequency of occurrence of El Nino events and also the phase locking of the SST anomalies to the annual cycle. Although the SST warming during the evolution of El Ninos is too confined spatially, and the warming along the Peruvian coast is much too weak, the patterns and magnitudes of key atmospheric anomalies such as westerly wind stress and precipitation, and also their eastward migration from the western to the central equatorial Pacific is in accord with observations. There is also a qualitative agreement with the results obtained from the atmospheric model forced with observed SSTs from 1979 through 1994. The large-scale dynamic response during the mature phase of ENSO (December through February) is characterized by an eastward displacement and weakening of the Walker cell in the Pacific while the Hadley cell intensifies and moves equatorward. Similar to the observations, there is a positive correlation between tropical Pacific SST and the winter circulation in the North Pacific. The deepening of the Aleutian low during the ENSO winters is well captured by the model as well as the cooling in the central North Pacific and the warming over Canada and Alaska. However, there are indications that the anomalies of both SST and atmospheric circulation are overemphasized in the North Pacific. Finally, there is evidence of a coherent downstream effect over the North Atlantic as indicated by negative correlations between the PNA index and the NAO index, for example. The weakening of the westerlies across the North Atlantic in ENSO winters which is related to a weakening and southwestward displacement of the Icelandic low, is in broad agreement with the observations, as well as the weak tendency for colder than normal winters in Europe.

INFLUENCE OF EL NINOS ON CALIFORNIA'S WAVE CLIMATE

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.