A Lagged Warm Event–Like Response to Peaks in Solar Forcing in the Pacific Region

2009 ◽  
Vol 22 (13) ◽  
pp. 3647-3660 ◽  
Author(s):  
Gerald A. Meehl ◽  
Julie M. Arblaster
Keyword(s):  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
Forced Response ◽  
Pacific Region ◽  
Solar Forcing ◽  
Cold Event ◽  
Warm Event ◽  
The Pacific ◽  
The Tropical Pacific

Abstract The forced response coincident with peaks in the 11-yr decadal solar oscillation (DSO) has been shown to resemble a cold event or La Niña–like pattern during December–February (DJF) in the Pacific region in observations and two global coupled climate models. Previous studies with filtered observational and model data have indicated that there could be a lagged warm event or El Niño–like response following the peaks in the DSO forcing by a few years. Here, observations and two climate model simulations are examined, and it is shown that dynamical coupled processes initiated by the response in the tropical Pacific to peaks in solar forcing produce wind-forced ocean Rossby waves near 5°N and 5°S. These reflect off the western boundary, producing downwelling equatorial Kelvin waves that contribute to transitioning the tropical Pacific to a warm event or El Niño–like pattern that lags the peaks in solar forcing by a few years.

Impacts of El Niño-Southern Oscillation on Natural and Human Systems

2007 ◽  
Author(s):  
César N. Caviedes
Keyword(s):  
El Niño ◽  
Wind Shear ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Tropical Species ◽  
Humboldt Current ◽  
The Pacific ◽  
Gulf Of Guayaquil ◽  
The Tropical Pacific

Off the coasts of northern Perú and southern Ecuador, warm equatorial waters meet the cold Humboldt Current. Variations in sea temperatures and associated fauna have been known to fishing folk since colonial times. They noticed that toward the end of every year tepid waters appeared between the Gulf of Guayaquil (Ecuador) and Point Pariñas (Perú) and persisted until late February, causing tropical species to be added to the fish they commonly caught. Coupled with the arrival of warm waters was a surge in air humidity and an increase in summer showers. Since this environmental phenomenon occurred around Christmas, the local fishermen called it El Niño, or Child Jesus. Early scientific observations on the nature and extent of these phenomena revealed that they were not regionally restricted to coastal Perú and Ecuador, but extended over the whole tropical Pacific, involving pressure fields and wind flows across the basin. Thus, when referring to this coupled ocean-atmospheric system, both variations of sea temperature across the tropical Pacific and changes of the atmosphere in contact with the ocean must be considered (Neelin et al., 1998). Normally, the tropical Pacific Ocean, from the coast of Ecuador and Perú to longitude 120°W, is dominated by westward- flowing cold waters, which are the prolongation of the Humboldt Current. Near longitude 120°W, sea surface temperatures approach normal equatorial values of ~28°C. When the flow reaches the western Pacific, it creates a sealevel rise of nearly 40 cm, which is maintained by the wind shear of the equatorial easterlies. The thermocline, which marks the lower boundary of the sun-heated water layer, runs at a depth of 40 m between Perú and the Galápagos Islands, but on the Asian side of the Pacific it dips to 120 m, revealing a marked asymmetry in the thickness of the sunheated layer across the Pacific. During El Niño years, the westward flow of cooler waters is weak because there is less wind shear from the easterly winds, and the thermocline plunges to 80 m in the eastern equatorial Pacific.

scholarly journals A Coupled Air–Sea Response Mechanism to Solar Forcing in the Pacific Region

2008 ◽  
Vol 21 (12) ◽  
pp. 2883-2897 ◽  
Author(s):  
Gerald A. Meehl ◽  
Julie M. Arblaster ◽  
Grant Branstator ◽  
Harry van Loon
Keyword(s):  
Climate Model ◽  
Tropical Pacific ◽  
South Pacific Convergence Zone ◽  
Convergence Zone ◽  
Pacific Region ◽  
Solar Forcing ◽  
Coupled Models ◽  
The Pacific ◽  
Precipitation Regimes ◽  
The Tropical Pacific

Abstract The 11-yr solar cycle [decadal solar oscillation (DSO)] at its peaks strengthens the climatological precipitation maxima in the tropical Pacific during northern winter. Results from two global coupled climate model ensemble simulations of twentieth-century climate that include anthropogenic (greenhouse gases, ozone, and sulfate aerosols, as well as black carbon aerosols in one of the models) and natural (volcano and solar) forcings agree with observations in the Pacific region, though the amplitude of the response in the models is about half the magnitude of the observations. These models have poorly resolved stratospheres and no 11-yr ozone variations, so the mechanism depends almost entirely on the increased solar forcing at peaks in the DSO acting on the ocean surface in clear sky areas of the equatorial and subtropical Pacific. Mainly due to geometrical considerations and cloud feedbacks, this solar forcing can be nearly an order of magnitude greater in those regions than the globally averaged solar forcing. The mechanism involves the increased solar forcing at the surface being manifested by increased latent heat flux and evaporation. The resulting moisture is carried to the convergence zones by the trade winds, thereby strengthening the intertropical convergence zone (ITCZ) and the South Pacific convergence zone (SPCZ). Once these precipitation regimes begin to intensify, an amplifying set of coupled feedbacks similar to that in cold events (or La Niña events) occurs. There is a strengthening of the trades and greater upwelling of colder water that extends the equatorial cold tongue farther west and reduces precipitation across the equatorial Pacific, while increasing precipitation even more in the ITCZ and SPCZ. Experiments with the atmosphere component from one of the coupled models are performed in which heating anomalies similar to those observed during DSO peaks are specified in the tropical Pacific. The result is an anomalous Rossby wave response in the atmosphere and consequent positive sea level pressure (SLP) anomalies in the North Pacific extending to western North America. These patterns match features that occur during DSO peak years in observations and the coupled models.

Winter freezes of fruit trees in the Okanagan Valley, British Columbia: Relationship with the Pacific North America teleconnection and the El Nino/Southern Oscillation

1994 ◽  
Vol 74 (4) ◽  
pp. 841-846 ◽  
Author(s):  
J. W. Hall ◽  
H. A. Quamme
Keyword(s):  
North America ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Cold Event ◽  
Warm Event ◽  
The Pacific ◽  
Okanagan Valley

Every 5–7 years there are severe winter freezes in the Okanagan Valley which lower yields or kill apple trees. Our goal was to determine whether winter freezes (December, January and February) could be related to the Pacific North America teleconnection (PNA) and the El Nino/Southern Oscillation (ENSO). Fall and spring freezes were also discussed. A list of ENSO warm event, cold event and neutral years was available from 1947 to 1986 as well as monthly temperature and precipitation records. Months were classified as having a PNA, reverse PNA (r-PNA) or neutral pattern. There was a tendency for the r-PNA pattern to occur more and the PNA pattern less frequently in cold event winters than in warm event winters. The average temperature was lower when the r-PNA predominated but ENSO events had no additional effect. No relationship was detected with precipitation. Fall and winter freezes occurred when there was an r-PNA pattern combined with either a neutral or a cold event ENSO. These results suggest that the risk of winter freezes will be low during ENSO warm events and high when the r-PNA pattern predominates. Key words:Malus domestica, Prunus persica, freezing injury, teleconnexions, El Nino/Southern Oscillation

scholarly journals ENSO’s Modulation of Water Vapor Transport over the Pacific–North American Region

2015 ◽  
Vol 28 (9) ◽  
pp. 3846-3856 ◽  
Author(s):  
Hye-Mi Kim ◽  
Michael A. Alexander
Keyword(s):  
United States ◽  
El Niño ◽  
North Pacific ◽  
Moisture Transport ◽  
El Nino ◽  
Tropical Pacific ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
Southwestern United States ◽  
The Pacific

Abstract The vertically integrated water vapor transport (IVT) over the Pacific–North American sector during three phases of ENSO in boreal winter (December–February) is investigated using IVT values calculated from the Climate Forecast System Reanalysis (CFSR) during 1979–2010. The shift of the location and sign of sea surface temperature (SST) anomalies in the tropical Pacific Ocean leads to different atmospheric responses and thereby changes the seasonal mean moisture transport into North America. During eastern Pacific El Niño (EPEN) events, large positive IVT anomalies extend northeastward from the subtropical Pacific into the northwestern United States following the anomalous cyclonic flow around a deeper Aleutian low, while a southward shift of the cyclonic circulation during central Pacific El Niño (CPEN) events induces the transport of moisture into the southwestern United States. In addition, moisture from the eastern tropical Pacific is transported from the deep tropical eastern Pacific into Mexico and the southwestern United States during CPEN. During La Niña (NINA), the seasonal mean IVT anomaly is opposite to that of two El Niño phases. Analyses of 6-hourly IVT anomalies indicate that there is strong moisture transport from the North Pacific into the northwestern and southwestern United States during EPEN and CPEN, respectively. The IVT is maximized on the southeastern side of a low located over the eastern North Pacific, where the low is weaker but located farther south and closer to shore during CPEN than during EPEN. Moisture enters the southwestern United States from the eastern tropical Pacific during NINA via anticyclonic circulation associated with a ridge over the southern United States.

scholarly journals Possible Impact of the Indian Ocean SST on the Northern Hemisphere Circulation during El Niño*

2007 ◽  
Vol 20 (13) ◽  
pp. 3164-3189 ◽  
Author(s):  
H. Annamalai ◽  
H. Okajima ◽  
M. Watanabe
Keyword(s):  
Indian Ocean ◽  
Northern Hemisphere ◽  
El Niño ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Tropical Pacific ◽  
The Indian Ocean ◽  
Precipitation Anomalies ◽  
Sst Anomalies ◽  
The Tropical Pacific

Abstract Two atmospheric general circulation models (AGCMs), differing in numerics and physical parameterizations, are employed to test the hypothesis that El Niño–induced sea surface temperature (SST) anomalies in the tropical Indian Ocean impact considerably the Northern Hemisphere extratropical circulation anomalies during boreal winter [January–March +1 (JFM +1)] of El Niño years. The hypothesis grew out of recent findings that ocean dynamics influence SST variations over the southwest Indian Ocean (SWIO), and these in turn impact local precipitation. A set of ensemble simulations with the AGCMs was carried out to assess the combined and individual effects of tropical Pacific and Indian Ocean SST anomalies on the extratropical circulation. To elucidate the dynamics responsible for the teleconnection, solutions were sought from a linear version of one of the AGCMs. Both AGCMs demonstrate that the observed precipitation anomalies over the SWIO are determined by local SST anomalies. Analysis of the circulation response shows that over the Pacific–North American (PNA) region, the 500-hPa height anomalies, forced by Indian Ocean SST anomalies, oppose and destructively interfere with those forced by tropical Pacific SST anomalies. The model results validated with reanalysis data show that compared to the runs where only the tropical Pacific SST anomalies are specified, the root-mean-square error of the height anomalies over the PNA region is significantly reduced in runs in which the SST anomalies in the Indian Ocean are prescribed in addition to those in the tropical Pacific. Among the ensemble members, both precipitation anomalies over the SWIO and the 500-hPa height over the PNA region show high potential predictability. The solutions from the linear model indicate that the Rossby wave packets involved in setting up the teleconnection between the SWIO and the PNA region have a propagation path that is quite different from the classical El Niño–PNA linkage. The results of idealized experiments indicate that the Northern Hemisphere extratropical response to Indian Ocean SST anomalies is significant and the effect of this response needs to be considered in understanding the PNA pattern during El Niño years. The results presented herein suggest that the tropical Indian Ocean plays an active role in climate variability and that accurate observation of SST there is of urgent need.

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