scholarly journals Contributions from California Coastal-Zone Surface Fluxes to Heavy Coastal Precipitation: A CALJET Case Study during the Strong El Niño of 1998

2005 ◽  
Vol 133 (5) ◽  
pp. 1175-1198 ◽  
Author(s):  
P. Ola G. Persson ◽  
P. J. Neiman ◽  
B. Walter ◽  
J-W. Bao ◽  
F. M. Ralph
Keyword(s):  
Boundary Layer ◽  
Latent Heat ◽  
El Niño ◽  
Model Simulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Surface Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sst Anomalies

Abstract Analysis of the case of 3 February 1998, using an extensive observational system in the California Bight during an El Niño winter, has revealed that surface sensible and latent heat fluxes within 150 km of the shore contributed substantially to the destabilization of air that subsequently produced strong convection and flooding along the coast. Aircraft, dropsonde, and satellite observations gathered offshore documented the sea surface temperatures (SSTs), surface fluxes, stratification, and frontal structures. These were used to extrapolate the effects of the fluxes on the warm-sector, boundary layer air ahead of a secondary cold front as this air moved toward the coast. The extrapolated structure was then validated in detail with nearshore aircraft, wind profiler, sounding, and buoy observations of the frontal convection along the coast, and the trajectory transformations were confirmed with a model simulation. The results show that the surface fluxes increased CAPE by about 26% such that the nearshore boundary layer values of 491 J kg−1 were near the upper end of those observed for cool-season California thunderstorms. The increased CAPE due to upward sensible and latent heat fluxes was a result of the anomalously warm coastal SSTs (+1°–3°C) typical of strong El Niño events. Applications of the extrapolation method using a surface flux parameterization scheme and different SSTs suggested that convective destabilization due to nearshore surface fluxes may only occur during El Niño years when positive coastal SST anomalies are present. The fluxes may have no effect or a stabilizing effect during non–El Niño years, characterized by zero or negative coastal SST anomalies. In short, during strong El Niños, it appears that the associated coastal SST anomalies serve to further intensify the already anomalously strong storms in southern California, thus contributing to the increased flooding. This modulating effect by El Niño–Southern Oscillation (ENSO) of a mesoscale process has not been considered before in attempts at assessing the impacts of ENSO on U.S. west coast precipitation.

scholarly journals Properties of El Niño–Southern Oscillation in Different Equilibrium Climates with HadCM3

2006 ◽  
Vol 19 (19) ◽  
pp. 4854-4876 ◽  
Author(s):  
Thomas Toniazzo
Keyword(s):  
Wind Stress ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Surface Flux ◽  
Co2 Concentration ◽  
Climatic Conditions ◽  
Stable Steady State ◽  
Sst Variability ◽  
Sst Anomalies

Abstract The ENSO variability in three long, stable, steady-state integrations of the Third Hadley Centre Coupled Ocean–Atmosphere GCM (HadCM3) is analyzed, relevant to climatic conditions of the Last Glacial Maximum (LGM), of the preindustrial period [control (CTL)], and of a greenhouse stabilization scenario (GHS) at 4 times the preindustrial CO2 concentration. It is found that progressively from LGM to CTL and GHS, the SST variability pattern associated with ENSO is centered farther west, and the oscillation acquires a shorter dominant period. While there are no large changes in total SST variability, very strong events become less frequent, and El Niño events develop over a narrower period within the seasonal cycle. The westward ENSO pattern shift is concurrent with a similar shift in the climatological wind stress distribution and with increased convective activity over the west equatorial Pacific. The wind response to anomalous SSTs follows this shift and increases in strength. The thermocline feedback becomes stronger in the 4 × CO2 integration, but the largest SST anomalies are associated with surface processes. The role of surface flux damping for the decay of anomalous SSTs is reduced in LGM and increased in GHS. From the analysis, the principal changes in mean climate that appear to affect the evolution of ENSO-related SST anomalies in HadCM3 are thus the changes in zonal wind stress over the equator, the depth of the equatorial thermocline, and the sensitivity of atmospheric convection to equatorial SST anomalies.

scholarly journals Role of the Indo-Pacific Interbasin Coupling in Predicting Asymmetric ENSO Transition and Duration

2012 ◽  
Vol 25 (9) ◽  
pp. 3321-3335 ◽  
Author(s):  
Masamichi Ohba ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
La Nina ◽  
The Pacific ◽  
Enso Asymmetry ◽  
Sst Anomalies

Warm and cold phases of El Niño–Southern Oscillation (ENSO) exhibit a significant asymmetry in their transition/duration such that El Niño tends to shift rapidly to La Niña after the mature phase, whereas La Niña tends to persist for up to 2 yr. The possible role of sea surface temperature (SST) anomalies in the Indian Ocean (IO) in this ENSO asymmetry is investigated using a coupled general circulation model (CGCM). Decoupled-IO experiments are conducted to assess asymmetric IO feedbacks to the ongoing ENSO evolution in the Pacific. Identical-twin forecast experiments show that a coupling of the IO extends the skillful prediction of the ENSO warm phase by about one year, which was about 8 months in the absence of the IO coupling, in which a significant drop of the prediction skill around the boreal spring (known as the spring prediction barrier) is found. The effect of IO coupling on the predictability of the Pacific SST is significantly weaker in the decay phase of La Niña. Warm IO SST anomalies associated with El Niño enhance surface easterlies over the equatorial western Pacific and hence facilitate the El Niño decay. However, this mechanism cannot be applied to cold IO SST anomalies during La Niña. The result of these CGCM experiments estimates that approximately one-half of the ENSO asymmetry arises from the phase-dependent nature of the Indo-Pacific interbasin coupling.

scholarly journals ENSO’s Impact on the Gap Wind Regions of the Eastern Tropical Pacific Ocean*

2012 ◽  
Vol 25 (10) ◽  
pp. 3549-3565 ◽  
Author(s):  
Michael A. Alexander ◽  
Hyodae Seo ◽  
Shang Ping Xie ◽  
James D. Scott
Keyword(s):  
Pacific Ocean ◽  
Boundary Conditions ◽  
El Niño ◽  
El Nino ◽  
Tropical Pacific ◽  
Surface Fluxes ◽  
Ocean Dynamics ◽  
Tropical Pacific Ocean ◽  
Variable Surface ◽  
Sst Anomalies

Abstract The recently released NCEP Climate Forecast System Reanalysis (CFSR) is used to examine the response to ENSO in the northeast tropical Pacific Ocean (NETP) during 1979–2009. The normally cool Pacific sea surface temperatures (SSTs) associated with wind jets through the gaps in the Central American mountains at Tehuantepec, Papagayo, and Panama are substantially warmer (colder) than the surrounding ocean during El Niño (La Niña) events. Ocean dynamics generate the ENSO-related SST anomalies in the gap wind regions as the surface fluxes damp the SSTs anomalies, while the Ekman heat transport is generally in quadrature with the anomalies. The ENSO-driven warming is associated with large-scale deepening of the thermocline; with the cold thermocline water at greater depths during El Niño in the NETP, it is less likely to be vertically mixed to the surface, particularly in the gap wind regions where the thermocline is normally very close to the surface. The thermocline deepening is enhanced to the south of the Costa Rica Dome in the Papagayo region, which contributes to the local ENSO-driven SST anomalies. The NETP thermocline changes are due to coastal Kelvin waves that initiate westward-propagating Rossby waves, and possibly ocean eddies, rather than by local Ekman pumping. These findings were confirmed with regional ocean model experiments: only integrations that included interannually varying ocean boundary conditions were able to simulate the thermocline deepening and localized warming in the NETP during El Niño events; the simulation with variable surface fluxes, but boundary conditions that repeated the seasonal cycle, did not.

scholarly journals Indo-Western Pacific Climate Variability: ENSO Forcing and Internal Dynamics in a Tropical Pacific Pacemaker Simulation

2018 ◽  
Vol 31 (24) ◽  
pp. 10123-10139 ◽  
Author(s):  
Chuan-Yang Wang ◽  
Shang-Ping Xie ◽  
Yu Kosaka
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Internal Variability ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Ocean Atmosphere ◽  
Sst Anomalies

El Niño–Southern Oscillation (ENSO) peaks in boreal winter but its impact on Indo-western Pacific climate persists for another two seasons. Key ocean–atmosphere interaction processes for the ENSO effect are investigated using the Pacific Ocean–Global Atmosphere (POGA) experiment with a coupled general circulation model, where tropical Pacific sea surface temperature (SST) anomalies are restored to follow observations while the atmosphere and oceans are fully coupled elsewhere. The POGA shows skills in simulating the ENSO-forced warming of the tropical Indian Ocean and an anomalous anticyclonic circulation pattern over the northwestern tropical Pacific in the post–El Niño spring and summer. The 10-member POGA ensemble allows decomposing Indo-western Pacific variability into the ENSO forced and ENSO-unrelated (internal) components. Internal variability is comparable to the ENSO forcing in magnitude and independent of ENSO amplitude and phase. Random internal variability causes apparent decadal modulations of ENSO correlations over the Indo-western Pacific, which are high during epochs of high ENSO variance. This is broadly consistent with instrumental observations over the past 130 years as documented in recent studies. Internal variability features a sea level pressure pattern that extends into the north Indian Ocean and is associated with coherent SST anomalies from the Arabian Sea to the western Pacific, suggestive of ocean–atmosphere coupling.

Subcloud and Cloud-Base Latent Heat Fluxes during Shallow Cumulus Convection

2019 ◽  
Vol 77 (3) ◽  
pp. 1081-1100 ◽  
Author(s):  
Neil P. Lareau
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Latent Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Cloud Base ◽  
Cumulus Convection ◽  
Mixing Ratio ◽  
Convective Boundary ◽  
Water Vapor Mixing Ratio

Abstract Doppler and Raman lidar observations of vertical velocity and water vapor mixing ratio are used to probe the physics and statistics of subcloud and cloud-base latent heat fluxes during cumulus convection at the ARM Southern Great Plains (SGP) site in Oklahoma, United States. The statistical results show that latent heat fluxes increase with height from the surface up to ~0.8Zi (where Zi is the convective boundary layer depth) and then decrease to ~0 at Zi. Peak fluxes aloft exceeding 500 W m−2 are associated with periods of increased cumulus cloud cover and stronger jumps in the mean humidity profile. These entrainment fluxes are much larger than the surface fluxes, indicating substantial drying over the 0–0.8Zi layer accompanied by moistening aloft as the CBL deepens over the diurnal cycle. We also show that the boundary layer humidity budget is approximately closed by computing the flux divergence across the 0–0.8Zi layer. Composite subcloud velocity and water vapor anomalies show that clouds are linked to coherent updraft and moisture plumes. The moisture anomaly is Gaussian, most pronounced above 0.8Zi and systematically wider than the velocity anomaly, which has a narrow central updraft flanked by downdrafts. This size and shape disparity results in downdrafts characterized by a high water vapor mixing ratio and thus a broad joint probability density function (JPDF) of velocity and mixing ratio in the upper CBL. We also show that cloud-base latent heat fluxes can be both positive and negative and that the instantaneous positive fluxes can be very large (~10 000 W m−2). However, since cloud fraction tends to be small, the net impact of these fluxes remains modest.

scholarly journals Combined Impact of El Niño–Southern Oscillation and Pacific Decadal Oscillation on the Northern Winter Stratosphere

Atmosphere ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 211 ◽  
Author(s):  
Jian Rao ◽  
Rongcai Ren ◽  
Xin Xia ◽  
Chunhua Shi ◽  
Dong Guo
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
La Niña ◽  
Stratospheric Polar Vortex ◽  
The North ◽  
La Nina ◽  
Sst Anomalies

Using reanalysis and the sea surface temperature (SST) analysis, the combined impact of El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on the northern winter stratosphere is investigated. The warm and weak stratospheric polar vortex response to El Niño simply appears during positive PDO, whereas the cold and strong stratospheric polar vortex response to La Niña is preferable during negative PDO in the reanalysis. Two mechanisms may account for the enhanced stratospheric response when ENSO and PDO are in phase. First, the asymmetries of the intensity and frequency between El Niño and La Niña can be identified for the two PDO phases. Second, the extratropical SST anomalies in the North Pacific may also play a role in the varying extratropical response to ENSO. The North Pacific SST anomalies related to PDO superimpose ENSO SST anomalies when they are in phase but undermine them when they are out of phase. The superimposed North Pacific SST anomalies help to increase SST meridional gradient anomalies between tropical and extratropics, as well as to lock the local height response to ENSO. Therefore, the passages for the upward propagation of waves from the troposphere is more unimpeded when positive PDO is configured with El Niño, and vice versa when negative PDO is configured with La Niña.

scholarly journals Hemispheric transport and influence of meteorology on global aerosol climatology

2012 ◽  
Vol 12 (16) ◽  
pp. 7609-7624 ◽  
Author(s):  
T. L. Zhao ◽  
S. L. Gong ◽  
P. Huang ◽  
D. Lavoué
Keyword(s):  
Boundary Layer ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Late Summer ◽  
Late Winter ◽  
Aerosol Transport ◽  
Transport Pathways ◽  
Annual Variations ◽  
Annual Variability

Abstract. Based on a 10-yr simulation with the global air quality modeling system GEM-AQ/EC, the northern hemispheric aerosol transport with the inter-annual and seasonal variability as well as the mean climate was investigated. The intercontinental aerosol transport is predominant in the zonal direction from west to east with the ranges of inter-annual variability between 14% and 63%, and is 0.5–2 orders of magnitude weaker in the meridional direction but with larger inter-annual variability. The aerosol transport is found to fluctuate seasonally with a factor of 5–8 between the maximum in late winter and spring and the minimum in late summer and fall. Three meteorological factors controlling the intercontinental aerosol transport and its inter-annual variations are identified from the modeling results: (1) Anomalies in the mid-latitude westerlies in the troposphere. (2) Variations of precipitation over the intercontinental transport pathways and (3) Changes of meteorological conditions within the boundary layer. Changed only by the meteorology, the aerosol column loadings in the free troposphere over the source regions of Europe, North America, South and East Asia vary inter-annually with the highest magnitudes of 30–37% in January and December and the lowest magnitudes of 16–20% in August and September, and the inter-annual aerosol variability within the boundary layer influencing the surface concentrations with the magnitudes from 6% to 20% is more region-dependent. As the strongest climatic signal, the El Niño-Southern Oscillation (ENSO) can lead the anomalies in the intercontinental aerosols in El Niño- and La Niña-years respectively with the strong and weak transport of the mid-latitude westerlies and the low latitude easterlies in the Northern Hemisphere (NH).

scholarly journals An Asymmetry in the IOD and ENSO Teleconnection Pathway and Its Impact on Australian Climate

2012 ◽  
Vol 25 (18) ◽  
pp. 6318-6329 ◽  
Author(s):  
Wenju Cai ◽  
Peter van Rensch ◽  
Tim Cowan ◽  
Harry H. Hendon
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Austral Spring ◽  
Southeast Australia ◽  
Unit Change ◽  
The Impact ◽  
Sst Anomalies

Abstract Recent research has shown that the climatic impact from El Niño–Southern Oscillation (ENSO) on middle latitudes west of the western Pacific (e.g., southeast Australia) during austral spring (September–November) is conducted via the tropical Indian Ocean (TIO). However, it is not clear whether this impact pathway is symmetric about the positive and negative phases of ENSO and the Indian Ocean dipole (IOD). It is shown that a strong asymmetry does exist. For ENSO, only the impact from El Niño is conducted through the TIO pathway; the impact from La Niña is delivered through the Pacific–South America pattern. For the IOD, a greater convection anomaly and wave train response occurs during positive IOD (pIOD) events than during negative IOD (nIOD) events. This “impact asymmetry” is consistent with the positive skewness of the IOD, principally due to a negative skewness of sea surface temperature (SST) anomalies in the east IOD (IODE) pole. In the IODE region, convection anomalies are more sensitive to a per unit change of cold SST anomalies than to the same unit change of warm SST anomalies. This study shows that the IOD skewness occurs despite the greater damping, rather than due to a breakdown of this damping as suggested by previous studies. This IOD impact asymmetry provides an explanation for much of the reduction in spring rainfall over southeast Australia during the 2000s. Key to this rainfall reduction is the increased occurrences of pIOD events, more so than the lack of nIOD events.

scholarly journals Maximizing ENSO as a source of western US hydroclimate predictability

2019 ◽  
Vol 54 (1-2) ◽  
pp. 351-372 ◽  
Author(s):  
Christina M. Patricola ◽  
John P. O’Brien ◽  
Mark D. Risser ◽  
Alan M. Rhoades ◽  
Travis A. O’Brien ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Global Climate Model ◽  
Western Us ◽  
El Niño Events ◽  
Fixed Region ◽  
Sst Anomalies ◽  
El Nino Events

Abstract Until recently, the El Niño–Southern Oscillation (ENSO) was considered a reliable source of winter precipitation predictability in the western US, with a historically strong link between extreme El Niño events and extremely wet seasons. However, the 2015–2016 El Niño challenged our understanding of the ENSO-precipitation relationship. California precipitation was near-average during the 2015–2016 El Niño, which was characterized by warm sea surface temperature (SST) anomalies of similar magnitude compared to the extreme 1997–1998 and 1982–1983 El Niño events. We demonstrate that this precipitation response can be explained by El Niño’s spatial pattern, rather than internal atmospheric variability. In addition, observations and large-ensembles of regional and global climate model simulations indicate that extremes in seasonal and daily precipitation during strong El Niño events are better explained using the ENSO Longitude Index (ELI), which captures the diversity of ENSO’s spatial patterns in a single metric, compared to the traditional Niño3.4 index, which measures SST anomalies in a fixed region and therefore fails to capture ENSO diversity. The physically-based ELI better explains western US precipitation variability because it tracks the zonal shifts in tropical Pacific deep convection that drive teleconnections through the response in the extratropical wave-train, integrated vapor transport, and atmospheric rivers. This research provides evidence that ELI improves the value of ENSO as a predictor of California’s seasonal hydroclimate extremes compared to traditional ENSO indices, especially during strong El Niño events.

scholarly journals On the influences of the El Niño, La niña and Atlantic Dipole Paterni on the Amazonian Rainfall during 1960-1998

2000 ◽  
Vol 30 (2) ◽  
pp. 305-318 ◽  
Author(s):  
Everaldo B de SOUZA ◽  
Mary T KAYANO ◽  
Julio TOTA ◽  
Luciano PEZZI ◽  
Gilberto FISCH ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Austral Summer ◽  
La Niña ◽  
Tropical Atlantic ◽  
La Nina ◽  
Precipitation Anomalies ◽  
Dipole Pattern ◽  
Sst Anomalies

The influence of the large-scale climatic variability dominant modes in the Pacific and in the Atlantic on Amazonian rainfall is investigated. The composite technique of the Amazon precipitation anomalies is used in this work. The basis years for these composites arc those in the period 1960-1998 with occurrences of extremes in the Southern Oscillation (El Niño or La Niña) and the north/south warm (or cold) sea surface temperature (SST) anomalies dipole pattern in the tropical Atlantic. Warm (cold) dipole means positive (negative) anomalies in the tropical North Atlantic and negative (positive) anomalies in the tropical South Atlantic. Austral summer and autumn composites for extremes in the Southern Oscillation (El Niño or La Niña) and independently for north/south dipole pattern (warm or cold) of the SST anomalies in the tropical Atlantic present values (magnitude and sign) consistent with those found in previous works on the relationship between Amazon rainfall variations and the SST anomalies in the tropical Pacific and Atlantic. However, austral summer and autumn composites for the years with simultaneous occurrences of El Niño and warm north/south dipole of the SST anomalies in the tropical Atlantic show negative precipitation anomalies extending eastward over the center-eastern Amazon. This result indicates the important role played by the tropical Atlantic in the Amazon anomalous rainfall distribution.

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