scholarly journals Formation, Mechanisms, and Predictability of the Aleutian–Icelandic Low Seesaw in Ensemble AGCM Simulations

2005 ◽  
Vol 18 (9) ◽  
pp. 1423-1434 ◽  
Author(s):  
Meiji Honda ◽  
Yochanan Kushnir ◽  
Hisashi Nakamura ◽  
Shozo Yamane ◽  
Stephen E. Zebiak
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Wave Train ◽  
Wave Activity ◽  
Potential Predictability ◽  
The North ◽  
Ensemble Mean ◽  
Internal Component ◽  
The North Atlantic ◽  
The North Pacific

Abstract The potential predictability associated with the remote influence of midlatitude tropospheric anomalies over the North Pacific or the North Atlantic, via a seesawlike interannual oscillation between the surface Aleutian and Icelandic lows (AL and IL, respectively) is investigated. Data from a 24-member ensemble of 50-yr atmospheric general circulation model simulation forced with observed sea surface temperature (SST) conditions are analyzed by separating the total simulated fluctuations into the external component forced by the prescribed SST and the internal component generated by atmospheric internal dynamics. The AL–IL seesaw can be identified in both the external and internal components of the variability. In the external variability, determined through the ensemble mean, the seesaw is gradually formed from December to March through the development of a Pacific–North American (PNA) pattern–like wave train, remotely forced by the El Niño–Southern Oscillation. The amplitudes of the externally forced North Atlantic anomalies are only about half as large as the North Pacific anomalies. The potential predictability of the Atlantic anomalies, defined as the ratio of the SST-forced variance to the total variance, does not exceed the 20% level. In the internal component of the variability, determined from the deviations of each ensemble member from the ensemble mean, the negative correlation between the AL and IL anomalies is modest but persistent through winter. It is confirmed that, regardless of the polarity of the AL–IL seesaw, the IL anomalies are formed through eastward wave activity propagation of the stationary Rossby wave train emanating from the AL region in the form of what may be called a “PNAA pattern,” the extension of the PNA-like wave train into the Atlantic. Thus, the midwinter development of North Pacific anomalies is found to be a necessary, though not sufficient, condition for the seesaw formation. The persistence of the North Pacific anomalies beyond a 1-month time span appears to augment the probability of the seesaw formation by sustaining eastward wave activity propagation to the North Atlantic.

North Hemispheric winter air temperature variability and its linkage to North Pacific and North Atlantic SST modes?

2020 ◽  
Author(s):  
Binhe Luo ◽  
Dehai Luo ◽  
Aiguo Dai ◽  
Lixin Wu
Keyword(s):  
North America ◽  
Air Temperature ◽  
North Atlantic ◽  
North Pacific ◽  
Wave Train ◽  
Surface Air Temperature ◽  
Eastern North America ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

<p>Winter surface air temperature (SAT) over North America exhibits pronounced variability on sub-seasonal-to-interdecadal timescales, but its causes are not fully understood. Here observational and reanalysis data from 1950-2017 are analyzed to investigate these causes. Detrended daily SAT data reveals a known warm-west/cold-east (WWCE) dipole over midlatitude North America and a cold-north/warm-south (CNWS) dipole over eastern North America. It is found that while the North Pacific blocking (PB) is important for the WWCE and CNWS dipoles, they also depend on the phase of the North Atlantic Oscillation (NAO). When a negative-phase NAO (NAO-) concurs with PB, the WWCE dipole is enhanced (compared with the PB alone case) and it also leads to a warm north/cold south dipole anomaly in eastern North America; but when PB occurs with a positive-phase NAO (NAO<sup>+</sup>), the WWCE dipole weakens and the CNWS dipole is enhanced. In particular, the WWCE dipole is favored by a combination of eastward-displaced PB and NAO<sup>-</sup> that form a negative Arctic Oscillation. Furthermore, a WWCE dipole can form over midlatitude North America when PB occurs together with southward-displaced NAO<sup>+</sup>.The PB events concurring with NAO<sup>-</sup> (NAO<sup>+</sup>) and SAT WWCE (CNWS) dipole are favored by the El Nio-like (La Nia-like) SST mode, though related to the North Atlantic warm-cold-warm (cold-warm-cold) SST tripole pattern. It is also found that the North Pacific mode tends to enhance the WWCE SAT dipole through increasing PB-NAO<sup>-</sup> events and producing the WWCE SAT dipole component related to the PB-NAO<sup>+</sup> events because the PB and NAO<sup>+</sup> form a more zonal wave train in this case.</p>

The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation

2020 ◽  
Vol 33 (6) ◽  
pp. 2111-2130
Author(s):  
Woo Geun Cheon ◽  
Jong-Seong Kug
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
North Pacific ◽  
Global Ocean ◽  
The North ◽  
Westerly Winds ◽  
The North Atlantic ◽  
Global Ocean Circulation ◽  
The Antarctic ◽  
The North Pacific

AbstractIn the framework of a sea ice–ocean general circulation model coupled to an energy balance atmospheric model, an intensity oscillation of Southern Hemisphere (SH) westerly winds affects the global ocean circulation via not only the buoyancy-driven teleconnection (BDT) mode but also the Ekman-driven teleconnection (EDT) mode. The BDT mode is activated by the SH air–sea ice–ocean interactions such as polynyas and oceanic convection. The ensuing variation in the Antarctic meridional overturning circulation (MOC) that is indicative of the Antarctic Bottom Water (AABW) formation exerts a significant influence on the abyssal circulation of the globe, particularly the Pacific. This controls the bipolar seesaw balance between deep and bottom waters at the equator. The EDT mode controlled by northward Ekman transport under the oscillating SH westerly winds generates a signal that propagates northward along the upper ocean and passes through the equator. The variation in the western boundary current (WBC) is much stronger in the North Atlantic than in the North Pacific, which appears to be associated with the relatively strong and persistent Mindanao Current (i.e., the southward flowing WBC of the North Pacific tropical gyre). The North Atlantic Deep Water (NADW) formation is controlled by salt advected northward by the North Atlantic WBC.

Satellite-Derived Tropical Cyclone Intensity in the North Pacific Ocean Using the Deviation-Angle Variance Technique

2014 ◽  
Vol 29 (3) ◽  
pp. 505-516 ◽  
Author(s):  
Elizabeth A. Ritchie ◽  
Kimberly M. Wood ◽  
Oscar G. Rodríguez-Herrera ◽  
Miguel F. Piñeros ◽  
J. Scott Tyo
Keyword(s):  
Tropical Cyclone ◽  
North Atlantic ◽  
North Pacific ◽  
Western North Pacific ◽  
North Pacific Ocean ◽  
Deviation Angle ◽  
Intensity Estimation ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

Abstract The deviation-angle variance technique (DAV-T), which was introduced in the North Atlantic basin for tropical cyclone (TC) intensity estimation, is adapted for use in the North Pacific Ocean using the “best-track center” application of the DAV. The adaptations include changes in preprocessing for different data sources [Geostationary Operational Environmental Satellite-East (GOES-E) in the Atlantic, stitched GOES-E–Geostationary Operational Environmental Satellite-West (GOES-W) in the eastern North Pacific, and the Multifunctional Transport Satellite (MTSAT) in the western North Pacific], and retraining the algorithm parameters for different basins. Over the 2007–11 period, DAV-T intensity estimation in the western North Pacific results in a root-mean-square intensity error (RMSE, as measured by the maximum sustained surface winds) of 14.3 kt (1 kt ≈ 0.51 m s−1) when compared to the Joint Typhoon Warning Center best track, utilizing all TCs to train and test the algorithm. The RMSE obtained when testing on an individual year and training with the remaining set lies between 12.9 and 15.1 kt. In the eastern North Pacific the DAV-T produces an RMSE of 13.4 kt utilizing all TCs in 2005–11 when compared with the National Hurricane Center best track. The RMSE for individual years lies between 9.4 and 16.9 kt. The complex environment in the western North Pacific led to an extension to the DAV-T that includes two different radii of computation, producing a parametric surface that relates TC axisymmetry to intensity. The overall RMSE is reduced by an average of 1.3 kt in the western North Pacific and 0.8 kt in the eastern North Pacific. These results for the North Pacific are comparable with previously reported results using the DAV for the North Atlantic basin.

scholarly journals Dynamical and biogeochemical control on the decadal variability of ocean carbon fluxes

2012 ◽  
Vol 3 (2) ◽  
pp. 1347-1389
Author(s):  
R. Séférian ◽  
L. Bopp ◽  
D. Swingedouw ◽  
J. Servonnat
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Carbon Flux ◽  
Carbon Fluxes ◽  
Modes Of Variability ◽  
The North ◽  
The North Atlantic ◽  
Ocean Carbon ◽  
The North Pacific ◽  
Regional Variance

Abstract. Several recent observation-based studies suggest that ocean anthropogenic carbon uptake has slowed down due to the impact of anthropogenic forced climate change. However, it remains unclear if detected changes over the recent time period can really be attributed to anthropogenic climate change or to natural climate variability (internal plus naturally forced variability). One large uncertainty arises from the lack of knowledge on ocean carbon flux natural variability at the decadal time scales. To gain more insights into decadal time scales, we have examined the internal variability of ocean carbon fluxes in a 1000-yr long preindustrial simulation performed with the Earth System Model IPSL-CM5A-LR. Our analysis shows that ocean carbon fluxes exhibit low-frequency oscillations that emerge from their year-to-year variability in the North Atlantic, the North Pacific, and the Southern Ocean. In our model, a 20-yr mode of variability in the North Atlantic air-sea carbon flux is driven by sea surface temperature variability and accounts for ~40% of the interannual regional variance. The North Pacific and the Southern Ocean carbon fluxes are also characterized by decadal to multi-decadal modes of variability (10 to 50 yr) that account for 30–40% of the interannual regional variance. But these modes are driven by the vertical supply of dissolved inorganic carbon through the variability of Ekman-induced upwelling and deep-mixing events. Differences in drivers of regional modes of variability stem from the coupling between ocean dynamics variability and the ocean carbon distribution, which is set by large-scale secular ocean circulation.

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