scholarly journals Is Blocking a Circulation Regime?

2007 ◽  
Vol 135 (6) ◽  
pp. 2406-2413 ◽  
Author(s):  
Cristiana Stan ◽  
David M. Straus
Keyword(s):  
Large Scale ◽  
Temperature Anomaly ◽  
Potential Temperature ◽  
Weather Extremes ◽  
Large Scale Circulation ◽  
The Pacific ◽  
Tightly Coupled ◽  
Constant Potential ◽  
The Relationship ◽  
Blocking Index

Abstract The relationship between Pacific blocking and large-scale circulation regimes is investigated. The large-scale circulation regimes are obtained by cluster analysis using the k-means method and tested against significance and reproducibility. Pacific blocking is described using two different methods. In a direct approach, blocking is described by a recently developed blocking index, which is defined in terms of potential temperature anomaly on a surface of constant potential vorticity. In an indirect approach, the occurrence of extreme events is used as a proxy for blockings. Between the two methods there is a causal relationship; the direct one is an indication of the occurrence of the blocking, while the indirect one is a measure of some of the effects caused by the blocking. The results indicate that large-scale circulation regimes are related to but not necessarily tightly coupled to blocking and weather extremes in the Pacific–North America region.

scholarly journals Transition from Suppressed to Active Convection Modulated by a Weak Temperature Gradient–Derived Large-Scale Circulation

2015 ◽  
Vol 72 (2) ◽  
pp. 834-853 ◽  
Author(s):  
C. L. Daleu ◽  
S. J. Woolnough ◽  
R. S. Plant
Keyword(s):  
Temperature Gradient ◽  
Large Scale ◽  
Deep Convection ◽  
Potential Temperature ◽  
Mean Value ◽  
Transition Time ◽  
Large Scale Circulation ◽  
Transition Times ◽  
Active Convection ◽  
Fully Coupled

Abstract Numerical simulations are performed to assess the influence of the large-scale circulation on the transition from suppressed to active convection. As a model tool, the authors used a coupled-column model. It consists of two cloud-resolving models that are fully coupled via a large-scale circulation that is derived from the requirement that the instantaneous domain-mean potential temperature profiles of the two columns remain close to each other. This is known as the weak temperature gradient approach. The simulations of the transition are initialized from coupled-column simulations over nonuniform surface forcing, and the transition is forced in the dry column by changing the local and/or remote surface forcings to uniform surface forcing across the columns. As the strength of the circulation is reduced to zero, moisture is recharged into the dry column and a transition to active convection occurs once the column is sufficiently moistened to sustain deep convection. Direct effects of changing surface forcing occur over the first few days only. Afterward, it is the evolution of the large-scale circulation that systematically modulates the transition. Its contributions are approximately equally divided between the heating and moistening effects. A transition time is defined to summarize the evolution from suppressed to active convection. It is the time when the rain rate in the dry column is halfway to the mean value obtained at equilibrium over uniform surface forcing. The transition time is around twice as long for a transition that is forced remotely compared to a transition that is forced locally. Simulations in which both local and remote surface forcings are changed produce intermediate transition times.

scholarly journals Can seafloor voltage cables be used to study large-scale circulation? An investigation in the Pacific Ocean

Ocean Science ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 383-392
Author(s):  
Jakub Velímský ◽  
Neesha R. Schnepf ◽  
Manoj C. Nair ◽  
Natalie P. Thomas
Keyword(s):  
Pacific Ocean ◽  
Flow Velocity ◽  
Ocean Circulation ◽  
Large Scale ◽  
Eastern Pacific ◽  
Low Flow ◽  
Large Scale Circulation ◽  
Numerical Predictions ◽  
The Pacific ◽  
The Pacific Ocean

Abstract. Marine electromagnetic (EM) signals largely depend on three factors: flow velocity, Earth's main magnetic field, and seawater's electrical conductivity (which depends on the local temperature and salinity). Because of this, there has been recent interest in using marine EM signals to monitor and study ocean circulation. Our study utilizes voltage data from retired seafloor telecommunication cables in the Pacific Ocean to examine whether such cables could be used to monitor circulation velocity or transport on large oceanic scales. We process the cable data to isolate the seasonal and monthly variations and then evaluate the correlation between the processed data and numerical predictions of the electric field induced by an estimate of ocean circulation. We find that the correlation between cable voltage data and numerical predictions strongly depends on both the strength and coherence of the model velocities flowing across the cable, the local EM environment, as well as the length of the cable. The cable within the Kuroshio Current had good correlation between data and predictions, whereas two of the cables in the Eastern Pacific Gyre – a region with both low flow speeds and interfering velocity directions across the cable – did not have any clear correlation between data and predictions. Meanwhile, a third cable also located in the Eastern Pacific Gyre showed good correlation between data and predictions – although the cable is very long and the speeds were low, it was located in a region of coherent flow velocity across the cable. While much improvement is needed before utilizing seafloor voltage cables to study and monitor oceanic circulation across wide regions, we believe that with additional work, the answer to the question of whether or not seafloor voltage cables can be used to study large-scale circulation may eventually be yes.

scholarly journals Recent climate variation in the Bering and Chukchi Seas and its linkages to large-scale circulation in the Pacific

2014 ◽  
Vol 42 (9-10) ◽  
pp. 2423-2437 ◽  
Author(s):  
Sae-Rim Yeo ◽  
Kwang-Yul Kim ◽  
Sang-Wook Yeh ◽  
Baek-Min Kim ◽  
Taehyoun Shim ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Variation ◽  
Large Scale Circulation ◽  
The Pacific ◽  
Recent Climate

scholarly journals Variability of the Great Plains Low-Level Jet: Large-Scale Circulation Context and Hydroclimate Impacts

2008 ◽  
Vol 21 (7) ◽  
pp. 1532-1551 ◽  
Author(s):  
Scott J. Weaver ◽  
Sumant Nigam
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Core Region ◽  
Large Scale Circulation ◽  
Diurnal Variability ◽  
Low Level ◽  
The Pacific ◽  
Gulf States ◽  
Low Level Jet ◽  
Peak Phase

Abstract Variability of the Great Plains low-level jet (GPLLJ) is analyzed from the perspective of larger-scale, lower-frequency influences and regional hydroclimate impacts as opposed to the usual analysis of its frequency, diurnal variability, and mesoscale structure. The circulation-centric core analysis is conducted with monthly data from the high spatiotemporal resolution, precipitation-assimilating North American Regional Reanalysis, and the 40-yr ECMWF Re-Analysis (ERA-40) (as necessary) to identify the recurrent patterns of GPLLJ variability and their large-scale circulation links. The links are first investigated from regressions of an index representing meridional wind speed in the climatological jet-core region; the core region itself is defined from analysis of seasonal and diurnal variability of the jet structure and moisture fluxes. The analysis reveals that GPLLJ variability is, indeed, linked to coherent, large-scale, upper-level height patterns over the Pacific and North Atlantic Oscillation (NAO) variability in the Atlantic. A Rossby wave source analysis shows the Pacific height pattern to be potentially linked to tropical diabatic heating anomalies in the west-central basin and in the eastern Pacific sector. EOF analysis of GPLLJ variability shows it to be composed of three modes that, together, account for ∼75% of the variance. The modes represent the strengthening/expansion of the jet core (38%), with a strong precipitation impact on the northern Great Plains, and linked to post-peak-phase ENSO variability; meridional shift of the GPLLJ (23%), with a Gulf states precipitation focus, and linked to pre-peak-phase ENSO variability; and in-place strengthening of the GPLLJ (12%), with dipolar influence on Great Plains and Gulf states precipitation, and linked to summer NAO variability.

NORTHEAST PACIFIC SEAWATER RADIOCARBON RECORDED IN ABALONE SHELLS OBTAINED FROM OTSUCHI BAY, JAPAN

Radiocarbon ◽  
2019 ◽  
pp. 1-10 ◽  
Author(s):  
Kosuke Ota ◽  
Yusuke Yokoyama ◽  
Yosuke Miyairi ◽  
Jun Hayakawa ◽  
Naomi Satoh ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Large Scale ◽  
Dissolved Inorganic Carbon ◽  
Coastal Ecosystems ◽  
Coastal Regions ◽  
Otsuchi Bay ◽  
The Pacific ◽  
Abalone Shell ◽  
The Relationship ◽  
Northern Japan

ABSTRACTReconstructing past ocean currents in the coastal regions is necessary to better understand the relationship between oceanographic changes and coastal ecosystems. It is known that variations have occurred with large-scale climate changes such as ENSO (El Niño Southern Oscillations) and PDO (Pacific Decadal Oscillations). Thus, reconstruction of past seawater conditions in coastal regions is needed to better understand the relationship between oceanographic changes and coastal ecosystems. Seawater radiocarbon is a unique proxy to understand the properties of water masses. Reef-building corals have been employed extensively and successfully in conducting this type of research into past ocean circulation histories. However, their distribution is limited to the low latitudes and hence alternative archives are required for studies in mid to high-latitude locations. Here, we use abalone shell samples obtained from Otsuchi Bay located in the Tohoku region on the Pacific coast of Northern Japan. Radiocarbon in abalone shells was compared with dissolved inorganic carbon in two-year-long records of river water as well as seawater. The data indicate that abalone shells can be used to reconstruct past seawater radiocarbon variations in northern Japan where coral skeletons are not available for ocean mixing studies.

scholarly journals Greenland accumulation and its connection to the large-scale atmospheric circulation in ERA-Interim and paleoclimate simulations

2013 ◽  
Vol 9 (6) ◽  
pp. 2433-2450 ◽  
Author(s):  
N. Merz ◽  
C. C. Raible ◽  
H. Fischer ◽  
V. Varma ◽  
M. Prange ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Climate Model ◽  
Ice Core ◽  
Ice Cores ◽  
Circulation Pattern ◽  
Large Scale Circulation ◽  
Atmospheric Circulation Patterns ◽  
The Stability ◽  
The Relationship

Abstract. Changes in Greenland accumulation and the stability in the relationship between accumulation variability and large-scale circulation are assessed by performing time-slice simulations for the present day, the preindustrial era, the early Holocene, and the Last Glacial Maximum (LGM) with a comprehensive climate model. The stability issue is an important prerequisite for reconstructions of Northern Hemisphere atmospheric circulation variability based on accumulation or precipitation proxy records from Greenland ice cores. The analysis reveals that the relationship between accumulation variability and large-scale circulation undergoes a significant seasonal cycle. As the contributions of the individual seasons to the annual signal change, annual mean accumulation variability is not necessarily related to the same atmospheric circulation patterns during the different climate states. Interestingly, within a season, local Greenland accumulation variability is indeed linked to a consistent circulation pattern, which is observed for all studied climate periods, even for the LGM. Hence, it would be possible to deduce a reliable reconstruction of seasonal atmospheric variability (e.g., for North Atlantic winters) if an accumulation or precipitation proxy were available that resolves single seasons. We further show that the simulated impacts of orbital forcing and changes in the ice sheet topography on Greenland accumulation exhibit strong spatial differences, emphasizing that accumulation records from different ice core sites regarding both interannual and long-term (centennial to millennial) variability cannot be expected to look alike since they include a distinct local signature. The only uniform signal to external forcing is the strong decrease in Greenland accumulation during glacial (LGM) conditions and an increase associated with the recent rise in greenhouse gas concentrations.

scholarly journals Ability of RCM/GCM couples to represent the relationship of large scale circulation to climate extremes over the Mediterranean region

2011 ◽  
Vol 46 (3) ◽  
pp. 197-209 ◽  
Author(s):  
HA Flocas ◽  
M Hatzaki ◽  
K Tolika ◽  
C Anagnostopoulou ◽  
E Kostopoulou ◽  
...  
Keyword(s):  
Mediterranean Region ◽  
Large Scale ◽  
Climate Extremes ◽  
Large Scale Circulation ◽  
The Mediterranean ◽  
Relationship Of ◽  
The Relationship
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