A Study of the Effects of Large Blocking Highs on the General Circulation in the Northern-Hemisphere Westerlies

Elliott, Robert D.; Smith, Theodore B.

doi:10.1175/1520-0469(1949)006<0068:asoteo>2.0.co;2

Cited by 64 publications

(45 citation statements)

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“…The higher blocking occurrence in the Pacific, the Atlantic, and over Europe was also reported by some of the very first studies of blocking climatology, such as Elliott and Smith (1949) and Rex (1950b). Attention was not given to the existence of the third area of abundant blocking over central Asia, perhaps because of the sparsity of data in the region.…”

Section: May 2008supporting

confidence: 67%

“…Berggen et al (1949) conducted a more in-depth study of the horizontal and vertical structures of the thermal and wind fields during the European blocking event of February 1948. Elliott and Smith (1949) gave a subjective catalog of blocking cases based upon the requirement that a persistent high must be identified in the latitude band 55°-60°N. The seminal study by Rex (1950a) proposed a set of criteria for the identification of blocking.…”

Section: Introductionmentioning

confidence: 99%

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Aspects of a Northern Hemisphere Atmospheric Blocking Climatology

Tyrlis

Hoskins

2008

Journal of the Atmospheric Sciences

162

135

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A comprehensive climatology of Northern Hemisphere blocking is described based on a PV-wavebreaking index at the latitude of the climatological storm track and using the 40-yr ECMWF Re-Analysis (ERA-40) dataset. The general characterization of blocking regions is in agreement with most other studies, though more detail is provided here. In the annual average, blocking is most prevalent in the large region from the eastern Atlantic Ocean through Europe to central Asia with a secondary region in the central and eastern Pacific Ocean. Using a blocking criterion with the requirement for both longitudinal extent and temporal persistence, the peak in the frequency is in the Scandinavian region, where 24% of the days are characterized by blocking. In the east Pacific maximum, the corresponding number is 7%. However, there is considerable and very important interannual variability. The decay rate in the number of blocking events lasting at least a specified number of days is significantly less over Europe than elsewhere. However, the average intensity of blocking episodes is slightly higher in the east Pacific. The mean annual cycle of blocking is quite complex. Over most of Europe it continues through the year, with maximum intensities in the autumn and winter. To both the east and west, over the western Atlantic and Asia, there are two periods in the year of highest blocking frequency. Similar two-cycle behavior is found in the eastern Pacific region. The relationship of blocking with the storm track and the mean planetary-scale geopotential ridges is considered, and the evidence that blocking is a particular phenomenon with its own nonlinear dynamics is discussed.

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Section: May 2008supporting

confidence: 67%

Section: Introductionmentioning

confidence: 99%

Aspects of a Northern Hemisphere Atmospheric Blocking Climatology

Tyrlis

Hoskins

2008

Journal of the Atmospheric Sciences

162

135

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“…Once a block is created within a jetstream, the mobile synoptic waves superimposed on the westerly are blocked by the abnormally persistent high-pressure system. This is why the system is called blocking (see Elliott and Smith, 1949;Rex, 1950). Some blocking highs are robust enough to persist about a month at the same location (see Miyakoda et al, 1983;Tan and Curry, 1993).…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of a Life-Cycle of Atmospheric Blocking and the Analysis of Potential Vorticity Using a Simple Barotropic Model

Tanaka

1998

Journal of the Meteorological Society of Japan

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In this study, we conducted a series of numerical experiments to investigate atmospheric blocking, using a simple barotropic model that featured a wavemaker to excite synoptic disturbances. The model has a resolution equivalent to R20 and consists of only five physical processes: a wavemaker as baroclinic instability, topographic forcing, biharmonic diffusion, zonal surface stress, and Ekman pumping.Results of time integrations show that persistent dipole blockings appear one after another in the model, showing a reasonable life-cycle. In the model atmosphere, the synoptic disturbances are amplified exponentially by the wavemaker. The exponential growth soon saturates with nonlinear scattering of energy from synoptic to planetary waves associated with a Rossby wave breaking. The analysis of potential vorticity (PV) indicates that the onset of blocking is brought on by the Rossby wave breaking. The overturning of high and low PVs tends to occur at the topographic stationary ridge.Once a block is formed by the Rossby wave breaking, subsequent Rossby waves are blocked and undergo meridional stretch. The stretched wave then breaks down, depositing fresh low PV at the north and high PV at the south of the blocking system to maintain the block. The result is consistent with the so-called eddy straining mechanism. The result suggests that the exponential growth of synoptic disturbances is essential both for the onset and the maintenance of blocking.

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“…Atmospheric blocking, both the phenomenon itself and its representation in numerical climate models, has been studied for almost seventy years (Elliott and Smith, 1949;Rex, 1950), especially in the Northern Hemisphere. Events occur most frequently at, and downstream of, the jet maxima (Rex, 1950;CrociMaspoli et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Resolution, physics and atmosphere–ocean interaction – How do they influence climate model representation of Euro-Atlantic atmospheric blocking?

Hartung

Svensson

Kjellström

2017

Tellus A: Dynamic Meteorology and Oceanography

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Atmospheric blocking events are known to locally explain a large part of climate variability. However, despite their relevance, many current climate models still struggle to represent the observed blocking statistics. In this study, simulations of the global climate model EC-Earth are analysed with respect to atmospheric blocking. Seventeen simulations map the uncertainty space defined by the three-model characteristics: atmospheric resolution, physical parameterization and complexity of atmosphere-ocean interaction, namely an atmosphere coupled to an ocean model or forced by surface data. Representation of the real-world statistics is obtained from reanalyses ERA-20C, JRA-55 and ERA-Interim which agree on Northern Hemisphere blocking characteristics. Blocking events are detected on a central blocking latitude which is individually determined for each simulation. The frequency of blocking events tends to be underestimated relative to ERA-Interim over the Atlantic and western Eurasia in winter and overestimated during spring months. However, only few model setups show statistically significant differences compared to ERA-Interim which can be explained by the large inter-annual variability of blocking. Results indicate slightly larger biases relative to ERA-Interim in coupled than in atmosphere-only models but differences between the two are not statistically significant. Although some resolution dependence is present in spring, the signal is weak and only statistically significant if the physical parameterizations of the model are improved simultaneously. Winter blocking is relatively more sensitive to physical parameterizations, and this signal is robust in both atmosphere-only and coupled simulations, although stronger in the latter. Overall, the model can capture blocking frequency well despite biases in representing the mean state of geopotential height over this area. Blocking signatures of geopotential height are represented more similar to ERA-Interim and only weak sensitivities to model characteristics remain.

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A Study of the Effects of Large Blocking Highs on the General Circulation in the Northern-Hemisphere Westerlies

Cited by 64 publications

References 0 publications

Aspects of a Northern Hemisphere Atmospheric Blocking Climatology

Aspects of a Northern Hemisphere Atmospheric Blocking Climatology

Numerical Simulation of a Life-Cycle of Atmospheric Blocking and the Analysis of Potential Vorticity Using a Simple Barotropic Model

Resolution, physics and atmosphere–ocean interaction – How do they influence climate model representation of Euro-Atlantic atmospheric blocking?

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