Observational Studies of General Circulation Patterns

Namias, Jerome; Clapp, Philip F.

doi:10.1007/978-1-940033-70-9_46

Cited by 33 publications

(18 citation statements)

References 34 publications

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“…Since blocking patterns are characterized by an appreciable mass difference between high and middle latitudes (Namias and Clapp 1951;Austin 1980;Treidl et al 1981) and anomalous easterly winds, the blocking index used here is an adapted version of the TM90 index (see Trigo et al 2004), which is based on the original criterion proposed by LO83. According to the LO83 criterion, a blocking event can be identified when the averaged zonal index (referred to hereafter as LO) computed as the 500-hPa height difference between 40°a nd 60°N, is negative over 30°in longitude and during five or more days (Fig.…”

Section: A Blocking Indexmentioning

confidence: 99%

A Climatology of Northern Hemisphere Blocking

et al. 2006

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In this paper a 55-yr (1948-2002) Northern Hemisphere blocking climatology is presented. Traditional blocking indices and methodologies are revised and a new blocking detection method is designed. This algorithm detects blocked flows and provides for a better characterization of blocking events with additional information on blocking parameters such as the location of the blocking center, the intensity, and extension. Additionally, a new tracking procedure has been incorporated following simultaneously the individual evolution of blocked flows and identifying coherently persistent blocked patterns.Using this method, the longest known Northern Hemisphere blocking climatology is obtained and compared with previous studies. A new regional classification into four independent blocking sectors has been obtained based on the seasonally preferred regions of blocking formation: Atlantic (ATL), European (EUR), West Pacific (WPA), and East Pacific (EPA). Global and regional blocking characteristics have been described, examining their variability from the seasonal to interdecadal scales.The global long-term blocking series in the North Hemisphere showed a significant trend toward weaker and less persistent events, as well as regional increases (decreases) in blocking frequency over the WPA (ATL and EUR) sector. The influence of teleconnection patterns (TCPs) on blocking parameters is also explored, being confined essentially to wintertime, except in the WPA sector. Additionally, regional blocking parameters, especially frequency and duration, are sensitive to regional TCPs, supporting the regional classification obtained in this paper. The ENSO-related blocking variability is evident in blocking intensities and preferred locations but not in frequency. Finally, the dynamical connection between blocking occurrence and regional TCPs is examined through the conceptual model proposed by Charney and DeVore. Observational evidence of a dynamical link between the asymmetrical temperature distributions induced by TCPs and blocking variability is provided with a distinctive contrast "warm ocean/cold land" pattern favoring the blocking occurrence in winter. However, the conceptual model is not coherent in the WPA sector, suggesting different blocking mechanisms operating in this sector.

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Section: A Blocking Indexmentioning

confidence: 99%

A Climatology of Northern Hemisphere Blocking

et al. 2006

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“…Since the advent of radiosonde networks, it has been known that the north circumpolar vortex at jet stream level exhibits seasonal fluctuations characterized by vortex expansion in winter and contraction in summer [e.g., Namias and Clapp, 1951]. Subtle changes of similar nature could be expected to accompany climatic cooling or warming, so that the size of the 300 mbar north circumpolar vortex is also a quantity to monitor for climate change.…”

Section: Introductionmentioning

confidence: 99%

Contraction of the 300 mbar north circumpolar vortex during 1963–1997 and its movement into the eastern hemisphere

Angell¹

1998

J. Geophys. Res.

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“…Examination of a typical upper-air coverage 3 shows that a reasonably dense radiosonde network is available over practically the whole area north of latitude 30°, with the exception of China and extensive parts of the Pacific Ocean. There are, _ 3 See, e.g., example given in [7]. Except for certain aircraft reconnaissance flights and a few stations missing due to communications, this example is still representative, tive.…”

Section: The Hemispheric Observation Networkmentioning

confidence: 98%

“…Namias and Clapp [7], drawing attention to the concentration of observations in certain regions, have suggested that "it would appear preferable to reduce the amount of data in populated areas and use the money thus saved to increase the number of reports, particularly upper-air reports, from remote areas." While a certain concentration is desirable in the regions most frequented by synoptic disturbances, the present underdevelopment of the net work in certain areas closely bounding the population centers is a matter of serious concern.…”

Section: The Hemispheric Observation Networkmentioning

confidence: 99%

Analysis and Data Problems in Relation to Numerical Prediction

Newton

1954

Bulletin of the American Meteorological Society

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Instantaneous height tendencies computed from different analyses of the same 500-mb chart illustrate that discrepancies in analysis or observations can have a serious effect on the accuracy of numerical forecasts. The present status of the Northern-Hemisphere aerological network is reviewed, stressing the inhomogeneity of the radiosonde network, the need for observations in fringe areas surrounding the present dense networks, and the desirability of more radio-wind stations. The suggestion is made that machine prognoses incorporating variations of fictitious observations could be used to evaluate the improvements needed and the desirability of setting up new aerological stations in particular locations.

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Observational Studies of General Circulation Patterns

Cited by 33 publications

References 34 publications

A Climatology of Northern Hemisphere Blocking

A Climatology of Northern Hemisphere Blocking

Contraction of the 300 mbar north circumpolar vortex during 1963–1997 and its movement into the eastern hemisphere

Analysis and Data Problems in Relation to Numerical Prediction

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