The interactions between mid-latitude blocking anticyclones and synoptic-scale cyclones in the northern hemisphere

Anthony Rocco Lupo, Purdue University

Abstract

Using the Goddard Laboratory for Atmospheres GEOS-1 five year data set, horizontal and vertical distributions of atmospheric forcing processes involved in the life cycles of four Northern Hemisphere mid-latitude blocking anticyclones were examined. The complete form of the Zwack-Okossi equation was used as the primary diagnostic tool. A three-year blocking climatology reveals that the association between block development and an upstream precursor cyclone and intervening jet maximum could adequately describe every case. An analysis of the four cases, chosen from the three-year climatology so as to encompass a wide of range blocking characteristics, shows that upstream cyclones and associated jet maxima were important in block intensification and maintenance as well. The diagnostic results show that anticyclonic vorticity advection (AVA), maximizing near the 300 to 200-hPa layer, was the most consistent contributor to the 500-hPa height rises associated with block formation, and that temperature advection and adiabatic warming may contribute to these 500-hPa height rises. During decay, ageostrophic vorticity tendencies and boundary layer friction were the most consistent contributors to height falls. Additionally, in the development of blocking anticyclones characterized as mode 1 (mode 2), AVA (AVA supported by temperature advection) was the most important mechanism contributing to height rises at the block center. In partitioning the basic data fields into their planetary-scale (P) and synoptic-scale components (S), non-interaction 500-hPa height tendencies forced by processes at each scale; as well as by scale interaction 500-hPa height tendencies (I), were calculated. These results show that in mode 1 (mode 2) flow regimes the S and I (the S and P) processes were most prominent in the blocked region. In block formation, the I component, dominated by the advection of synoptic-scale anticyclonic vorticity by the planetary-scale winds, was the largest and most consistent contributor to height rises in the block center for Cases 1 and 4. For Cases 2 and 3, the S and P height rises were the largest contributors to total height rises. It was also found that the height rise regions found on the anticyclonic side of the jet maxima associated with block development and intensification were primarily comprised of the S and I component. Finally, the precursor cyclones were associated with I (S or S and I) height rises that contributed prominently to block formation in mode 1 (mode 2) flow regimes.

Degree

Ph.D.

Advisors

Smith, Purdue University.

Subject Area

Atmosphere

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