A Diagnostic Study of the Potential Vorticity in a Warm Blocking Anticyclone

On 16-17 November, 2015, north and middle regions of Saudi Arabia were hit by a case of cyclogenesisassociated with heavy rainfall. This work presents a diagnostic study of this heavy rainfallcase based on the analysis of diabatic heating and potential vorticity. The synoptic analysis investigate that the important dynamical factors that causes this case are the northward extension of Red Sea Trough, anticyclone over the Arabian Peninsula, a travailing midlatitude upper trough, moisture transport pathways and strong upward motion arising from tropospheric instability. The calculation of diabatic heating by the thermodynamic equation illustrate that the contribution of vertical temperature advection and the adiabatic term are opposite to each other during the period of study. The largest contribution of the horizontal cold advection occurs during the first two days while the largest contribution of the horizontal warm advection occurs during the maximum development days. The dynamics of the studied case are also investigated in terms of isobaric Potential Vorticity. It is found that the location of the low-level Potential Vorticity anomaly and the Potential Vorticity generation estimates coincides with the heating region, which implies that condensation supports a large enough source to explain the existence of the low-level Potential Vorticity anomaly.

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Vortex–Vortex Interactions for the Maintenance of Blocking. Part I: The Selective Absorption Mechanism and a Case Study

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-11-0295.1 ◽

2013 ◽

Vol 70 (3) ◽

pp. 725-742 ◽

Cited By ~ 26

Author(s):

Akira Yamazaki ◽

Hisanori Itoh

Keyword(s):

Potential Vorticity ◽

Trajectory Analysis ◽

Selective Absorption ◽

Absorption Mechanism ◽

Vortex Interactions ◽

Maintenance Mechanism ◽

Blocking Anticyclone ◽

Synoptic Eddies

Abstract A new block maintenance mechanism, the selective absorption mechanism (SAM), is proposed. According to this mechanism, which is based on vortex–vortex interactions (i.e., the interactions between a blocking anticyclone and synoptic eddies with the same polarity), a blocking anticyclone actively and selectively absorbs synoptic anticyclones (strictly, air parcels with low potential vorticity). The blocking anticyclone, which is thus supplied with low potential vorticity of the synoptic anticyclones, can subsist for a prolonged period, withstanding dissipation. The SAM was verified in a case study through trajectory analysis. Ten actual cases of blocking were examined. Trajectories were calculated by tracing parcels originating from synoptic anticyclones and cyclones located upstream of the blocking. Parcels starting from anticyclones were attracted to and absorbed by the blocking anticyclone, whereas parcels from cyclones were repelled by the blocking anticyclone and attracted to the blocking cyclone, if one was present. The results show that the SAM is effective in the maintenance of observed cases of blocking. In addition, the uniqueness and distinction of the SAM from other previously proposed maintenance mechanisms are discussed.

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