Weather and Climate Dynamics
Weather and Climate Dynamics
Weather and Climate Dynamics
Preprints
https://doi.org/10.5194/wcd-2020-57
https://doi.org/10.5194/wcd-2020-57

  15 Dec 2020

15 Dec 2020

Review status: this preprint is currently under review for the journal WCD.

Atmospheric convergence zones stemming from large-scale mixing

Gabriel M. P. Perez1, Pier Luigi Vidale1,2, Nicholas P. Klingaman1,2, and Thomas C. M. Martin3 Gabriel M. P. Perez et al.
  • 1Department of Meteorology, University of Reading, Reading, United Kingdom
  • 2National Centre for Atmospheric Science, Reading, United Kingdom
  • 3Department of Atmospheric Sciences, University of São Paulo, São Paulo, Brazil

Abstract. Organised cloud bands are important features of tropical and subtropical rainfall. These structures are often regarded as convergence zones, alluding to an association with coherent atmospheric flow. However, the flow kinematics is not usually taken into account in classification methods for this type of event, as large-scale lines are rarely evident in instantaneous diagnostics such as Eulerian convergence. Instead, existing convergence zone definitions rely on heuristic rules of shape, duration and size of cloudiness fields. Here we investigate the role of large-scale turbulence in shaping atmospheric moisture in South America. We employ the Finite-Time Lyapunov Exponent (FTLE), a metric of deformation among neighboring trajectories, to define convergence zones as attracting Lagrangian Coherent Structures (LCSs). Attracting LCSs frequent tropical and subtropical South America, with climatologies consistent with the South Atlantic Convergence Zone (SACZ), the South American Low-level Jet (SALLJ) and the Intertropical Convergence Zone (ITCZ). In regions under the direct influence of the ITCZ and the SACZ, rainfall is significantly positively correlated with large-scale mixing measured by the FTLE. Attracting LCSs in South and Southeast Brazil are associated with significant positive rainfall and moisture flux anomalies. Geopotential height composites suggest that the occurrence of attracting LCSs in these regions is related with teleconnection mechanisms such as the Pacific-South Atlantic. We believe that this kinematical approach can be used as an alternative to region-specific convergence zone classification algorithms; it may help advance the understanding of underlying mechanisms of tropical and subtropical rain bands and their role in the hydrological cycle.

Gabriel M. P. Perez et al.

 
Status: open (until 12 Feb 2021)
Status: open (until 12 Feb 2021)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
[Subscribe to comment alert] Printer-friendly Version - Printer-friendly version Supplement - Supplement

Gabriel M. P. Perez et al.

Gabriel M. P. Perez et al.

Viewed

Total article views: 210 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
160 46 4 210 2 1
  • HTML: 160
  • PDF: 46
  • XML: 4
  • Total: 210
  • BibTeX: 2
  • EndNote: 1
Views and downloads (calculated since 15 Dec 2020)
Cumulative views and downloads (calculated since 15 Dec 2020)

Viewed (geographical distribution)

Total article views: 192 (including HTML, PDF, and XML) Thereof 190 with geography defined and 2 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 15 Jan 2021
Download
Short summary
Much of the rainfall in tropical regions comes from organised cloud bands called convergence zones (CZs). These bands have hundreds of kilometers. In South America (SA), they cause intense rain for long periods of time. To study these systems, we need to define and identify them with computer code. We propose a definition of CZs based on the the pathways of air, selecting regions where air masses originated in separated regions meet. This method identifies important systems of rain in SA.