Cross-valley vortices in the Inn valley, Austria: Structure, evolution and governing force imbalances

Details

• Journal Title:
  Quarterly Journal of the Royal Meteorological Society
• Personal Author:
  Babić, Nevio ; Adler, Bianca ; Gohm, Alexander ; Kalthoff, Norbert ; Haid, Maren ; Lehner, Manuela ; Ladstätter, Paul ; Rotach, Mathias W.
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; PSL (Physical Sciences Laboratory) ; CIRES (Cooperative Institute for Research in Environmental Sciences)
• Description:
  Exchange of momentum and scalars in the mountain boundary layer is achieved through an interaction of meso-to-microscale motions, occurring to varying extents depending on the combined effect of thermally driven as well as dynamically driven forcings. One such motion, known as a secondary circulation, results from a horizontal force imbalance across a curved valley segment, wherein the centrifugal force towards the outside of the valley bend can create a pressure gradient force in the opposite direction. The lack of adequate measurement strategies capable of sampling such motions in curved mountain valleys explains the near-absence of any observational evidence of secondary circulations there. The goal of the CROSSINN (Cross-valley flow in the Inn valley investigated by dual-Doppler lidar measurements) campaign, conducted in a curved segment of the Inn valley, Austria, was to determine the character of the cross-valley flow by means of a coplanar retrieval applied to a multi-Doppler wind lidar configuration. A signature of a secondary circulation, hereafter referred to as a cross-valley vortex, stood out particularly during intense daytime upvalley flow episodes. Vortices were detected on 23 upvalley wind days, with a declining frequency of occurrence from August to October. Nearly all identified vortices were marked by a low-level upvalley jet, a clockwise wind direction turning with height, and a cessation of upvalley flow at the local ridgeline level. The routinely sampled coplanar-retrieved cross-valley wind field enabled the quantification of more advanced parameters based on vorticity, revealing a faster spin rate of the vortex around its streamwise axis given a stronger upvalley flow, and a period of revolution on the order of several tens of minutes. A detailed inspection of the lateral momentum budget and associated uncertainties confirmed the importance of the relationship between the centrifugal and the pressure gradient force for the cross-valley vortex occurrence in a curved valley.
• Keywords:
  Boundary Layer Circulation Lidar Mountains Vorticity Boundary Layer
• Source:
  Q J R Meteorol Soc, 147( 740, 3835– 3861
• DOI:
  https://doi.org/10.1002/qj.4159
• Document Type:
  Journal Article
• Rights Information:
  CC BY-NC-ND
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha256:2721ff89d6102db10ec99cfbcad49c5d8cc6ce73415c7c68a74f646d916d526d
• Download URL:
  https://repository.library.noaa.gov/view/noaa/44547/noaa_44547_DS1.pdf
• File Type:
  [PDF - 5.10 MB ]