Severe mesoscale weather events over the Nordic Seas: Numerical modelling and sensitivity experiments

• Published in: Quarterly Journal of the Royal Meteorological Society
• Main Author: Adakudlu, Muralidhar
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Bergen 2011
• Subjects: VDP::Mathematics and natural science: 400::Geosciences: 450::Meteorology: 453; Svalbard; Svalbard Archipelago; Hinlopen Strait; IPY; Nordic Seas
• Online Access: https://hdl.handle.net/1956/4870

The Nordic seas region, due to its unique geographical and climatological conditions, experiences a number of adverse mesoscale weather events that have proven fatal for human activities in the area. Most of these weather events occur in the winter season and include orography-induced wind extremes, shallow and sharp fronts that often form in the vicinity of the ice edge and intense storms called polar lows. In order to assess such high impact weather conditions, a field campaign was conducted over the Nordic seas in February-March 2008 as part of the IPY-THORPEX project. During this field campaign, measurements of a number of severe weather cases were collected through the dropsonde and lidar sensors on-board the DLR-FALCON aircraft. This thesis deals with high resolution modeling experiments of some of the cases observed during the IPY-THORPEX field campaign, with focus on the sensitivity of these events to underlying surface conditions and several physical factors. The results of these experiments are presented in the form of three scientific articles. Paper-I presents the airborne measurements of a case with strong gap winds observed at the exit region of the Hinlopen Strait in Svalbard archipelago. The DLRFALCON aircraft flew along the Hinlopen strait and recorded winds of strength ~ 20 ms−1, which was about four times higher than the upstream wind, near to the surface. In addition, formation of a wake with return currents in the lee of the terrain was also recorded by the lidar sensors carried by the aircraft. This case was simulated in a fineresolution numerical model with a high degree of accuracy. The simulations showed the existence of small-scale cloud banners extending downstream of the lee of the mountains. The causal mechanisms for such cloud features were investigated through an idealised approach. The ideal experiments indicated that the vertical circulations set up by the terrain features cause the cloud banners and a relatively warm ocean surface maintains them by supplying moisture and ...