På jakt etter farbar led og bedre isvarsler

Next week’s BCCR Monday seminar will be given by Nicholas Grosfeld, who is visiting BCCR from the University of New South Wales, ARC Center of Excellence for 21st Century Weather in Australia. He will present his work on "3-dimensional insights on the climatology of midlatitude cyclones in the Southern Hemisphere.”. The seminar will take place in the usual BCCR seminar room (4th floor of the West wing) at 11:00. Abstract Synoptic cyclones are known to make important contributions to rainfall across the Southern Hemisphere landmasses. In Southern Australia, these lows underpin a key component of interannual rainfall variability, and can occasionally lead to flooding. Countless studies have employed automated identification and tracking schemes to reveal insights to these weather systems based on analysis at a single level of the troposphere, while more recent works have begun to extend the tracking process across several levels. In this talk I will first describe a simple algorithm to identify and track synoptic cyclones throughout the depth of the troposphere, which will be applied to geopotential height data in the ERA5 reanalysis, across the whole Southern Hemisphere, for the years 1979-2022. These cyclones will then be classified according to whether the system first develops in the lower, middle, or upper troposphere, and differences in the climatology of these classes of cyclones will be presented. Finally, the contribution of each of these classes of cyclones to annual rainfall across Southern Australia will be explored. Speaker information After completing high-school in rural Australia during the Millennium Drought, Nicholas completed a bachelor of science, majoring in Atmosphere and Ocean science, at the University of Melbourne, and then an honours year at UNSW. Nick’s research interest lies at the intersection of synoptic meteorology and climate dynamics, and improving the prediction of rainfall. Nick is continuing his research on the nature and variability of rain-bearing cyclones across the Southern Hemisphere mid-latitudes in a PhD at UNSW.

Dear all, This week, there will be an additional BCCR Special seminar that will be given by David WJ Thompson, who is visiting BCCR from the Department of Atmospheric Science at Colorado State University in the USA. He will present his work on "An Observational Estimate of the Pattern Effect on Climate Sensitivity”. The seminar will take place in the usual BCCR seminar room (4th floor of the West wing) at 11:00. Abstract: The "pattern effect" refers to the dependence of climate sensitivity on the spatial structure of temperature change. Most evidence for the pattern effect comes from numerical experiments. Here, I will explore the evidence for the pattern effect in observations. The observational analyses focus on the relationships between the global-mean radiative response and spatially-varying variability in the surface temperature field. It is argued that the results of the observational analyses provide a statistical analogue to the causal response functions derived from atmospheric models forced with surface temperature patches. Consistent with the feedbacks inferred from numerical experiments, the observational analyses indicate large negative internal feedbacks due to temperature variability over the western Pacific. Unlike the results inferred from such experiments, the analyses indicate equally large positive internal feedbacks over the southeastern tropical Pacific and negative internal feedbacks over land areas. When estimated from observations, temperature variability over the land areas accounts for roughly 80% of the global-mean, negative internal feedback; and temperature variability over the southeastern tropical Pacific acts to attenuate the global-mean negative internal feedback by nearly 10%.

Hi everyone, We’ll meet in the Bjerknes Meeting Room on the 3rd floor on Monday 11 August, 11–12h. A program will be sent around closer to the day, but one topic will be a discussion on Bjerknes strategy. If you have anything to share with the Hazards Group, let me know in advance. I’ll send a reminder out in early August. Enjoy the summer! Stijn