Multifractal Analysis for Evaluating the Representation of Clouds in Global Kilometre-Scale Models

Geophysical Research Letters American Geophysical Union (2024)

Authors:

Lilli Freischem, Philipp Weiss, HANNAH CHRISTENSEN, Philip STIER

Multifractal Analysis for Evaluating the Representation of Clouds in Global Kilometer-Scale Models

Geophysical Research Letters, 51 (2024)

Authors:

Lilli J Freischem, Philipp Weiss, Hannah M Christensen, Philip Stier

Abstract:

Clouds are one of the largest sources of uncertainty in climate predictions. Global km-scale models need to simulate clouds and precipitation accurately to predict future climates. To isolate issues in their representation of clouds, models need to be thoroughly evaluated with observations. Here, we introduce multifractal analysis as a method for evaluating km-scale simulations. We apply it to outgoing longwave radiation fields to investigate structural differences between observed and simulated anvil clouds. We compute fractal parameters which compactly characterize the scaling behavior of clouds and can be compared across simulations and observations. We use this method to evaluate the nextGEMS ICON simulations via comparison with observations from the geostationary satellite GOES-16. We find that multifractal scaling exponents in the ICON model are significantly lower than in observations. We conclude that too much variability is contained in the small scales (<100 km) leading to less organized convection and smaller, isolated anvils.

Association between feel-like temperatures and injury risk during international outdoor athletic championships: a prospective cohort study on 29 579 athlete starts during 10 championships

British Journal of Sports Medicine BMJ Publishing Group 59:1 (2024) 36-47

Authors:

Pascal Edouard, Pierre-Eddy Dandrieux, Milan Kloewer, Astrid Junge, Sébastien Racinais, Pedro Branco, Karsten Hollander, Laurent Navarro

Abstract:

Objective: To analyse associations between feel-like temperatures measured with the universal thermal climate index (UTCI) and injury rates during international athletic championships.

Methods: During 10 international outdoor athletic championships from 2007 to 2022, in-competition injuries were collected by medical teams and local organising committees. UTCI was extracted hourly from a global reanalysis of observed atmospheric conditions during each championship. We performed Poisson regressions with incidence rates (number of injuries per 1000 athlete starts) as outcomes and UTCI as a predictive variable adjusted for sex, for all and time-loss injuries, for different injured tissue types (ie, muscle, tendon, ligament, articular, bone and skin) and specific discipline (ie, sprints, hurdles, jumps, throws, middle distance, long distance, marathon and race walking).

Results: A total of 1203 in-competition injuries were reported for 29 579 athlete starts. For all in-competition injuries (ie, all injured tissue types and all disciplines), higher UTCI was associated with lower incidence rates for time-loss injuries (IRR=0.98, 95% CI 0.97 to 0.98) but not for all injuries (IRR=1.00, 95% CI 1.00 to 1.01). Based on injured tissue type with all disciplines included, higher UTCI was associated with lower incidence rates for all (IRR=0.97, 95% CI 0.97 to 0.98) and time-loss (IRR=0.96, 95% CI 0.96 to 0.96) muscle injuries. Based on the specific discipline, higher UTCI was associated with lower incidence rates for all and time-loss muscle injuries for sprints (IRR=0.95, 95% CI 0.95 to 0.96, and IRR=0.94, 95% CI 0.93 to 0.94, respectively), hurdles (IRR=0.97, 95% CI 0.96 to 97, and IRR=0.95, 95% CI 0.94 to 0.96, respectively) and throws (IRR=0.97, 95% CI 0.97 to 0.98).

Conclusions: Higher feel-like temperatures were associated with a decreased risk of time-loss and muscle injuries, particularly in sprints, hurdles and throws. Although the precise mechanism for lower injury rates with higher feel-like temperatures requires further investigation, adapting preparations such as warm-up or clothing to forecasted weather conditions may be of benefit.

Combined Impacts of Temperature, Sea Ice Coverage, and Mixing Ratios of Sea Spray and Dust on Cloud Phase Over the Arctic and Southern Oceans

Geophysical Research Letters Wiley 51:20 (2024) e2024GL110325

Authors:

Barbara Dietel, Hendrik Andersen, Jan Cermak, Philip Stier, Corinna Hoose

Abstract:

We analyze the importance of cloud top temperature, dust aerosol, sea salt aerosol, and sea ice cover for the thermodynamic phase of low‐level, mid‐level, and mid to low‐level clouds observed by CloudSat/CALIPSO over the Arctic and the Southern Ocean using an explainable machine learning technique. As expected, the cloud top temperature is found to be the most important parameter for determining cloud phase. The results show also a predictive power of sea salt and sea ice on the phase of low‐level clouds, while in mid‐level clouds dust shows predictive power. Over the Southern Ocean, strong zonal winds coincide with the aerosol distribution. While they can produce high mixing ratios of sea spray at lower levels, the strong zonal winds may prevent the pole‐ward transport of dust. Sea ice may prevent the release of sea salt aerosols and marine organic aerosols leading to higher liquid fractions in clouds over sea ice.

Multifractal Analysis for Evaluating the Representation of Clouds in Global Kilometre-Scale Models

(2024)

Authors:

Lilli Johanna Freischem, Philipp Weiss, Hannah Christensen, Philip Stier