Abstract:
The AROME-Arctic model is widely used for forecasting weather conditions in the Norwegian Sea. However, forecasting cloud properties and evolution remains challenging, as cloud dynamics fall within a model "grey zone" due to finite resolution and parameterization challenges. During the Cold Air outbreak Experiment in the Sub-Arctic Region (CAESAR), a classic marine cold air outbreak (MCAO) was sampled by aircraft on 16 March 2024. This research flight has provided new measurements of MCAO cloud development in this "grey zone" region, opening the door for a model/observation evaluation. During this research flight, 36 dropsondes were deployed along a transect spanning a developed polar low, MCAO cloud streets, and the sea-ice region from which the MCAO originated. SHF and LHF were derived from dropsonde measurements and collocated with interpolated AROME-Arctic forecasts from T-60 to T-6 hours prior to the flight. Overall, AROME-Arctic was remarkably consistent in producing the MCAO event. Dropsonde-estimated SHF values were 200–300 W m⁻² in the polar low region, increasing to nearly 400 W m⁻² near the sea-ice edge. LHF values ranged from 150–300 W m⁻² in the polar low region, decreasing toward the sea-ice edge. AROME-Arctic overestimated SHF by 30–40% through the MCAO cloud street region, with maximum SHF biases near the sea-ice edge. Persistent LHF biases were also present across the flight transect, with improved performance in the cloud street region closer to the sea ice edge. Cloud-top altitude forecasts were excellent through much of the cloud street region but too low near the sea-ice edge and within the polar low, suggesting potential issues in how AROME-Arctic couples the surface and atmosphere. In addition to the 16 March 2024 flight, two additional case studies are evaluated: (1) a second classic but weaker MCAO event from 11 March 2024, and (2) a "MCAO-like" event on 28 February 2024. Similar high SHF biases in AROME-Arctic are noted again for the 11 March 2026 case, but not the 28 March 2026 case. Differences in air mass origin and properties (including relative humidity and temperatures differences) relative to the dropsondes are hypothesized to explain why AROME-Arctic SHF values near the sea ice edge are too large with preliminary analysis discussed.
What is the Joint Oslo Seminar (JOS):
- Atmospheric and climate sciences have a stronghold in Oslo among the four institutions University of Oslo, the Meteorological Institute, CICERO and NILU.
- This joint seminar invites renowned international experts to contribute to an informal series of lectures, meant to create interaction with the Oslo atmospheric and climate science community on recent highlights and analysis in the field.
- Normally seminars will be held on Thursdays (12:15 pm -1pm).