scholarly journals Characterizing the Local and Intense Water Cycle during a Cold Air Outbreak in the Nordic Seas

2018 ◽  
Vol 146 (11) ◽  
pp. 3567-3588 ◽  
Author(s):  
Lukas Papritz ◽  
Harald Sodemann
Keyword(s):  
Water Cycle ◽  
Weather Prediction ◽  
Active Regions ◽  
Numerical Weather Prediction Model ◽  
Limited Area ◽  
Nordic Seas ◽  
Cold Air ◽  
Cold Air Outbreak ◽  
Local Water ◽  
Heat And Moisture

Abstract Air masses in marine cold air outbreaks (CAOs) at high latitudes undergo a remarkable diabatic transformation because of the uptake of heat and moisture from the ocean surface, and the formation of precipitation. In this study, the fundamental characteristics of the water cycle during an intense and persistent, yet archetypal basinwide CAO from Fram Strait into the Nordic seas are analyzed with the aid of the tracer-enabled mesoscale limited-area numerical weather prediction model COSMO. A water budget of the CAO water cycle is performed based on tagged water tracers that follow moisture picked up by the CAO at various stages of its evolution. The atmospheric dynamical factors and boundary conditions that shape this budget are thereby analyzed. The water tracer analysis reveals a highly local water cycle associated with the CAO. Rapid turnover of water vapor results in an average residence time of precipitating waters of about one day. Approximately one-third of the total moisture taken up by the CAO falls as precipitation by convective overturning in the marine CAO boundary layer. Furthermore, precipitation efficiency increases as the CAO air mass matures and is exposed to warmer waters in the Norwegian Sea. These properties of the CAO water cycle are in strong contrast to situations dominated by long-range moisture transport that occur in the dynamically active regions of extratropical cyclones. It is proposed that CAOs in the confined Nordic seas provide a natural laboratory for studying local characteristics of the water cycle and evaluating its representation in models.

scholarly journals Partitioning of snowy and rainy precipitation in a case of a north Adriatic frontal passage

2006 ◽  
Vol 7 ◽  
pp. 279-284 ◽  
Author(s):  
M. Monai ◽  
A. M. Rossa ◽  
A. C. Bonan
Keyword(s):  
Adriatic Sea ◽  
Weather Prediction ◽  
Numerical Weather Prediction Model ◽  
Limited Area ◽  
Italian Region ◽  
Cold Air ◽  
The Road ◽  
North East ◽  
The North ◽  
The Alps

Abstract. A case of snow fall in the plains of the Northern Italian region Veneto is presented from a forecasters' perspective. Contrasting forecast guidance came from the ECMWF global model and the limited area model LAMI. The former showed a marked warm-moist Sirocco flow coming from the Adriatic Sea onto the coast at all levels, the latter discerned a distinct cold air flow from the north-east along the foothills of the Alps. The integrated observing network of the Centro Meteorologico di Teolo ARPA Veneto revealed this cold-air structure and helped the forecaster in the choice of the forecast and underpin the snowfall alert to the road authorities. It is argued that this feature is a crucial element for the occurrence of snowfall over the Veneto plains, and that the high-resolution numerical weather prediction model was essential in describing this mesoscale feature. The nature of the north-easterly flow is thought to be a combination of a Bora like flow and a barrier jet induced by flow blocking by the Alps.

scholarly journals Quality Assessment of Weather Radar Wind Profiles during Bird Migration

2008 ◽  
Vol 25 (12) ◽  
pp. 2188-2198 ◽  
Author(s):  
Iwan Holleman ◽  
Hans van Gasteren ◽  
Willem Bouten
Keyword(s):  
Bird Migration ◽  
Doppler Radar ◽  
Weather Prediction ◽  
Weather Radar ◽  
Numerical Weather Prediction Model ◽  
Limited Area ◽  
Migration Direction ◽  
X Band ◽  
Performance Statistics ◽  
Wind Profiles

Abstract Wind profiles from an operational C-band Doppler radar have been combined with data from a bird tracking radar to assess the wind profile quality during bird migration. The weather radar wind profiles (WRWPs) are retrieved using the well-known volume velocity processing (VVP) technique. The X-band bird radar performed range–height scans perpendicular to the main migration direction and bird densities were deduced by counting and normalizing the observed echoes. It is found that the radial velocity standard deviation (σr) obtained from the VVP retrieval is a skillful indicator of bird migration. Using a threshold of 2 m s−1 on σr, more than 93% of the bird-contaminated wind vectors are rejected while over 70% of the true wind vectors are accepted correctly. For high bird migration densities the raw weather radar wind vectors have a positive speed bias of 8.6 ± 3.8 m s−1, while the quality-controlled wind vectors have a negligible speed bias. From the performance statistics against a limited area numerical weather prediction model, it is concluded that all (significant) bird contamination is removed and that high-quality weather radar wind profiles can be obtained, even during the bird migration season.

scholarly journals On the utility of individual tendency output: Revealing interactions between parameterised processes during a marine cold air outbreak

2021 ◽  
Author(s):  
Marvin Kähnert ◽  
Harald Sodemann ◽  
Wim C. de Rooy ◽  
Teresa M. Valkonen
Keyword(s):  
Prediction Models ◽  
Weather Prediction ◽  
Specific Humidity ◽  
Shallow Convection ◽  
Cold Air ◽  
Cold Air Outbreak ◽  
Order Of Magnitude ◽  
Underlying Causes ◽  
The Individual

AbstractForecasts of marine cold air outbreaks critically rely on the interplay of multiple parameterisation schemes to represent sub-grid scale processes, including shallow convection, turbulence, and microphysics. Even though such an interplay has been recognised to contribute to forecast uncertainty, a quantification of this interplay is still missing. Here, we investigate the tendencies of temperature and specific humidity contributed by individual parameterisation schemes in the operational weather prediction model AROME-Arctic. From a case study of an extensive marine cold air outbreak over the Nordic Seas, we find that the type of planetary boundary layer assigned by the model algorithm modulates the contribution of individual schemes and affects the interactions between different schemes. In addition, we demonstrate the sensitivity of these interactions to an increase or decrease in the strength of the parameterised shallow convection. The individual tendencies from several parameterisations can thereby compensate each other, sometimes resulting in a small residual. In some instances this residual remains nearly unchanged between the sensitivity experiments, even though some individual tendencies differ by up to an order of magnitude. Using the individual tendency output, we can characterise the subgrid-scale as well as grid-scale responses of the model and trace them back to their underlying causes. We thereby highlight the utility of individual tendency output for understanding process-related differences between model runs with varying physical configurations and for the continued development of numerical weather prediction models.

The impact of Secondary Ice Processes on a stratocumulus-to-cumulus transition during a Cold-Air Outbreak

2021 ◽  
Author(s):  
Michail Karalis ◽  
Georgia Sotiropoulou ◽  
Steven J. Abel ◽  
Elissavet Bossioli ◽  
Paraskevi Georgakaki ◽  
...  
Keyword(s):  
Prediction Models ◽  
Weather Prediction ◽  
Cumulus Clouds ◽  
Cold Air ◽  
Atmospheric Sciences ◽  
Boundary Layer Clouds ◽  
Cold Air Outbreak ◽  
Stratocumulus Clouds ◽  
Break Up ◽  
The Impact

<p>The representation of boundary layer clouds during marine Cold-Air Outbreaks (CAO) remains a great challenge for weather prediction models. Recent studies have shown that the representation of the transition from stratocumulus clouds to convective cumulus open cells largely depends on microphysical and precipitation processes, while Abel et al. (2017) further suggested that Secondary Ice Processes (SIP) may play a crucial role in the evolution of the cloud fields. In this study we use the Weather Research Forecasting model to investigate the impact of the most well-known SIP mechanisms (rime-splintering or Hallet-Mossop, mechanical break-up upon collisions between ice particles and drop-shattering) on a CAO case observed north of UK in 2013. While Hallet-Mossop is the only SIP process extensively implemented in atmospheric models, our results indicate that collisional break-up is also important in these conditions.</p><p> </p><p>Abel, S. J., Boutle, I. A., Waite, K., Fox, S., Brown, P. R. A., Cotton, R., Lloyd, G., Choularton, T. W., & Bower, K. N. (2017). The Role of Precipitation in Controlling the Transition from Stratocumulus to Cumulus Clouds in a Northern Hemisphere Cold-Air Outbreak, Journal of the Atmospheric Sciences, 74(7), 2293-2314. Retrieved Jan 9, 2021, from https://journals.ametsoc.org/view/journals/atsc/74/7/jas-d-16-0362.1.xml</p>

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