Role of air-mass transformations in exchange between the Arctic and mid-latitudes

Pithan, Felix; Svensson, Gunilla; Caballero, Rodrigo; Chechin, Dmitry; Cronin, Timothy W.; Ekman, Annica M. L.; Neggers, Roel; Shupe, Matthew D.; Solomon, Amy; Tjernström, Michael; Wendisch, Manfred

doi:10.1038/s41561-018-0234-1

Cited by 146 publications

(162 citation statements)

References 103 publications

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“…; Bauer and Jung, ; Pithan et al . ) and difficulties in estimating the surface emission in the forward model over snow and sea ice for satellite data. In particular, the microwave surface emission is more variable over snow and sea ice, and there are assumptions in the modelling of this that are likely to be inaccurate (e.g., specular reflection; Guedj et al .…”

Section: Introductionmentioning

confidence: 99%

Use and impact of Arctic observations in the ECMWF Numerical Weather Prediction system

Lawrence

Bormann

Sandu

et al. 2019

Quart J Royal Meteoro Soc

111

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This paper presents an assessment of the usage of Arctic atmospheric observations in the Numerical Weather Prediction (NWP) system of the European Centre for Medium‐Range Weather Forecasts, and of their impact on the quality of short‐ to medium‐range forecasts. The Arctic has low coverage of conventional data north of 70°N but one of the highest levels of coverage of satellite sounding data on Earth. The impact of Arctic observations on forecast skill was assessed by performing Observing System Experiments, in which different observation types were removed from the full observing system. This assessment was complemented by an analysis of Forecast Sensitivity to Observation Impact diagnostics. To our knowledge it is the first time that comprehensive numerical experimentation has been carried out to explore the role of different Arctic observations in a state‐of‐the‐art global operational NWP system. All Arctic observations were found to have a positive impact on forecast skill in the Arctic region, with the greatest tropospheric impacts on both short‐ and medium‐range forecasts due to microwave, conventional and infrared sounding observations. Results indicate the great importance of microwave sounding data and conventional data, which are found to be the key observing systems in the summer and winter seasons, respectively. These observations were found to have positive and statistically significant impacts on forecasts not only in the Arctic but also in the midlatitude regions at longer lead times. Differences between the seasons are most likely due to problems assimilating microwave sounding observations over snow and sea ice, leading to a reduced impact in winter. There is also the suggestion of increased importance of conventional data in winter, and other factors may also play a role.

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Section: Introductionmentioning

confidence: 99%

Use and impact of Arctic observations in the ECMWF Numerical Weather Prediction system

Lawrence

Bormann

Sandu

et al. 2019

Quart J Royal Meteoro Soc

111

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“…Pithan et al (2018) concluded that more observations and model experiments following air masses on their paths to the Arctic are needed to improve our understanding of Arctic air mass transformation. Previous modeling studies of this problem have been conducted with 1‐dimensional column models or 2‐dimensional cloud‐resolving models (Cronin et al, 2017; Cronin & Tziperman, 2015; Pithan et al, 2014, 2016), but never to our knowledge with a full 3‐dimensional large eddy simulation (LES).…”

Section: Introductionmentioning

confidence: 99%

“…Arctic air mass transformation is the process whereby relatively warm, moist, mid-latitude air is advected over the Arctic pack ice, cools radiatively, and eventually transforms into a polar air mass characterized by low humidity and a strong surface-based inversion (Cronin et al, 2017;Cronin & Tziperman, 2015;Curry, 1983;Pithan et al, 2014Pithan et al, , 2016Pithan et al, , 2018Wexler, 1936). Rapid and strong intrusions of warm and moist air to the Arctic occurs about 16 times every winter season (October to January) and the frequency has increased in December and January during the period 1990 to 2012 (Woods & Caballero, 2016).…”

Section: Introductionmentioning

confidence: 99%

A Sensitivity Study of Arctic Air‐Mass Transformation Using Large Eddy Simulation

et al. 2020

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Arctic air mass transformation is linked to the evolution of low‐level mixed‐phase clouds. These clouds can alter the structure of the boundary layer and modify the surface energy budget. In this study, we use three‐dimensional large eddy simulation and a bulk sea ice model to examine the lifecycle of clouds formed during wintertime advection of moist and warm air over sea ice, following a Lagrangian perspective. We investigate the stages of cloud formation, evolution, and decay. The results show that radiative cooling at the surface gives rise to fog formation which subsequently rises and transforms into a mixed‐phase cloud. In our baseline simulation, the cloud persists for about 5 days and increases the surface temperature by on average 17 °C. Sensitivity tests show that the lifetime of the cloud is sensitive to changes in the vapor supply at cloud top. This flux is mainly impacted by changes in the divergence rate; an imposed convergence decreases the lifetime to 2 days while an imposed large‐scale divergence increases the lifetime to more than 6 days. The largest difference in cloud radiative properties is found in the experiment with increased ice crystal number concentrations. In this case, the lifetime of the cloud is similar compared to baseline but the amount of liquid water is clearly depleted throughout the whole cloud sequence and the surface temperature is on average 6 °C cooler. The cloud condensation nuclei concentration has a weaker effect on the radiative properties and lifetime of the cloud.

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“…Consequently, CAO air masses are rapidly transformed from anomalously cold and dry into much warmer and moist air masses. This can lead to vigorous convective overturning and the release of latent heat during cloud formation (see review by Pithan et al, , and references therein). At the same time, the surface heat fluxes cool the ocean's mixed layer; in fact, CAOs deliver the bulk of the wintertime heat flux forcing of the Nordic Seas (Papritz & Spengler, ) and are the key driver for ocean convection at the northernmost extremity of the Atlantic Meridional Overturning Circulation (Buckley & Marshall, ; Marshall & Schott, ).…”

Section: Introductionmentioning

confidence: 99%

On the Thermodynamic Preconditioning of Arctic Air Masses and the Role of Tropopause Polar Vortices for Cold Air Outbreaks From Fram Strait

et al. 2019

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Fram Strait is a hot spot of Arctic cold air outbreaks (CAOs), which typically occur within the northerly flow associated with a strong low tropospheric east‐west pressure gradient between Svalbard and Greenland. This study investigates the processes in the inner Arctic that thermodynamically precondition air masses associated with CAOs south of Fram Strait where they lead to negative potential temperature anomalies often in excess of 15 K. Kinematic backward trajectories from Fram Strait are used to quantify the Arctic residence time and to analyze the thermodynamic evolution of these air masses. Additionally, the study explores the importance of cyclonic tropopause polar vortices (TPVs) for CAO formation south of Fram Strait. Results from a detailed case study and the climatological analysis of the 100 most intense CAOs from Fram Strait in the ERA‐Interim period reveal that (i) air masses that cause CAOs (CAO air masses) reside longer in the inner Arctic compared to those that do not (NO‐CAO air masses), and they originate from climatologically colder regions; (ii) the 10‐day accumulated cooling is very similar for CAO and NO‐CAO air masses indicating that the transport history and northerly origin of the air masses is more decisive for the formation of an intense negative temperature anomaly south of Fram Strait than an enhanced inner Arctic diabatic cooling; (iii) 40% (29%) of the top 40 (100) CAOs are related to a TPV in the vicinity of Fram Strait; (iv) TPVs confine anomalously cold air masses within their associated low tropospheric cold dome leading to enhanced accumulated radiative cooling.

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Role of air-mass transformations in exchange between the Arctic and mid-latitudes

Cited by 146 publications

References 103 publications

Use and impact of Arctic observations in the ECMWF Numerical Weather Prediction system

Use and impact of Arctic observations in the ECMWF Numerical Weather Prediction system

A Sensitivity Study of Arctic Air‐Mass Transformation Using Large Eddy Simulation

On the Thermodynamic Preconditioning of Arctic Air Masses and the Role of Tropopause Polar Vortices for Cold Air Outbreaks From Fram Strait

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