scholarly journals Atmospheric forcing of sea ice anomalies in the Ross Sea polynya region

2017 ◽  
Vol 11 (1) ◽  
pp. 267-280 ◽  
Author(s):  
Ethan R. Dale ◽  
Adrian J. McDonald ◽  
Jack H. J. Coggins ◽  
Wolfgang Rack
Keyword(s):  
Sea Ice ◽  
Ross Sea ◽  
Strong Wind ◽  
Ice Shelf ◽  
Sea Ice Concentration ◽  
Ross Ice Shelf ◽  
Wind Speeds ◽  
Brightness Temperatures ◽  
Wind Event ◽  
Wind Events

Abstract. We investigate the impacts of strong wind events on the sea ice concentration within the Ross Sea polynya (RSP), which may have consequences on sea ice formation. Bootstrap sea ice concentration (SIC) measurements derived from satellite SSM/I brightness temperatures are correlated with surface winds and temperatures from Ross Ice Shelf automatic weather stations (AWSs) and weather models (ERA-Interim). Daily data in the austral winter period were used to classify characteristic weather regimes based on the percentiles of wind speed. For each regime a composite of a SIC anomaly was formed for the entire Ross Sea region and we found that persistent weak winds near the edge of the Ross Ice Shelf are generally associated with positive SIC anomalies in the Ross Sea polynya and vice versa. By analyzing sea ice motion vectors derived from the SSM/I brightness temperatures we find significant sea ice motion anomalies throughout the Ross Sea during strong wind events, which persist for several days after a strong wind event has ended. Strong, negative correlations are found between SIC and AWS wind speed within the RSP indicating that strong winds cause significant advection of sea ice in the region. We were able to partially recreate these correlations using colocated, modeled ERA-Interim wind speeds. However, large AWS and model differences are observed in the vicinity of Ross Island, where ERA-Interim underestimates wind speeds by a factor of 1.7 resulting in a significant misrepresentation of RSP processes in this area based on model data. Thus, the cross-correlation functions produced by compositing based on ERA-Interim wind speeds differed significantly from those produced with AWS wind speeds. In general the rapid decrease in SIC during a strong wind event is followed by a more gradual recovery in SIC. The SIC recovery continues over a time period greater than the average persistence of strong wind events and sea ice motion anomalies. This suggests that sea ice recovery occurs through thermodynamic rather than dynamic processes.

scholarly journals Atmospheric forcing of sea ice anomalies in the Ross Sea Polynya region

2016 ◽  
Author(s):  
Ethan R. Dale ◽  
Adrian J. McDonald ◽  
Jack H.J. Coggins ◽  
Wolfgang Rack
Keyword(s):  
Wind Speed ◽  
Sea Ice ◽  
Ross Sea ◽  
Strong Wind ◽  
Sea Ice Concentration ◽  
Sea Ice Extent ◽  
Wind Speeds ◽  
Wind Event ◽  
Wind Events ◽  
Ice Production

Abstract. Despite warming trends in global temperatures, sea ice extent in the Southern Hemisphere has shown an increasing trend over recent decades. Wind-driven sea ice export from coastal polynyas is an important source of sea ice production. Areas of major polynyas in the Ross Sea, the region with largest increase in sea ice extent, have been suggested to produce a vast amount of the sea ice in the region. We investigate the impacts of strong wind events on the Ross Sea Polynyas and its sea ice concentration and possible consequences on sea ice production. We utilise Bootstrap sea ice concentration (SIC) measurements derived from satellite based, Special Sensor Microwave Imager (SSM/I) brightness temperatures. We compared these with surface winds and temperatures from automatic weather stations (AWS) of the University of Wisconsin-Madison Antarctic Meteorology Program. Our analysis focusses on the austral winter period defined as 1st April to 1st November in this study. Daily data were used to classified into characteristic regimes based on the percentiles of wind speed. For each regime, a composite of SIC anomaly was formed for the Ross Sea region. We found that persistent weak winds near the edge of the Ross Ice Shelf are generally associated with positive SIC anomalies in the Ross Sea Polynya (RSP). Conversely we found negative SIC anomalies in this area during persistent strong winds. By analysing sea ice motion vectors derived from SSM/I and SSMIS brightness temperatures, we find significant sea ice motion anomalies throughout the Ross Sea during strong wind events. These anomalies persist for several days after the strong wind event. Strong, negative correlations are found between SIC and AWS wind speed within the RSP indicating that strong winds cause significant advection of sea ice in the region. We were able to recreate these correlations using co-located ERA-Interim wind speeds. However when only days of a certain percentile based wind speed classification were used, the cross correlation functions produced by ERA-Interim wind speeds differed significantly from those produced using AWS wind speeds. The rapid decrease in SIC during a strong wind event is followed by a more gradual recovery in SIC. This increase occurs on a more gradual time scale than the average persistence of a strong wind event and the resulting sea ice motion anomalies, highlighting the production of new sea ice through thermodynamic processes. In the vicinity of Ross Island, ERA-Interim underestimates wind speeds by a factor of 1.7, which results in a significant misrepresentation of the impact of winds on polynya processes.

Impacts of strong surface winds on Antarctic Polynya

2020 ◽  
Author(s):  
Adrian McDonald
Keyword(s):  
Sea Ice ◽  
Ross Sea ◽  
Strong Wind ◽  
Surface Winds ◽  
Ice Shelf ◽  
Sea Ice Concentration ◽  
Ross Ice Shelf ◽  
Air Stream ◽  
Ice Concentration ◽  
Wind Events

<p>This study investigates the impacts of strong wind events on the sea ice concentration within polynya regions, with a focus on the Ross Sea Polynya (RSP). In particular, this work quantifies the sensitivity of sea ice concentrations to surface winds and whether there are threshold wind speeds required for regions of the polynya  to open up with subsequent impacts on air-sea heat fluxes. To analyse these processes, we examine version 3.1 of the Bootstrap sea ice concentration (SIC) satellite data set derived from SSM/I brightness temperatures and how they are connected to the surface winds from the ERA5 reanalysis over the period 1979 to 2018. While we examine these relationships around the entire Antarctic continent, we focus on the RSP and low-level jets in the Ross Sea. In particular, we examine how strong wind events which impact SIC in the RSP are linked to Ross Ice Shelf Air Stream events (strong low-level jets in the region). The hypothesis that the increase in Ross Ice Shelf Air Stream events, associated with a strengthening of the Amundsen Sea Low, has contributed to trends in sea ice production in this region is examined.</p>

scholarly journals Modeling the effect of Ross Ice Shelf melting on the Southern Ocean in quasi-equilibrium

2018 ◽  
Vol 12 (9) ◽  
pp. 3033-3044 ◽  
Author(s):  
Xiying Liu
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ross Sea ◽  
Global Ocean ◽  
Freshwater Flux ◽  
Quasi Equilibrium ◽  
Ice Shelf ◽  
Sea Ice Concentration ◽  
Ross Ice Shelf ◽  
Ice Concentration

Abstract. To study the influence of basal melting of the Ross Ice Shelf (BMRIS) on the Southern Ocean (ocean southward of 35∘ S) in quasi-equilibrium, numerical experiments with and without the BMRIS effect were performed using a global ocean–sea ice–ice shelf coupled model. In both experiments, the model started from a state of quasi-equilibrium ocean and was integrated for 500 years forced by CORE (Coordinated Ocean-ice Reference Experiment) normal-year atmospheric fields. The simulation results of the last 100 years were analyzed. The melt rate averaged over the entire Ross Ice Shelf is 0.25 m a−1, which is associated with a freshwater flux of 3.15 mSv (1 mSv = 103 m3 s−1). The extra freshwater flux decreases the salinity in the region from 1500 m depth to the sea floor in the southern Pacific and Indian oceans, with a maximum difference of nearly 0.005 PSU in the Pacific Ocean. Conversely, the effect of concurrent heat flux is mainly confined to the middle depth layer (approximately 1500 to 3000 m). The decreased density due to the BMRIS effect, together with the influence of ocean topography, creates local differences in circulation in the Ross Sea and nearby waters. Through advection by the Antarctic Circumpolar Current, the flux difference from BMRIS gives rise to an increase of sea ice thickness and sea ice concentration in the Ross Sea adjacent to the coast and ocean water to the east. Warm advection and accumulation of warm water associated with differences in local circulation decrease sea ice concentration on the margins of sea ice cover adjacent to open water in the Ross Sea in September. The decreased water density weakens the subpolar cell as well as the lower cell in the global residual meridional overturning circulation (MOC). Moreover, we observe accompanying reduced southward meridional heat transport at most latitudes of the Southern Ocean.

scholarly journals Case Study of a Barrier Wind Corner Jet off the Coast of the Prince Olav Mountains, Antarctica

2012 ◽  
Vol 140 (7) ◽  
pp. 2044-2063 ◽  
Author(s):  
Melissa A. Nigro ◽  
John J. Cassano ◽  
Matthew A. Lazzara ◽  
Linda M. Keller
Keyword(s):  
Strong Wind ◽  
Ice Shelf ◽  
Maximum Wind ◽  
Ross Ice Shelf ◽  
Wind Speeds ◽  
Wind Event ◽  
Transantarctic Mountains ◽  
Upper Level ◽  
Forcing Mechanisms

Abstract The Ross Ice Shelf airstream (RAS) is a barrier parallel flow along the base of the Transantarctic Mountains. Previous research has hypothesized that a combination of katabatic flow, barrier winds, and mesoscale and synoptic-scale cyclones drive the RAS. Within the RAS, an area of maximum wind speed is located to the northwest of the protruding Prince Olav Mountains. In this region, the Sabrina automatic weather station (AWS) observed a September 2009 high wind event with wind speeds in excess of 20 m s−1 for nearly 35 h. The following case study uses in situ AWS observations and output from the Antarctic Mesoscale Prediction System to demonstrate that the strong wind speeds during this event were caused by a combination of various forcing mechanisms, including katabatic winds, barrier winds, a surface mesocyclone over the Ross Ice Shelf, an upper-level ridge over the southern tip of the Ross Ice Shelf, and topographic influences from the Prince Olav Mountains. These forcing mechanisms induced a barrier wind corner jet to the northwest of the Prince Olav Mountains, explaining the maximum wind speeds observed in this region. The RAS wind speeds were strong enough to induce two additional barrier wind corner jets to the northwest of the Prince Olav Mountains, resulting in a triple barrier wind corner jet along the base of the Transantarctic Mountains.

scholarly journals Modelling Ross Ice Shelf melting effect on the Southern Ocean in quasi-equilibrium

2017 ◽  
Author(s):  
Xiying Liu
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ross Sea ◽  
Global Ocean ◽  
Freshwater Flux ◽  
Quasi Equilibrium ◽  
Ice Shelf ◽  
Local Circulation ◽  
Sea Ice Concentration ◽  
Ross Ice Shelf

Abstract. To study the influence of basal melting of Ross Ice Shelf (BMR) on the Southern Ocean (ocean southward of 35° S) in quasi-equilibrium, numerical experiments with and without BMR effect have been performed with a global ocean-sea ice-ice shelf coupled model. In both experiments, the model started from a state of quasi-equilibrium ocean and was integrated for 500 years forced by CORE (Coordinated Ocean-ice Reference Experiment) normal year atmospheric fields. The simulation results of the last 100 years have been analysed. It’s shown that, the melt rate averaged over the entire Ross Ice Shelf is 0.253 m/a, which is associated with a freshwater flux of 3.15 mSv (1 mSv = 103 m3/s). The extra freshwater flux decreases the salinity in the Southern Ocean substantially whereas the effect of concurrent heat flux is not so significant except in the middle layer of water body (roughly from 1500 m to 3000 m). The decreased density due to BMR effect creates local circulation anomalies in the Ross Sea and nearby water with the help of ocean bathymetry. Through advection by the Antarctic Circumpolar Current, the flux anomaly from BMR gives rise to the increase of sea ice thickness and sea ice concentration in the Ross Sea adjacent to the coast and the ocean water westward. The warm advection and downwelling associated with the local circulation anomalies decrease the sea ice concentration in the rim of sea ice cover adjacent to open water in the Ross Sea in September. The decreased density weakens the sub-polar cell as well as the lower cell in the global residual meridional overturning circulation. And, northward meridional heat transport anomaly in most latitudes of the global ocean is accompanied accordingly.

scholarly journals Impacts of strong wind events on sea ice and water mass properties in Antarctic coastal polynyas

2021 ◽  
Author(s):  
Xiaoqiao Wang ◽  
Zhaoru Zhang ◽  
Xuezhu Wang ◽  
Timo Vihma ◽  
Meng Zhou ◽  
...  
Keyword(s):  
Sea Ice ◽  
Mixed Layer Depth ◽  
Ocean Model ◽  
Offshore Wind ◽  
Katabatic Wind ◽  
Strong Wind ◽  
Surface Salinity ◽  
Sea Ice Concentration ◽  
Deep Layers ◽  
Wind Events

AbstractStrong offshore wind events (SOWEs) occur frequently near the Antarctic coast during austral winter. These wind events are typically associated with passage of synoptic- or meso-scale cyclones, which interact with the katabatic wind field and affect sea ice and oceanic processes in coastal polynyas. Based on numerical simulations from the coupled Finite Element Sea-ice Ocean Model (FESOM) driven by the CORE-II forcing, two coastal polynyas along the East Antarctica coast––the Prydz Bay Polynya and the Shackleton Polynya are selected to examine the response of sea ice and oceanic properties to SOWEs. In these polynyas, the southern or western flanks of cyclones play a crucial role in increasing the offshore winds depending on the local topography. Case studies for both polynyas show that during SOWEs, when the wind speed is 2–3 times higher than normal values, the offshore component of sea ice velocity can increase by 3–4 times. Sea ice concentration can decrease by 20–40%, and sea ice production can increase up to two to four folds. SOWEs increase surface salinity variability and mixed layer depth, and such effects may persist for 5–10 days. Formation of high salinity shelf water (HSSW) is detected in the coastal regions from surface to 800 m after 10–15 days of the SOWEs, while the HSSW features in deep layers exhibit weak response on the synoptic time scale. HSSW formation averaged over winter is notably greater in years with longer duration of SOWEs.

scholarly journals Heat Flux Sources Analysis to the Ross Ice Shelf Polynya Ice Production Time Series and the Impact of Wind Forcing

2019 ◽  
Vol 11 (2) ◽  
pp. 188
Author(s):  
Zian Cheng ◽  
Xiaoping Pang ◽  
Xi Zhao ◽  
Alfred Stein
Keyword(s):  
Heat Flux ◽  
Time Series ◽  
Wind Forcing ◽  
Strong Wind ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Wind Events ◽  
Ice Production ◽  
The Impact ◽  
Flux Component

The variation of Ross Ice Shelf Polynya (RISP) ice production is a synergistic result of several factors. This study aims to analyze the 2003–2017 RISP ice production time series with respect to the impact of wind forcing on heat flux sources. RISP ice production was estimated from passive microwave sea ice concentration images and reanalysis meteorological data using a thermodynamic model. The total ice production was divided into four components according to the amount of ice produced by different heat fluxes: solar radiation component (Vs), longwave radiation component (Vl), sensible heat flux component (Vfs), and latent heat flux component (Vfe). The results show that Vfs made the largest contribution, followed by Vl and Vfe, while Vs had a negative contribution. Our study reveals that total ice production and Vl, Vfs, and Vfe highly correlated with the RISP area size, whereas Vs negatively correlated with the RISP area size in October, and had a weak influence from April to September. Since total ice production strongly correlates with the polynya area and this significantly correlates with the wind speed of the previous day, strong wind events lead to sharply increased ice production most of the time. Strong wind events, however, may only lead to mildly increasing ice production in October, when enlarged Vs reduces the ice production. Wind speed influences ice production by two mechanisms: impact on polynya area, and impact on heat exchange and phase transformation of ice. Vfs and Vfe are influenced by both mechanisms, while Vs and Vl are only influenced by impact on polynya area. These two mechanisms show different degrees of influence on ice production during different periods. Persistent offshore winds were responsible for the large RISP area and high ice production in October 2005 and June 2007.

Latitudinal distribution of penguins, seals and whales observed during a late autumn transect through the Ross Sea

2004 ◽  
Vol 16 (3) ◽  
pp. 313-318 ◽  
Author(s):  
ROBERT P. VAN DAM ◽  
GERALD L. KOOYMAN
Keyword(s):  
Sea Ice ◽  
Marine Mammals ◽  
Ross Sea ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Emperor Penguins ◽  
Winter Foraging ◽  
Cruise Line ◽  
Abundance And Distribution ◽  
Adélie Penguins

During a cruise to the Ross Ice Shelf we counted all penguins and marine mammals seen whilst underway. Our objective was to determine the abundance and distribution of these animals along our cruise line. From 14 May until 11 June the sun was below the horizon. Our observations were from the 18 m high bridge. Most watches were in the dark, aided by the bridge spotlights. A total of 79 emperor penguins, 920 Adélie penguins, and 27 marine mammals were counted. We conclude that the Ross Sea, in which wildlife flourishes during the summer, is depauperate in winter. The low numbers of marine mammals may be due partially to their tendency to remain below the surface most of the time. However, Adélie penguins, a visual hunter which rests on sea ice at night, appear to prefer pack ice edges where there is a few hours of daylight and civil twilight for pursuit of prey. Non-breeding emperor penguins also rest on sea ice at night. All but four were observed north of the Ross Sea. Unlike more northerly colonies where females lay their egg and disperse in May female departure in the Ross Sea appears to be later and, we were unable to determine their winter foraging area.

scholarly journals A Strong Wind Event on the Ross Ice Shelf, Antarctica: A Case Study of Scale Interactions

2015 ◽  
Vol 143 (10) ◽  
pp. 4163-4180 ◽  
Author(s):  
Sheeba Nettukandy Chenoli ◽  
John Turner ◽  
Azizan Abu Samah
Keyword(s):  
Weather Prediction ◽  
Low Pressure ◽  
Strong Wind ◽  
Ice Shelf ◽  
Mountain Waves ◽  
Air Mass ◽  
Ross Ice Shelf ◽  
Wind Event ◽  
Mcmurdo Station ◽  
Mesoscale Low

Abstract In situ observations, satellite imagery, numerical weather prediction, and reanalysis fields are used to investigate the synoptic and mesoscale environment of a strong wind event (SWE) at McMurdo Station/Ross Island region on the Ross Ice Shelf, Antarctica, on 10 October 2003. The SWE occurred during the passage of a sequence of three mesoscale low pressure systems from the central Ross Ice Shelf to the southwest Ross Sea. A potential vorticity (PV) analysis showed that the lows drew air of continental origin down the glacial valleys of the Transantarctic Mountains and onto the ice shelf as a katabatic drainage flow. However, the analysis indicated that the air mass associated with the SWE was of recurved maritime origin drawn in by the second mesoscale low (L2). This air mass approached McMurdo Station from the south where interactions with the orography played a critical role. In the early stages of the event, when the wind speed was less than 10 m s−1, the air was deflected around the topographical features, such as Minna Bluff and Black and White Islands. As the pressure gradient increased, winds of more than 10 m s−1 crossed the orography and developed mountain waves along the lee slopes. When the Froude number became larger than 1, large-amplitude vertically propagating mountain waves developed over the McMurdo Station/Ross Island area, increasing the wind to 16 m s−1. The reanalysis fields did not resolve the mesoscale lows; however, the Antarctic Mesoscale Prediction System (AMPS) model was able to simulate important characteristics of the SWE such as the mesoscale low pressure system, flow around the topographical barrier, and the mountain wave.

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