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This report reviews 2012-2013 field season activities of the University of Wisconsin-Madison's Antarctic Automatic Weather Station (AWS) program, summarizes the science that these sites are supporting, and outlines the factors that impact the number of AWS sites serviced in any given field season. The 2012-2013 austral summer season was unusual in the AWS network history. Challenges encountered include, but are not limited to, warmer than normal conditions in the Ross Island area impacting airfield operations, changes to logistical procedures, and competition for shared resources. A flexible work plan provides the best means for taking on these challenges while maximizing AWS servicing efforts under restricted conditions and meeting the need for routine servicing that maintaining an autonomous observing network demands. [ABSTRACT FROM AUTHOR]

Atmospheric measurements taken over the span of an entire year between October 2019 and September 2020 during the icebreaker-based Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition provide insight into processes acting in the Arctic atmosphere. Through the merging of disparate, yet complementary in situ observations, we can derive information about these thermodynamic and kinematic processes with great detail. This paper describes methods used to create a lower atmospheric properties dataset containing information on several key features relating to the central Arctic atmospheric boundary layer, including properties of temperature inversions, low-level jets, near-surface meteorological conditions, cloud cover, and the surface radiation budget. The lower atmospheric properties dataset was developed using observations from radiosondes launched at least four times per day, a 10 m meteorological tower and radiation station deployed on the sea ice near the Research Vessel Polarstern, and a ceilometer located on the deck of the Polarstern. This lower atmospheric properties dataset, which can be found at *insert DOI when published*, contains metrics which fall into the overarching categories of temperature, wind, stability, clouds, and radiation at the time of each radiosonde launch. The purpose of the lower atmospheric properties dataset is to provide a consistent description of general atmospheric boundary layer conditions throughout the MOSAiC year which can aid in research applications with the overall goal of gaining a greater understanding of the atmospheric processes governing the central Arctic and how they may contribute to future climate change. [ABSTRACT FROM AUTHOR]

Small Unmanned Meteorological Observer (SUMO) unmanned aerial vehicles (UAVs) were used to observe atmospheric boundary layer temperature profiles in the vicinity of McMurdo Station, Antarctica during January and September 2012. The observations from four flight days are shown and exhibit a variety of boundary layer temperature profiles ranging from deep, well-mixed conditions to strong, shallow inversions. Repeat UAV profiles over short periods of time (tens of minutes to several hours) revealed rapid changes in boundary layer structure. The success of the SUMO flights described here demonstrates the potential for using small UAVs for Antarctic research. [ABSTRACT FROM AUTHOR]

There is growing recognition that reductions in Arctic sea ice extent will influence patterns of atmospheric circulation both within and beyond the Arctic. We explore the impact of 2007 ice conditions (the second lowest Arctic sea ice extent in the satellite era) on atmospheric circulation and surface temperatures and fluxes through a series of model experiments with the NCAR Community Atmospheric Model version 3 ( CAM3). Two 30-year simulations were performed; one using climatological sea ice extent for the end of the 20th century and other using observed sea ice extent from 2007. Circulation differences over the Northern Hemisphere were most prominent during autumn and winter with lower sea level pressure ( SLP) and tropospheric pressure simulated over much of the Arctic for the 2007 sea ice experiment. The atmospheric response to 2007 ice conditions was much weaker during summer, with negative SLP anomalies simulated from Alaska across the Arctic to Greenland. Higher temperatures and larger surface fluxes to the atmosphere in areas of anomalous open water were also simulated. CAM3 experiment results were compared to observed SLP anomalies from the National Center for Environmental Prediction/National Center for Atmospheric Research ( NCEP/ NCAR) Reanalysis data. The observed SLP anomalies during spring are nearly opposite to those simulated. In summer, large differences were shown between the observed and simulated SLP also, suggesting that the sea ice conditions in the months preceding and during the summer of 2007 were not responsible for creating an atmospheric circulation pattern which favoured the large observed sea ice loss. The simulated and observed atmospheric circulation anomalies during autumn and winter were more similar than spring and summer, with the exception of a strong high pressure system in the Beaufort Sea which was not simulated, suggesting that the forced atmospheric response to reduced sea ice was in part responsible for the observed atmospheric circulation anomalies during autumn and winter. [ABSTRACT FROM AUTHOR]

The article focuses on an observational study of local temperature variation by mounting on a bicycle a weather station, the Kestrel 4000 of Nielsen-Kellerman, in the vicinity of Boulder, Colorado. Topics discussed include the use of global positioning system (GPS) unit to georeference the data from the Kestrel, antrophogenic and topographic factors in controlling local temperature, and the use of bicycle-based meteorological instrumentation as an educational tool in the study of atmospheric science.

Spectral (interior) nudging is a way of constraining a model to be more consistent with observed behavior. However, such control over model behavior raises concerns over how much nudging may affect unforced variability and extremes. Strong nudging may reduce or filter out extreme events since nudging pushes the model toward a relatively smooth, large-scale state. The question then becomes: what is the minimum spectral nudging needed to correct biases while not limiting the simulation of extreme events? To determine this, case studies were performed using a six-member ensemble of the Pan-Arctic Weather Research and Forecasting model (WRF) with varying spectral nudging strength, using WRF's standard nudging as a reference point. Two periods were simulated, one in a cold season (January 2007) and one in a warm season (July 2007). Precipitation and 2-m temperature were analyzed to determine how changing spectral nudging strength impacts temperature and precipitation extremes and selected percentiles. Results suggest that there is a marked lack of sensitivity to varying degrees of nudging. Moreover, given that nudging is an artificial forcing applied in the model, an outcome of this work is that nudging strength can be considerably smaller than the WRF standard strength and still produce climate simulations that are much better than using no nudging. [ABSTRACT FROM AUTHOR]

The article discusses the progress related to the Antarctic Mesoscale Prediction System (AMPS) since it was launched in 2000. It explains that AMPS is a real-time numerical weather prediction system for Antarctica that uses the Weather Research and Forecasting (WRF) model. It highlights the evolution in the role of AMPS to support the logistical and biological needs of international users.

Antarctica boasts one of the world's harshest environments. Since the earliest expeditions, a major challenge has been to characterize the surface meteorology around the continent. In 1980, the University of Wisconsin--Madison (UW-Madison) took over the U.S. Antarctic Program (USAP) Automatic Weather Station (AWS) program. Since then, the UW-Madison AWS network has aided in the understanding of unique Antarctic weather and climate. This paper summarizes the development of the UW-Madison AWS network, issues related to instrumentation and data quality, and some of the ways these observations have and continue to benefit scientific investigations and operational meteorology. [ABSTRACT FROM AUTHOR]

Continental temperature inversions significantly influence air quality, yet little is known about their variability in frequency and intensity with time or sensitivity to dynamical changes with climate. Inversion statistics for six upper-air stations in the American Southwest are derived for the period 1994--2008 from radiosonde data reported by the Global Telecommunication System (GTS) and National Climatic Data Center (NCDC), which use different significant level standards. GTS data indicate that low-level elevated inversions have increased in frequency at four of six sites, consistent with enhanced regional stagnation projected by models. NCDC data, in contrast, show remarkable declines in weak, near-surface inversions through 2001, indicating local surface conditions may counteract atmospheric dynamics in regulating inversion activity and air quality. To further test the sensitivity of inversion activity to climate, associations between wintertime inversion frequency and large-scale circulation are quantified using the self-organizing map technique. Twenty-four representative circulation patterns are derived from North American Regional Reanalysis (NARR) 500-hPa geopotential height fields, and these patterns are correlated with inversion frequency at each site. Inversion activity in Salt Lake City, Utah, and Albuquerque and Santa Teresa, New Mexico, is found to correspond well with large-scale anticyclonic ridging; however, sensitivities to large-scale circulation in Denver, Colorado, and Flagstaff and Tucson, Arizona, are weak. Denver stands out in exhibiting a higher percentage of near-surface inversions in winter than the other southwestern sites. These findings indicate that dynamical changes with climate will not uniformly influence inversions and hence urban air quality conditions in the American Southwest. [ABSTRACT FROM AUTHOR]

In September 2009, the first unmanned aerial vehicles were flown over Terra Nova Bay, Antarctica, to collect information regarding air--sea interactions. Prior to the field season, wind and temperature data from a local automatic weather station (AWS) were collected from 1993 to 2007 and compared with an August--October 2006--08 satellite cyclone analysis to place the September 2009 observations into a broader context. AWS wind data revealed a strong tendency toward downslope flow in the region regardless of season, as the majority (55%%) of winds were from the west to northwesterly directions. Most winds observed at the site were less than 20 m s−−1, but 83%% of the stronger winds were associated with downslope flow. Of 15 strong wind events (greater than 20 m s−−1 for more than 10 h) evaluated during the cyclone analysis period, 100%% occurred in the presence of a cyclone in the adjacent Ross Sea. Winter experienced the greatest number of strong wind events (68%%), and summer had the least (4%%). Most temperatures were between −−15°° and −−25°°C, with temperatures influenced by wind fluctuations. The cyclone analysis revealed that 64%% of systems were comma shaped, and most cyclones (84%%) within the Ross Sea were mesocyclones. A comparison of AWS data for Septembers 1993--2007 and September 2009 showed more strong wind events during 2009, while the cyclone analysis revealed a shift in cyclonic activity eastward. Reanalysis data comparing September 1993--2007 and September 2009 show an eastward shift in a deeper upper-level trough, indicating that September 2009 was an anomalous year. [ABSTRACT FROM AUTHOR]

The article focuses on a study which analyzed the relationship between near-surface atmospheric circulation and precipitation in the Mackenzie and Yukon River basins. Using self-organizing maps, a climatology of sea level pressure patterns based on ERA40 reanalysis was developed. Near-surface atmospheric patterns in the region and low-pressure patterns over land areas and the Beaufort/Chuckchi Seas in the summer was analyzed.

Spatial and temporal changes in high-latitude moisture convergence simulated by the National Center for Atmospheric Research Community Climate System Model, version 3 (CCSM3) are investigated. Moisture convergence is calculated using the aerological method with model fields of specific humidity and winds spanning the periods from 1960 to 1999 and 2070 to 2089. The twenty-first century incorporates the A2 scenario from the Special Report on Emissions Scenarios. The model’s realism in reproducing the twentieth-century moisture convergence is evaluated by comparison with values derived from the 40-yr ECMWF Re-Analysis (ERA-40). In the area north of 75°N, the simulated moisture convergence is similar to observations during summer, but it is larger in winter, spring, and autumn. The model also underestimates (overestimates) the mean annual moisture convergence in the eastern (western) Arctic. Late twenty-first century annual, seasonal, and regional changes are determined by applying a self-organizing map technique to the model’s sea level pressure fields to identify dominant atmospheric circulation regimes and their corresponding moisture convergence fields. Changes in moisture convergence from the twentieth to the twenty-first century result primarily from thermodynamic effects (∼70%), albeit shifts in the frequency of dominant circulation patterns exert a relatively large influence on future changes in the eastern Arctic. Increased moisture convergence in the central Arctic (North Atlantic) stems mainly from thermodynamic changes in summer (winter). Changes in the strength and location of poleward moisture gradients are most likely responsible for projected variations in moisture transport, which are in turn a consequence of increasing anthropogenic greenhouse gas emissions as prescribed by the A2 scenario. [ABSTRACT FROM AUTHOR]

Meridonal moisture transport into the Arctic derived from one simulation of the National Center for Atmospheric Research Community Climate System Model (CCSM3), spanning the periods of 1960–99, 2010–30, and 2070–89, is analyzed. The twenty-first-century simulation incorporates the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 scenario for CO2 and sulfate emissions. Modeled and observed [from the 40-yr ECMWF Re-Analysis (ERA-40)] sea level pressure (SLP) fields are classified using a neural network technique called self-organizing maps to distill a set of characteristic atmospheric circulation patterns over the region north of 60°N. Model performance is validated for the twentieth century by comparing the frequencies of occurrence of particular circulation regimes in the model to those from the ERA-40. The model successfully captures dominant SLP patterns, but differs from observations in the frequency with which certain patterns occur. The model’s twentieth-century vertical mean moisture transport profile across 70°N compares well in terms of structure but exceeds the observations by about 12% overall. By relating moisture transport to a particular circulation regime, future changes in moisture transport across 70°N are assessed and attributed to changes in frequency with which the atmosphere resides in particular SLP patterns and/or to other factors, such as changes in the meridional moisture gradient. By the late twenty-first century, the transport is projected to increase by about 21% in this model realization, with the largest contribution (32%) to the total change occurring in summer. Only about one-quarter of the annual increase is due to changes in pattern occupancy, suggesting that the majority is related to mainly thermodynamic factors. A larger poleward moisture transport likely constitutes a positive feedback on the system through related increases in latent heat release and the emission of longwave radiation to the surface. [ABSTRACT FROM AUTHOR]

The article discusses the stimulations of regional circulation and hydroclimatology from fourteen general circulation models (GCMs) in Eurasia. It notes that GCMs tend to either over- or under-emphasize the strength and persistence of winter storms in the continent, affecting the hydroclimatology of watersheds. Furthermore, it cites the trends in 20th century precipitation in relation to greenhouse gas induced climate change.

Analysis of the synoptic climatology and precipitation patterns over the North Atlantic region allows for a better understanding of the atmospheric input to the mass balance of the Greenland ice sheet. The self-organizing map (SOM) technique was applied to the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) daily sea level pressure (SLP) data from 1961 to 1999 to objectively identify synoptic SLP patterns over the North Atlantic region. A total of 35 different SLP patterns were identified. Patterns common to the winter season are characterized by deep low pressure systems that approach Greenland through an active North Atlantic storm track, whereas patterns most common to the summer months are generally weaker and approach the ice sheet from the west through Baffin Bay. The blocking, splitting, and intensification of cyclones by the high elevations of the Greenland ice sheet were identified in this analysis. Analysis of ERA-40 precipitation associated with each SLP pattern revealed that the largest precipitation events were associated with passing cyclones that created onshore flow, allowing the air to be lifted orographically by the steep margins of the ice sheet. The ERA-40 annual mean precipitation over Greenland from 1961 to 1999 was 35.8 cm yr-1. Greenland was divided into five subregions, and the preferred synoptic patterns for receiving precipitation in each region include cyclones positioned to allow dynamic and orographic lift in each region. Annual precipitation contributions from each SLP pattern were isolated to reveal that half of the annual mean precipitation over Greenland comes from only 11 of the 35 identified synoptic patterns (31.4%), highlighting the importance of studying Greenland precipitation on an event-by-event basis on a daily time scale. [ABSTRACT FROM AUTHOR]

An analysis of the surface wind field across the Ross Ice Shelf, Antarctica, is conducted for austral autumn 2005. The airflow is divided into dominant wind regimes identifying similar wind patterns and the associated typical atmospheric forcing. The results of previous research and a seasonal analysis of the recently expanded network of automatic weather stations in the Ross Ice Shelf region are used to define the dominant wind regimes. Events composing each wind regime are identified by matching wind speed and wind direction observations at several automatic weather station sites for durations of at least 10 h. The four different dominant wind regimes are barrier wind, strong katabatic, weak katabatic, and light wind. Each wind regime is studied through the use of wind rose plots and sea level pressure fields from the Antarctic Mesoscale Prediction System. The sea level pressure fields are used to characterize the forcing of the surface wind field by synoptic pressure gradients. The four dominant wind regimes result in classifying less than 50% of the total hours for austral autumn 2005. The results indicate that previous studies of the Ross Ice Shelf surface wind field, focusing on katabatic winds and barrier winds, represent less than one-half of the observed winds. This study provides a better understanding of the composition of the surface wind field in Antarctica and more insight into the characteristics of the Ross Ice Shelf airstream. [ABSTRACT FROM AUTHOR]

The coastal geography of Barrow, Alaska, makes the city vulnerable to weather events that cause flooding and erosion. This study uses the self-organizing map (SOM) algorithm, an unsupervised learning process that codifies large, multivariate datasets onto a 2-dimensional array, or map, to study large-scale circulation patterns associated with temperature and high wind extremes at Barrow. The analysis first uses the SOM algorithm to produce an automated 55 yr synoptic climatology of daily sea level pressure patterns for the western Arctic for August to November, when the area is potentially ice free. The results are in agreement with previous Arctic climatologies, showing the Aleutian Low to be dominant in southern Alaska, and high pressure prevalent over the Beaufort and Chukchi Seas. The SOM algorithm is then used to study circulation patterns associated with temperature and high wind extremes at Barrow. These results show that high winds are associated with patterns containing a strong pressure gradient between the Aleutian Low and the Beaufort and Chukchi Seas and also with patterns that contain a low pressure system to the north of Barrow. High (low) air temperature extreme anomalies are associated with patterns that produce strong, southerly (northerly) air flow at Barrow. This study demonstrates the utility of using SOMs to investigate the relationship between local weather conditions and large-scale patterns. This approach can be applied to future global climate model (GCM) simulations to investigate the impact of changes in large-scale circulation patterns to local extreme events. [ABSTRACT FROM AUTHOR]

During the 42-year period (1979–2020) of satellite measurements, four major winter (December–March) polynyas have been observed north of Greenland: one in December 1986 and three in the last decade, i.e., February of 2011, 2017, and 2018. The 2018 polynya was unparalleled in its magnitude and duration compared to the three previous events. Given the apparent recent increase in the occurrence of these extreme events, this study aims to examine their evolution and causality, in terms of forced versus natural variability. The limited weather station and remotely sensed sea ice data are analyzed combining with output from the fully coupled Regional Arctic System Model (RASM), including one hindcast and two ensemble simulations. We found that neither the accompanying anomalous warm surface air intrusion nor the ocean below had an impact (i.e., no significant ice melting) on the evolution of the observed winter open-water episodes in the region. Instead, the extreme atmospheric wind forcing resulted in greater sea ice deformation and transport offshore, accounting for the majority of sea ice loss in all four polynyas. Our analysis suggests that strong southerly winds (i.e., northward wind with speeds greater than 10 m s -1) blowing persistently over the study region for at least 2 d or more were required over the study region to mechanically redistribute some of the thickest Arctic sea ice out of the region and thus to create open-water areas (i.e., a latent heat polynya). To assess the role of internal variability versus external forcing of such events, we carried out and examined results from the two RASM ensembles dynamically downscaled with output from the Community Earth System Model (CESM) Decadal Prediction Large Ensemble (DPLE) simulations. Out of 100 winters in each of the two ensembles (initialized 30 years apart: one in December 1985 and another in December 2015), 17 and 16 winter polynyas were produced north of Greenland, respectively. The frequency of polynya occurrence had no apparent sensitivity to the initial sea ice thickness in the study area pointing to internal variability of atmospheric forcing as a dominant cause of winter polynyas north of Greenland. We assert that dynamical downscaling using a high-resolution regional climate model offers a robust tool for process-level examination in space and time, synthesis with limited observations, and probabilistic forecasts of Arctic events, such as the ones being investigated here and elsewhere. [ABSTRACT FROM AUTHOR]

The article reflects on the six priorities for the southern polar research convened by the Scientific Committee on Antarctic Research (SCAR) in April 2014. Topics discussed include defining the role of interactions between the atmosphere, ocean and ice in controlling the rate of climate change, impact of changes on ocean's ability to absorb heat and carbon dioxide and mitigation of human activities for the effective Antarctic regulation. Also discusses evolution and survival of Antarctic life.

Surface, upper‐air, and radar observations are used to assess the performance of the Antarctic Mesoscale Prediction System (AMPS) in simulating the mesoscale aspects of a wind and precipitation event over the Ross Island region of Antarctica that spanned January 16–20, 2016. The observations, collected during the Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE), provide a unique dataset for evaluating AMPS, especially the radar observations that facilitate a three‐dimensional depiction of winds and precipitation. Comparisons of AMPS forecast data with surface meteorology, balloon‐sounding, and profiling radar observations at and above sites near McMurdo Station reveal a mixture of similarities and differences. A generally southerly flow is evident at low levels in both the AMPS simulations and observed Doppler radial velocities. AMPS winds are comparable to those observed at the surface and aloft in terms of magnitude, direction, and timing but the strongest simulated southerly flow is displaced eastward relative to the observations. AMPS‐simulated reflectivity over the broader Ross Island region is more limited in areal extent and smaller in magnitude than observed by a scanning Doppler radar. Three episodes of surface precipitation are observed near McMurdo Station over the five‐day event with peak rates of ∼3 mm h−1 and a total accumulation of ∼22 mm. However, AMPS produces no surface precipitation at that location over the five‐day event due to a low‐level dry bias in the forecasts. The results show the first observationally based three‐dimensional understanding of meteorology in the Ross Island region. [ABSTRACT FROM AUTHOR]

An automated method to classify Arctic fog into distinct thermodynamic profiles using historic in-situ surface and upper-air observations is presented. This classification is applied to low-resolution Integrated Global Radiosonde Archive (IGRA) soundings and high-resolution Arctic Summer Cloud Ocean Study (ASCOS) soundings in low- and high-Arctic coastal and pack-ice environments. Results allow investigation of fog macrophysical properties and processes in coastal East Greenland during melt seasons 1980-2012. Integrated with fog observations from three synoptic weather stations, 422 IGRA soundings are classified into six fog thermodynamic types based on surface saturation ratio, type of temperature inversion, fog-top height relative to inversion-base height and stability using the virtual potential temperature gradient. Between 65-80% of fog observations occur with a low-level inversion, and statically neutral or unstable surface layers occur frequently. Thermodynamic classification is sensitive to the assigned dew-point depression threshold, but categorization is robust. Despite differences in the vertical resolution of radiosonde observations, IGRA and ASCOS soundings yield the same six fog classes, with fog-class distribution varying with latitude and environmental conditions. High-Arctic fog frequently resides within an elevated inversion layer, whereas low-Arctic fog is more often restricted to the mixed layer. Using supplementary time-lapse images, ASCOS microwave radiometer retrievals and airmass back-trajectories, we hypothesize that the thermodynamic classes represent different stages of advection fog formation, development, and dissipation, including stratus-base lowering and fog lifting. This automated extraction of thermodynamic boundary-layer and inversion structure can be applied to radiosonde observations worldwide to better evaluate fog conditions that affect transportation and lead to improvements in numerical models. [ABSTRACT FROM AUTHOR]

Accurately predicting moisture and stability in the Antarctic planetary boundary layer (PBL) is essential for low-cloud forecasts, especially when Antarctic forecasters often use relative humidity as a proxy for cloud cover. These forecasters typically rely on the Antarctic Mesoscale Prediction System (AMPS) Polar Weather Research and Forecasting (Polar WRF) Model for high-resolution forecasts. To complement the PBL observations from the 30-m Alexander Tall Tower! (ATT) on the Ross Ice Shelf as discussed in a recent paper by Wille and coworkers, a field campaign was conducted at the ATT site from 13 to 26 January 2014 using Small Unmanned Meteorological Observer (SUMO) aerial systems to collect PBL data. The 3-km-resolution AMPS forecast output is combined with the global European Centre for Medium-Range Weather Forecasts interim reanalysis (ERAI), SUMO flights, and ATT data to describe atmospheric conditions on the Ross Ice Shelf. The SUMO comparison showed that AMPS had an average 2-3 m s−1 high wind speed bias from the near surface to 600 m, which led to excessive mechanical mixing and reduced stability in the PBL. As discussed in previous Polar WRF studies, the Mellor-Yamada-Janjić PBL scheme is likely responsible for the high wind speed bias. The SUMO comparison also showed a near-surface 10-15-percentage-point dry relative humidity bias in AMPS that increased to a 25-30-percentage-point deficit from 200 to 400 m above the surface. A large dry bias at these critical heights for aircraft operations implies poor AMPS low-cloud forecasts. The ERAI showed that the katabatic flow from the Transantarctic Mountains is unrealistically dry in AMPS. [ABSTRACT FROM AUTHOR]

Highlights the Antarctic Weather Forecasting Workshop (AWFW) held at Byrd Polar Research Center in Ohio State University in Ohio. Topics discussed in the workshop; State of operational weather forecasting in the Antarctic; Recommendations from the workshop.

Evaluates wintertime Antarctic boundary layer winds by the United States National Centers for Environmental Prediction-National Center for Atmospheric Center global reanalysis program. Importance of katabatic and synoptic forces in shaping winter winds; Adjustment of ambient pressure gradient to the continental orography.

During the winter of 2019/2020, as the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) project started its work, the Arctic Oscillation (AO) experienced some of its largest shifts, ranging from a highly negative index in November 2019 to an extremely positive index during January–February–March (JFM) 2020. The permanent positive AO phase for the 3 months of JFM 2020 was accompanied by a prevailing positive phase of the Arctic Dipole (AD) pattern. Here we analyze the sea ice thickness (SIT) distribution based on CryoSat-2/SMOS satellite-derived data augmented with results from the hindcast simulation by the fully coupled Regional Arctic System Model (RASM) from November 2019 through March 2020. A notable result of the positive AO phase during JFM 2020 was large SIT anomalies of up to 1.3 m that emerged in the Barents Sea (BS), along the northeastern Canadian coast and in parts of the central Arctic Ocean. These anomalies appear to be driven by nonlinear interactions between thermodynamic and dynamic processes. In particular, in the Barents and Kara seas (BKS), they are a result of enhanced ice growth connected with low-temperature anomalies and the consequence of intensified atmospherically driven sea ice transport and deformations (i.e., ice divergence and shear) in this area. The Davies Strait, the east coast of Greenland and the BS regions are characterized by convergence and divergence changes connected with thinner sea ice at the ice borders along with an enhanced impact of atmospheric wind forcing. Low-pressure anomalies that developed over the eastern Arctic during JFM 2020 increased northerly winds from the cold Arctic Ocean to the BS and accelerated the southward drift of the MOSAiC ice floe. The satellite-derived and simulated sea ice velocity anomalies, which compared well during JFM 2020, indicate a strong acceleration of the Transpolar Drift relative to the mean for the past decade, with intensified speeds of up to 6 km d -1. As a consequence, sea ice transport and deformations driven by atmospheric surface wind forcing accounted for the bulk of the SIT anomalies, especially in January 2020 and February 2020. RASM intra-annual ensemble forecast simulations with 30 ensemble members forced with different atmospheric boundary conditions from 1 November 2019 through 30 April 2020 show a pronounced internal variability in the sea ice volume, driven by thermodynamic ice-growth and ice-melt processes and the impact of dynamic surface winds on sea ice formation and deformation. A comparison of the respective SIT distributions and turbulent heat fluxes during the positive AO phase in JFM 2020 and the negative AO phase in JFM 2010 corroborates the conclusion that winter sea ice conditions in the Arctic Ocean can be significantly altered by AO variability. [ABSTRACT FROM AUTHOR]

Because of the harsh weather conditions on the Antarctic continent, year-round observations of the lowlevel boundary layer must be obtained via automated data acquisition systems. Alexander Tall Tower! is an automatic weather station on the Ross Ice Shelf in Antarctica and has been operational since February 2011. At 30m tall, this station has six levels of instruments to collect environmental data, including temperature, wind speed and direction, relative humidity, and pressure. Data are collected at 30-, 15-, 7.5-, 4-, 2-, and 1-m levels above the snow surface. This study identifies short-term trends and provides an improved description of the lowest portion of the boundary layer over this portion of the Ross Ice Shelf for the February 2011-January 2014 period. Observations indicate two separate initiations of the winter season occur annually, caused by synoptic-scale anomalies. Sensible and latent heat flux estimates are computed using Monin-Obukhov similarity theory and vertical profiles of potential air temperature and wind speed. Over the three years, the monthly mean sensible heat flux ranges between 1 and 39 W m-2 (toward the surface) and the monthly mean latent heat flux ranges between -8 and 0 W m-2. Net heat fluxes directed toward the surface occur most of the year, indicating an atmospheric sink of energy. [ABSTRACT FROM AUTHOR]

Abstract: Within larger ice-free regions of the western Arctic Seas, subject to ongoing trophic cascades induced by past overfishing, as well as to possible future eutrophication of the drainage basins of the Yukon and Mackenzie Rivers, prior very toxic harmful algal blooms (HABs) – first associated with ∼100 human deaths near Sitka, Alaska in 1799 – may soon expand. Blooms of calcareous coccolithophores in the Bering Sea during 1997–1998 were non-toxic harbingers of the subsequent increments of other non-siliceous phytoplankton. But, now saxitoxic dinoflagellates, e.g. Alexandrium tamarense, were instead found by us within the adjacent downstream Chukchi Sea during SBI cruises of 2002 and 2003. A previous complex, coupled biophysical model had been validated earlier by ship-board observations from the Chukchi/Beaufort Seas during the summer of 2002. With inclusion of phosphorus as another chemical state variable to modulate additional competition by recently observed nitrogen-fixers, we now explore here the possible consequences of altered composition of dominant phytoplankton functional groups [diatoms, microflagellates, prymnesiophyte Phaeocystis colonies, coccolithophores, diazotrophs, and dinoflagellates] in relation to increases of the toxic A. tamarense, responding to relaxation of grazing pressure by herbivores north of Bering Strait as part of a continuing trophic cascade. Model formulation was guided by validation observations obtained during 2002–2004 from: cruises of the SBI, CHINARE, and CASES programs; moored arrays in Bering Strait; other RUSALCA cruises around Wrangel Island; and SBI helicopter surveys of the shelf-break regions of the Arctic basin. Our year-long model scenarios during 2002–2003 indicate that post bloom silica-limitation of diatoms, after smaller simulated spring grazing losses, led to subsequent competitive advantages in summer for the coccolithophores, dinoflagellates, and diazotrophs. Immediate top-down control is exerted by imposed grazing pressures of the model’s herbivores and bottom-up control is also effected by light-, nitrate-, ammonium-, silicate-, and phosphate-modulated competition among the six functional groups of the simulated phytoplankton community. Similar to the history of the southern North Sea adjacent to the Rhine River, possible farming of northwestern Alaska and Canada, in conjunction with other human activities of ice retreat and overfishing, may lead to future exacerbations of poisonous phytoplankton. These potential killers include both toxic dinoflagellate and diazotroph HABs, deadly to terrestrial and marine mammals, as well as those of prymnesiophytes, some of which have already foamed beaches, while others have killed fishes of European waters. [Copyright &y& Elsevier]

Atmospheric rivers (ARs), intrusions of warm and moist air, can effectively drive weather extremes over the Arctic and trigger subsequent impact on sea ice and climate. What controls the observed multi-decadal Arctic AR trends remains unclear. Here, using multiple sources of observations and model experiments, we find that, contrary to the uniform positive trend in climate simulations, the observed Arctic AR frequency increases by twice as much over the Atlantic sector compared to the Pacific sector in 1981-2021. This discrepancy can be reconciled by the observed positive-to-negative phase shift of Interdecadal Pacific Oscillation (IPO) and the negative-to-positive phase shift of Atlantic Multidecadal Oscillation (AMO), which increase and reduce Arctic ARs over the Atlantic and Pacific sectors, respectively. Removing the influence of the IPO and AMO can reduce the projection uncertainties in near-future Arctic AR trends by about 24%, which is important for constraining projection of Arctic warming and the timing of an ice-free Arctic., (© 2024. Battelle Memorial Institute, Chen, Rasch, Fu, Kravitz, Cassano, Maslowski.)

Over a five-month time window between March and July 2020, scientists deployed two small uncrewed aircraft systems (sUAS) to the central Arctic Ocean as part of legs three and four of the MOSAiC expedition. These sUAS were flown to measure the thermodynamic and kinematic state of the lower atmosphere, including collecting information on temperature, pressure, humidity and winds between the surface and 1 km, as well as to document ice properties, including albedo, melt pond fraction, and open water amounts. The atmospheric state flights were primarily conducted by the DataHawk2 sUAS, which was operated primarily in a profiling manner, while the surface property flights were conducted using the HELiX sUAS, which flew grid patterns, profiles, and hover flights. In total, over 120 flights were conducted and over 48 flight hours of data were collected, sampling conditions that included temperatures as low as -35 °C and as warm as 15 °C, spanning the summer melt season., (© 2022. The Author(s).)