John M. Hanesiak

Meteorological forcing of sea ice concentrations in the southern Beaufort Sea over the period 1979 to 2000

[1] Northern Hemisphere sea ice areal extent, and perhaps thickness, have shown a detectable reduction over the past several decades. This situation is particularly apparent in the southern Beaufort Sea. The region encompassing the Mackenzie Shelf, the Cape Bathurst Polynya, and the Canada Basin mobile pack ice all occur in a region referred to here as the Canadian Arctic Shelf Exchange study area (CASES). In this paper we present results from an analysis of atmosphere, sea ice, and ocean coupling over the period 1979 to 2000 as a means of setting a physical science context for the CASES research network (operating over the period 2001-2005). Results show that the Cape Bathurst Polynya complex can be considered as a recurrent polynya; particularly the flaw leads associated with the early opening of the polynya. The Polynya appears to be a consequence of the Beaufort Sea Gyre acting like an ice bridge and a series of flaw leads creating conditions conducive to oceanic upwelling. The sea ice average areal extent has been decreasing in this region over the period 1979 to 2000. Large regional reductions are found (I) north of the Yukon and Alaska Coasts in the region between the Canada Basin pack ice and the landfast sea ice and (2) at the eastern limit of the Cape Bathurst Polynya in Amundsen Gulf. The meteorological forcing of sea ice anomalies occurs through a full range of timescales and space scales. At hemispheric scales a statistical cross-correlation analysis between weekly sea ice concentration anomalies and the Arctic Oscillation accounts for a maximum of about 25 percent of the explained variance and show a surprising spatial coherence in correlation magnitudes both within the study area and northward along the Canadian Archipelago coast. At local scales, positive and negative concentration anomaly periods can be explained through local-scale advective processes associated with regional-scale sea level pressure, 500 hPa geopotential heights, and surface temperature anomalies.

Sea‐ice and meteorological conditions in Northern Baffin Bay and the North Water polynya between 1979 and 1996

Abstract In this paper we provide an overview of the meteorological and sea‐ice conditions within the northern portion of Baffin Bay and the region of the North Water (NOW) Polynya between Ellesmere Island and Greenland. Our results indicate an east‐west temperature gradient across the NOW and Baffin Bay regions with colder temperatures on the Ellesmere Island coast (‐14°C) and warmer temperatures on the Greenland coast (‐9°C). This is caused by warm air advection (upper level and boundary layer) due to prevailing atmospheric flows. The sea level pressure (SLP) pattern exhibits a pronounced inverted trough in Baffin Bay extending from a quasi‐stationary low south of Greenland. The trough deepens in winter thereby tightening the pressure gradient across the NOW region. This results in maximum winds (northerly) in winter. The trough also creates a mean cyclonic gyre in Baffin Bay, mirroring the spatial pattern of annual ice concentrations. The polynya is formed between November and March as a result of the annual appearance of an ice bridge in Smith Sound along with a northerly surface flow. The formation and duration of the ice bridge is shown to be highly variable and appears to be forming later and breaking earlier in the 1990s compared with the 1980s. The average sea‐ice formation and decay dates closely follow the mean temperature spatial pattern, illustrating a strong atmosphere‐surface coupling. Results show that the NOW region has several distinct sea‐ice anomaly patterns. These patterns consist of areas of high anomalous concentrations of sea ice which are consistent spatially and temporally. A ‘bridge dipole’ operates out of phase (e.g., as ice anomalies increase (decrease) in Nares Strait they decrease (increase) in Smith Sound). A ‘gyre dipole’ operates in phase between Smith Sound and the south‐west coast of Greenland. When concentration anomalies are negative (positive) in Smith Sound they are also negative (positive) along the south‐west coast of Greenland. We speculate that these links may be useful indicators of the response of the NOW region to climate variability and change.

The Mesoscale and Microscale Structure of a Severe Ice Pellet Storm

Abstract On 1–2 February 1992 a major storm produced a prolonged period (6 h) of ice pellets over St. Johns, Newfoundland. At least two key features contributed to the prolonged duration. First, a subsaturated region within an inversion led to a reduction in the melting rate of particles that eventually meant that they could completely refreeze in the lower subfreezing region. This subsaturated region formed within descending air aloft identified by Doppler radar observations. Second, a cold core of air between the surface and the inversion was critically important for the refreezing of partially melted particles. Results from an airmass transformation model were used to show that the ice pellet duration was extended as a result of air traveling over sea ice as opposed to over the ocean. In addition, this study showed that Doppler radar velocity information may be capable of estimating the base height of the above freezing temperature regime during freezing rain/drizzle. Furthermore, the Doppler velocity...

The 2015 Plains Elevated Convection at Night Field Project

AbstractThe central Great Plains region in North America has a nocturnal maximum in warm-season precipitation. Much of this precipitation comes from organized mesoscale convective systems (MCSs). This nocturnal maximum is counterintuitive in the sense that convective activity over the Great Plains is out of phase with the local generation of CAPE by solar heating of the surface. The lower troposphere in this nocturnal environment is typically characterized by a low-level jet (LLJ) just above a stable boundary layer (SBL), and convective available potential energy (CAPE) values that peak above the SBL, resulting in convection that may be elevated, with source air decoupled from the surface. Nocturnal MCS-induced cold pools often trigger undular bores and solitary waves within the SBL. A full understanding of the nocturnal precipitation maximum remains elusive, although it appears that bore-induced lifting and the LLJ may be instrumental to convection initiation and the maintenance of MCSs at night.To gain ...

Role of diurnal processes in the seasonal evolution of sea ice and its snow cover

Comparisons between hourly forced data simulations and daily average forced simulations using a one-dimensional thermodynamic sea ice model show that diurnal changes in the surface energy balance that directly affect the snow depth, albedo, and surface temperature ultimately affect modeled seasonal ice evolution. Hourly forcing produces earlier onset of snowmelt, and open water duration is increased by 21 days. These differences are due to nonlinearities associated with absorbed shortwave radiation as well as latent and sensible heat fluxes. The accuracy of model parameterizations of downwelling shortwave (K↓) and longwave (L↓) fluxes and albedo over diurnal timescales is assessed by comparison to field observations made during the Seasonal Ice Monitoring and Modeling Site (SIMMS) 1992–1993 field experiments near Resolute Bay, Northwest Territories. Mean K↓ errors (modeled - observed) were −23 W m−2, with a standard deviation of 89 W m−2, and mean L↓, errors were −1 W m−2, with a standard deviation of 18.8 W m−2. Modeled dry/new snow and wet snow albedos were about 0.1 and 0.05, respectively, lower than those observed, allowing greater amounts of shortwave energy absorption into the snowpack. Using SIMMS 1992 on-ice field data as replacement for model K↓, L↓, and albedo parameterizations shows very different spring period simulations compared with using hourly forcing from Resolute land-based observations. Simulated net surface flux, surface temperature, and snow-ice ablation were significantly improved.

The Structure, Water Budget, and Radiational Features of a High-Latitude Warm Front

Abstract On 30 September 1994 an Arctic low pressure system passed over the southern Beaufort Sea area of northern Canada and research aircraft observations were made within and around the warm front of the storm. This study is unique in that the warm front contained subzero centigrade temperatures across the entire frontal region. The overall structure of the warm front and surrounding region was similar to midlatitude storms; however, the precipitation rates, liquid water content magnitudes, horizontal and vertical winds, vertical wind shear, turbulence, and thermal advection were very weak. In addition, a low-level jet and cloud bands were aligned parallel to the warm front, near-neutral stability occurred within and around the front, and conditional symmetric instability was likely occurring. A steep frontal region resulted from strong Coriolis influences that in turn limited the amount of cloud and precipitation ahead of the system. The precipitation efficiency of the storm was high (60%) but is beli...

STORM STUDIES IN THE ARCTIC (STAR)

The Storm Studies in the Arctic (STAR) network (2007–2010) conducted a major meteorological field project from 10 October–30 November 2007 and in February 2008, focused on southern Baffin Island, Nunavut, Canada—a region that experiences intense autumn and winter storms. The STAR research program is concerned with the documentation, better understanding, and improved prediction of meteorological and related hazards in the Arctic, including their modification by local topography and land–sea ice–ocean transitions, and their effect on local communities. To optimize the applicability of STAR network science, we are also communicating with the user community (northern communities and government sectors). STAR has obtained a variety of surface-based and unique research aircraft field measurements, high-resolution modeling products, and remote sensing measurements (including Cloudsat) as part of its science strategy and has the first arctic Cloudsat validation dataset. In total, 14 research flights were flown b...

Measurements of drifting and blowing snow at Iqaluit, Nunavut, Canada during the STAR Project.

Abstract A 10 m meteorological tower near Iqaluit Airport was operational from late October 2007 to early April 2008. Measurements included wind speed, temperature, pressure, humidity, visibility, and blowing snow number flux. Number flux measurements give a frequency of blowing and drifting snow of approximately 10% for the duration of the study, while meteorological observations from the Iqaluit weather office give a frequency of approximately 5%. Winter winds were predominantly from the northwest, and some strong southeasterly winds were also observed, especially in early spring. The average roughness length determined from the variance of wind speed is z0 = 0.14 mm. Threshold wind speeds for the onset of blowing snow ranged from 7 m s–1 to 12 m s–1, excluding events with falling snow. Measurements of visibility correlate well with the measured number density (R2 = 0.83), assuming a constant particle diameter of d ≈ 100 μm at a height of 2 m. A camera system was used during blowing snow events in February to measure the size of blowing snow particles and the mass flux of blowing snow. At a height of 0.35 m, the particle size distribution can be approximated by a gamma distribution with shape parameter 4.4 < α < 6.4 and an average particle diameter of 70 < d < 148 μm. The particle size at a height of 0.35 m increases linearly with the 10 m wind speed (R2 = 0.69). Mass flux measurements demonstrate a power law relation with height between 0.1 and 0.9 m, with a negative exponent of approximately 2.5. Blowing snow density follows a power law relation with height between 0.85 and 1.85 m, with a negative exponent of approximately 1.3 for friction velocity 0.25 < u* < 0.55 m s–1. In February 2008, a field mill was installed, which measured electric field strengths as high as 26.2 kV m–1 at a height of 0.5 m.

Visibility during Blowing Snow Events over Arctic Sea Ice

Abstract A field study on visibility during Arctic blowing snow events over sea ice in Franklin Bay, Northwest Territories, Canada, was carried out from mid-January to early April 2004 during the Canadian Arctic Shelf Exchange Study (CASES) 2003–04 expedition. Visibilities at two heights, wind and temperature profiles, plus blowing and drifting snow particle flux at several heights were monitored continually during the study period. Good relations between visibility and wind speed were found in individual events of ground blowing snow with coefficients of determination >0.9. Regression equations relating 1.5-m height visibility to 10-m wind speed can be used for predicting visibility with a mean relative error in the range of 19%–32%. Similar regression functions obtained from the data for observed visibility of less than 1 km could predict visibilities more accurately for more extreme visibility reductions and wind speeds (>9.5 m s−1) with mean relative error ranging from 15% to 26%. For the event of gro...

Parametrization schemes of incident radiation in the North Water polynya

Abstract Surface incident radiation is a critical component of the Arctic surface energy balance making it important for sea‐ice model parametrizations to properly account for these fluxes. In this article, we test the performance of various incident short‐wave (K?) and long‐wave (L?) flux parametrizations using unique observations from the 1998 International North Water (NOW) Polynya Project between March and July. The dataset includes hourly observations over terrestrial, fast‐ice and full marine polynya environments allowing for parametrization comparisons between each environment and determination of any seasonal biases. Performance testing is highly dependent on observed input parameters that contain relative errors, however, significant differences between the marine and fast‐ice fluxes are evident. Results are very similar between the terrestrial and fast‐ice sites. The best K? clear‐sky schemes underestimate fluxes in the colder season and overestimate them in the warm season, with greater biases in the marine setting. The K? cloudy‐sky results suggest a similar cold and warm season bias but with greater magnitudes, especially in the marine environment. The K? cloudy‐sky schemes require seasonal improvements, especially in the marine atmosphere. The L? clear‐sky fluxes were generally overestimated during the colder season. Accounting for a less emissive atmosphere resulted in better flux approximations in all environments. L? cloudy‐sky fluxes were generally underestimated. Adjusting the cloudy‐sky emissivity improved the estimated fluxes, however, results were very different in the marine setting. The L? cloudy‐sky parametrizations may require re‐evaluation due to a consistent negative bias as the observed flux increases.