Vladimir F. Radionov

Snow Depth on Arctic Sea Ice

Snow depth and density were measured at Soviet drifting stations on multiyear Arctic sea ice. Measurements were made daily at fixed stakes at the weather station and once- or thrice-monthly at 10-m intervals on a line beginning about 500 m from the station buildings and extending outward an additional 500 or 1000 m. There were 31 stations, with lifetimes of 1‐7 yr. Analyses are performed here for the 37 years 1954‐91, during which time at least one station was always reporting. Snow depth at the stakes was sometimes higher than on the lines, and sometimes lower, but no systematic trend of snow depth was detected as a function of distance from the station along the 1000-m lines that would indicate an influence of the station. To determine the seasonal progression of snow depth for each year at each station, priority was given to snow lines if available; otherwise the fixed stakes were used, with an offset applied if necessary. The ice is mostly free of snow during August. Snow accumulates rapidly in September and October, moderately in November, very slowly in December and January, then moderately again from February to May. This pattern is exaggerated in the Greenland‐Ellesmere sector, which shows almost no net accumulation from November to March. The Chukchi region shows a steadier accumulation throughout the autumn, winter, and spring. The average snow depth of the multiyear ice region reaches a maximum of 34 cm (11 g cm22) in May. The deepest snow is just north of Greenland and Ellesmere Island, peaking in early June at more than 40 cm, when the snow is already melting north of Siberia and Alaska. The average snow density increases with time throughout the snow accumulation season, averaging 300 kg m23, with little geographical variation. Usually only two stations were in operation in any particular year, so there is insufficient information to obtain the geographical pattern of interannual variations. Therefore, to represent the geographical and seasonal variation of snow depth, a two-dimensional quadratic function is fitted to all data for a particular month, irrespective of year. Interannual anomalies for each month of each year are obtained relative to the long-term mean snow depth for the geographical location of the station operating in that particular year. The computed interannual variability (IAV) of snow depth in May is 6 cm, but this is larger than the true IAV because of inadequate geographical sampling. Weak negative trends of snow depth are found for all months. The largest trend is for May, the month of maximum snow depth, a decrease of 8 cm over 37 yr, apparently due to a reduction in accumulation-season snowfall.

Maritime Aerosol Network as a component of Aerosol Robotic Network

The paper presents the current status of the Maritime Aerosol Network (MAN), which has been developed as a component of the Aerosol Robotic Network (AERONET). MAN deploys Microtops handheld Sun photometers and utilizes the calibration procedure and data processing (Version 2) traceable to AERONET. A web site dedicated to the MAN activity is described. A brief historical perspective is given to aerosol optical depth (AOD) measurements over the oceans. A short summary of the existing data, collected on board ships of opportunity during the NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project is presented. Globally averaged oceanic aerosol optical depth (derived from island-based AERONET measurements) at 500 nm is similar to 0.11 and Angstrom parameter (computed within spectral range 440-870 nm) is calculated to be similar to 0.6. First results from the cruises contributing to the Maritime Aerosol Network are shown. MAN ship-based aerosol optical depth compares well to simultaneous island and near-coastal AERONET site AOD.

Aerosols in polar regions: A historical overview based on optical depth and in situ observations

Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and ...

Multiple Effects of Changes in Arctic Snow Cover

Snow cover plays a major role in the climate, hydrological and ecological systems of the Arctic and other regions through its influence on the surface energy balance (e.g. reflectivity), water balance (e.g. water storage and release), thermal regimes (e.g. insulation), vegetation and trace gas fluxes. Feedbacks to the climate system have global consequences. The livelihoods and well-being of Arctic residents and many services for the wider population depend on snow conditions so changes have important consequences. Already, changing snow conditions, particularly reduced summer soil moisture, winter thaw events and rain-on-snow conditions have negatively affected commercial forestry, reindeer herding, some wild animal populations and vegetation. Reductions in snow cover are also adversely impacting indigenous peoples’ access to traditional foods with negative impacts on human health and well-being. However, there are likely to be some benefits from a changing Arctic snow regime such as more even run-off from melting snow that favours hydropower operations.

Volcanic perturbation of the atmosphere in both polar regions: 1991–1994

Long-term measurements by sunphotometers of the spectral dependence of aerosol optical depth are reported for several sites in the Arctic and Antarctic for the period January 1991 through December 1994. In the Antarctic a pronounced increase of atmospheric turbidity was observed at the end of September 1991. The observed wavelength dependence in aerosol optical depth indicated that the increase was due to the presence of fresh and therefore small stratospheric aerosol particles associated with the eruption of Cerro Hudson in August 1991. After the breakdown of the polar vortex in mid-November 1991 we measured a second significant increase of the aerosol optical depth. At this time the 1.0-μm aerosol optical depth was approximately 0.12 or about 10 times background levels. This second incrcase is shown to be the result of the influx of Mount Pinatubo aerosols. A similar perturbation of the aerosol optical depth was observed in the Arctic with the return of sunlight in March 1992. However, the increased loading of the Arctic stratosphere by the Pinatubo aerosols was already evident at high northern latitudes in satellite measurements at the end of 1991. Stratospheric Aerosol and Gas Experiment II stratospheric 1.0-μm optical depth measurements show that meridional transport of Pinatubo aerosol from equatorial to middle and higher latitudes is greatest in the winter/spring hemisphere. This observation explains the observed seasonal trend of aerosol optical depth during the posteruption. A significant decrease of the perturbation by Mount Pinatubo aerosol was observed in both polar regions by the end of 1994. The measured 1.0-μm aerosol optical depths at this time were only 0.04 ; these values exceed the background level by about 0.01-0.02. Therefore the aerosol optical depth values are still slightly higher than during undisturbed conditions. In addition, we show that the occurrence of volcanic aerosols caused changes in the spectral dependence of the aerosol optical depth in the Arctic and the Antarctic. These variations, including the changes in the aerosol size distribution, derived from the aerosol optical depth, are discussed in comparison to undisturbed conditions.

Comparison of trends in the tropospheric and stratospheric aerosol optical depths in the Antarctic

Temporal variations of the aerosol optical depth of the Antarctic troposphere and stratosphere are considered on the basis of long-term Sun photometer and actinometer measurements which have been made at Mirny and Georg Forster stations since 1956 and 1988, respectively. This data is supplemented by measurements of the stratospheric aerosol optical depth by the satellite-borne stratospheric aerosol measurement II instrument. These observations indicate that under undisturbed conditions, the stratospheric aerosol optical depth represents approximately 25% of the total atmospheric aerosol optical depth. The aerosol optical depth in the Antarctic is most notably affected by volcanic eruptions, such as El Chichon in 1982 and Mount Pinatubo and Cerro Hudson in 1991, and by the occurrence of polar stratospheric clouds during Antarctic winter and spring. Apart from these episodic events, no long-term trend in the aerosol optical depth can be discerned from the nearly 40-year record.

Radiosonde Observations from the Former Soviet “North Pole” Series of Drifting Ice Stations, 1954–90

An historical archive of over 25 000 radiosonde observations from the former Soviet “North Pole” series of drifting ice stations has been compiled and made available to interested researchers. This archive is the only long-term set of meteorological sounding data over the Arctic Ocean. The digital archive is a result of the multiyear, collaborative efforts of a group of United States and Russian scientists and keypunch operators working under the auspices of Working Group VIII, an area of study within the United States–Russian Federation Agreement for Protection of the Environment and Natural Resources. The archive contains soundings from 21 drifting stations over the period 1954–90 and is being distributed by the National Snow and Ice Data Center in Boulder, Colorado.

Snow cover basal ice layer changes over Northern Eurasia since 1966

An analysis is made of changes in basal ice crust layer characteristics from snow cover surveys made at 958 Russian stations since 1966. The analysis revealed that substantial changes have occurred in response to two competing processes: an increase in thaws associated with strong regional warming and an increase in the duration of the basal ice layer presence on the ground, and a shortening of the snowmelt period associated with a decrease in basal ice layer event frequency and severity. The latter appears to be the more significant process over the past 40 years. Our findings support the notion that the entire spring snowmelt process has become shorter in duration and more intense when taking into account a concomitant trend toward increasing snow depths over large regions of Russia. A more intense spring melt period has important consequences for spring flood dynamics and deserves further study.

Seasonal, interannual and long-term variability of precipitation and snow depth in the region of the Barents and Kara seas

Observation data of temperature, precipitation and snow depth have been compiled and generalized climatologically for a network of 38 stations in and around the Barents and Kara seas, for the period 1951–1992. The monthly precipitation totals were corrected for measuring errors, and the correction method is described in detail. The corrected precipitation values show that the annual precipitation in the region ranges from more than 500 mm along the coast of the Kola Peninsula to less than 200 mm in parts of the north-eastern Kara Sea. The solid fraction of the annual precipitation ranges from 70 % in northern parts to 35 % in southern parts. For the period 1951–1992 the analysis indicates decreasing trends in annual values of temperature, precipitation and snow depths in the north-eastern parts of the region.

Expeditions to the Russian Arctic to Survey Black Carbon in Snow

Snow is the most reflective natural surface on Earth, with an albedo (the ratio of reflected to incident light) typically between 70% and 85%. Because the albedo of snow is so high, it can be reduced by small amounts of dark impurities. Black carbon (BC) in amounts of a few tens of parts per billion (ppb) can reduce the albedo by a few percent depending on the snow grain size [Warren and Wiscombe, 1985; Clarke and Noone, 1985]. An albedo reduction of a few percent is not detectable by eye and is below the accuracy of satellite observations. Nonetheless, such a reduction is significant for climate. For a typical incident solar flux of 240 watts per square meter at the snow surface in the Arctic during spring and summer, an albedo change of 1% modifies the absorbed energy flux by an amount comparable to current anthropogenic greenhouse gas forcing. As a result, higher levels of BC could cause the snow to melt sooner in the spring, uncovering darker underlying surfaces (tundra and sea ice) and resulting in a positive feedback on climate [Hansen and Nazarenko, 2004].