The Influence of Blowing Snow and Precipitation on Snow Depth Change across the Ross Ice Shelf and Ross Sea Regions of Antarctica

Abstract

Measuring snowfall in the polar regions is an issue met with many complications. Across the Antarctic, ground-based precipitation measurements are only available from a sparse network of manned stations or field studies. Measurements from satellites promise to fill in gaps in time and space but are still in the early stages of development and require surface measurements for proper validation. Currently, measurements of accumulation from automated reporting stations are the only available means of tracking snow depth change over a broad area of the continent. The challenge remains in determining the cause of depth change by partitioning the impacts of blowing snow and precipitation. While a methodology for separating these two factors has yet to be developed, by comparing accumulation measurements with meteorological measurements, an assessment of whether these terms were a factor in snow depth change during an event can be made. This paper describes a field study undertaken between January 2005 and October 2006 designed to identify the influences of precipitation and horizontal snow transport on surface accumulation. Seven acoustic depth gauges were deployed at automatic weather stations (AWS) across the Ross Ice Shelf and Ross Sea regions of Antarctica to measure net accumulation changes. From these measurements, episodic events were identified and were compared with data from the AWS to determine the primary cause of depth change—precipitation or horizontal snow transport. Information regarding the local impacts of these two terms, as well as climatological information regarding snow depth change across this region, is also provided.

Characteristics of immersion freezing nuclei at the South Pole station in Antarctica

“…Lawson et al (2006) reported that at the South Pole Station blowing snow is observed when the wind speed exceeds about 4 m s −1 . Knuth et al (2010) measured a threshold of between 6.6 to 7.5 m s −1 at 10 m height for blowing dry snow at the Ross Ice Shelf. The threshold for blowing wet snow was higher at 8.5 to 9.6 m s −1 .…”

Snow on the Ross Ice Shelf: comparison of reanalyses and observations from automatic weather stations

“…Figure 1 shows the climatological near-surface (850 hPa) winds on the Ross Ice Shelf (from the ERA-Interim reanalysis data), which illustrates the varying wind conditions experienced at different stations. Most of the AWS are located in katabatic outflow paths (Mary, Linda, Elaine, Ferrell, Nascent, and Byrd) and barrier wind regimes (Sabrina), and as a result these sites experience strong winds more often than the other sites (Braaten, 1997;Parish et al, 2006;Knuth et al, 2010;Nigro et al, 2011). We expect the snow accumulation at these sites may be more affected by wind redistribution than other sites such as Margaret, which is located on the eastern side of the RIS near Roosevelt Island.…”

“…5, events that are in the region above the freshly fallen snow densities could have several causes: snow accumulation being limited by wind, higher snow densities due to wind-blown snow, or reanalysis overestimating event sizes; events that fall below the range could be either due to excess accumulation due to wind or reanalysis underestimating event sizes. At sites known to exhibit significant ablation such as Ferrell, Mary, Nascent, and Sabrina (Braaten, 1997;Knuth et al, 2010;Nigro et al, 2011), where we would expect a low bias in the ADG data (i.e. ADG snow accumulation is often limited due to wind), these sites do show a significant number of events where reanalyses are much larger than ADG events (except for the NCEP events with Mary).…”

“…As wind is the primary factor affecting the magnitude of measured accumulation (both positively and negatively), previous studies can help provide some estimate of the frequency of high winds occurring during accumulation events on the RIS and their effects on measured accumulation (Braaten, 1997(Braaten, , 2000Knuth et al, 2010). Based on wind speed measurements for several stations on the RIS, Knuth et al (2010) showed that most (72 %) measured large accumulation events (> 1 cm per 30 min) were associated with blowing or drifting snow which may or may not have been concurrent with precipitation.…”

“…Based on wind speed measurements for several stations on the RIS, Knuth et al (2010) showed that most (72 %) measured large accumulation events (> 1 cm per 30 min) were associated with blowing or drifting snow which may or may not have been concurrent with precipitation. In another study on the RIS, Braaten (1997) showed that while most ADG-measured accumulation events were associated with human-observed precipitation events (using a much smaller event size threshold of 1.3 mm), less than half of the observed events (38 %) resulted in measurable accumulation by the instrument.…”