HR: 0800h
AN: C21A-1083    [Abstracts]
TI: Relationships Between Atmospheric Circulation, Mountain Snowpack and Adjacent Lowland Precipitation in the Western U.S.
AU: * Pepin, N C
EM: nicholas.pepin@port.ac.uk
AF: University of Portsmouth, Department of Geography, Buckingham Building, Lion Terrace, Portsmouth, PO1 3HE United Kingdom
AU: Losleben, M
EM: Mark.Losleben@colorado.edu
AF: University of Colorado, Mountain Research Station, 818 County Rd 116, Nederland, CO 80466 United States
AU: Duane, W J
EM: bill.duane@port.ac.uk
AF: University of Portsmouth, Department of Geography, Buckingham Building, Lion Terrace, Portsmouth, PO1 3HE United Kingdom
AB: Mountain snowpack in the arid Western United States is critically important, both as a water resource and for winter recreation. This research examines high elevation snowpack in localised regions within three mountain ranges of the western United States; the Rockies, Cascades, and the Sierra Nevada. Trends in snowpack (1937-2000) as measured by Apr 1 SWE (Snow Water Equivalent) are not correlated with simultaneous trends in adjacent lowland winter (Oct-Mar) precipitation (LWP). This decoupled relationship suggests that LWP should not be used as a proxy for upland snowpack conditions, and that different influences are dominant. Snowpack is just as much influenced by ablation (controlled by temperature, wind and radiation balance) as it is by deposition (precipitation amounts), although the relative importance of these factors depends on the mountain range. To examine the contrasts between SWE and LWP response in more detail, the sensitivity of snowpack and adjacent lowland precipitation to synoptic conditions at all three sites is assessed. Interannual variability in Apr 1 SWE is greatest in the Cascades and least in the Rockies, a result of increased sensitivity to synoptic changes in the former mountain range. LWP shows contrasting patterns, being more variable in the Sierra Nevada and much less so in the Cascades. Analysis of composite 700 mb signatures (derived from NCEP/NCAR reanalysis) for years of high extreme SWE/LWP minus years of low extreme SWE/LWP also show contrasts between SWE and LWP behaviour. High and low snowpack occurrences are associated with strong anomalous circulation in the Cascades and Sierra, but not in the Rockies. Between mountain range contrasts in these synoptic signatures are less distinct for LWP. Thus our analyses suggest both that a) The snowpack in the Cascades may be the most sensitive to future climate change, while that in the Rockies the least; and b) snowpack in the three mountain ranges could respond in very different ways to future synoptic forcing, even if changes in lowland winter precipitation are more similar.
DE: 0736 Snow (1827, 1863)
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
DE: 3319 General circulation (1223)
DE: 3322 Land/atmosphere interactions (1218, 1631, 1843)
SC: Cryosphere [C]
MN: Fall Meeting 2005