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Featured researches published by Kurt Chowanski.


Journal of Climate | 2005

A Comparison of SNOTEL and GHCN/CRU Surface Temperatures with Free-Air Temperatures at High Elevations in the Western United States: Data Compatibility and Trends

Nick Pepin; Mark Losleben; M. Hartman; Kurt Chowanski

Abstract This paper compares high-elevation surface temperatures based on the Global Historical Climate Network/Climatic Research Unit (GHCN/CRU) and snow telemetry (SNOTEL) datasets, with simultaneous free-air equivalent temperatures, interpolated from NCEP–NCAR reanalysis. Mean monthly temperature anomalies from 1982 to 1999 are examined for 60 SNOTEL and 296 GHCN/CRU sites at elevations over 500 m with relatively homogenous records. The surface/free-air temperature difference ΔT (Ts − Ta) is calculated for both the SNOTEL and GHCN/CRU datasets. Topography influences the correlation between surface and free-air temperature anomalies. Physically realistic diurnal and seasonal changes in ΔT\E are illustrated. Systematic secular trends in surface temperatures, free-air temperatures, and ΔT are revealed, but the sign and magnitude of change depends on location, meaning that regional signals are weak. The Ts trends are positive for most GHCN and CRU sites, and for SNOTEL sites at night. Daytime cooling in th...


Plant Ecology & Diversity | 2015

Contrasting long-term alpine and subalpine precipitation trends in a mid-latitude North American mountain system, Colorado Front Range, USA

Timothy G. F. Kittel; Mark W. Williams; Kurt Chowanski; Michael Hartman; Todd Ackerman; Mark Losleben; Peter D. Blanken

Background: Long-term climate trends in mountain systems often vary strongly with elevation. Aims: To evaluate elevation dependence in long-term precipitation trends in subalpine forest and alpine tundra zones of a mid-continental, mid-latitude North American mountain system and to relate such dependence to atmospheric circulation patterns. Methods: We contrasted 59-year (1952–2010) precipitation records of two high-elevation climate stations on Niwot Ridge, Colorado Front Range, Rocky Mountains, USA. The sites, one in forest (3022 m a.s.l.) and the other in alpine tundra (3739 m), are closely located (within 7 km horizontally, ca. 700 m vertically), but differ with respect to proximity to the mountain-system crest (the Continental Divide). Results: The sites exhibited significant differences in annual and seasonal precipitation trends, which depended strongly on their elevation and distance from the Continental Divide. Annual precipitation increased by 60 mm (+6%) per decade at the alpine site, with no significant change at the subalpine site. Seasonally, trends at the alpine site were dominated by increases in winter, which we suggest resulted from an increase in orographically generated precipitation over the Divide, driven by upper-air (700 hPa) north-westerly flow. Such a change was not evident at the subalpine site, which is less affected by orographic precipitation on north-westerly flow. Conclusions: Elevation dependence in precipitation trends appears to have arisen from a change in upper-air flow from predominantly south-westerly to north-westerly. Dependence of precipitation trends on topographic position and season has complex implications for the ecology and hydrology of Niwot Ridge and adjacent watersheds, involving interactions among physical processes (e.g. snowpack dynamics) and biotic responses (e.g. in phenologies and ecosystem productivity).


Biogeochemistry | 2009

Process-level controls on CO2 fluxes from a seasonally snow-covered subalpine meadow soil, Niwot Ridge, Colorado

Daniel Liptzin; Mark W. Williams; Detlev Helmig; Brian Seok; Gianluca Filippa; Kurt Chowanski; Jacques Hueber


Biogeochemistry | 2009

An automated system for continuous measurements of trace gas fluxes through snow: an evaluation of the gas diffusion method at a subalpine forest site, Niwot Ridge, Colorado

Brian Seok; Detlev Helmig; Mark W. Williams; Daniel Liptzin; Kurt Chowanski; Jacques Hueber


Biogeochemistry | 2009

Storage and release of solutes from a subalpine seasonal snowpack: soil and stream water response, Niwot Ridge, Colorado

Mark W. Williams; Christine Seibold; Kurt Chowanski


Biogeochemistry | 2009

A comparison of water and carbon dioxide exchange at a windy alpine tundra and subalpine forest site near Niwot Ridge, Colorado

Peter D. Blanken; Mark W. Williams; Sean P. Burns; Russell K. Monson; John F. Knowles; Kurt Chowanski; Todd Ackerman


Biogeochemistry | 2009

Winter and summer nitrous oxide and nitrogen oxides fluxes from a seasonally snow-covered subalpine meadow at Niwot Ridge, Colorado

Gianluca Filippa; Michele Freppaz; Mark W. Williams; Detlev Helmig; Daniel Liptzin; Brian Seok; Brad Hall; Kurt Chowanski


Archive | 2009

Storage and release of solutes from a subalpine seasonal snowpack: soil and stream water response,

Mark W. Williams; Christine Seibold; Kurt Chowanski


Agricultural and Forest Meteorology | 2012

Energy and surface moisture seasonally limit evaporation and sublimation from snow-free alpine tundra

John F. Knowles; Peter D. Blanken; Mark W. Williams; Kurt Chowanski


Atmospheric Environment | 2013

Quantifying particulate matter deposition in Niwot Ridge, Colorado: Collection of dry deposition using marble inserts and particle imaging using the FlowCAM

Natasha R. Goss; Natalie Mladenov; Christine Seibold; Kurt Chowanski; Leslie Seitz; T. Barret Wellemeyer; Mark W. Williams

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Peter D. Blanken

University of Colorado Boulder

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Brian Seok

University of Colorado Boulder

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Daniel Liptzin

University of Colorado Boulder

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Christine Seibold

University of Colorado Boulder

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Todd Ackerman

University of Colorado Boulder

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Brad Hall

National Oceanic and Atmospheric Administration

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J. Hueber

University of Colorado Boulder

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Sean P. Burns

National Center for Atmospheric Research

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