• Applicability of synthetic aperture radar for investigating river breakup on the Kuparuk River, Northern Alaska

      Floyd, Angelica L. (2012-12)
      A combined use of remote sensing techniques and field measurements is a pragmatic approach to study Arctic hydrology, given the vastness, complexity, and logistical challenges posed by most Arctic watersheds. This study investigates the use of synthetic aperture radar (SAR) to define spring breakup of the Kuparuk River on the North Slope of Alaska. A time series (years 2001-2010) of SAR images was assembled at the river mouth on the Arctic Coastal Plain. A statistical analysis was used and was limited to three variables: image brightness, variance in brightness over the river length, and a rank order analysis accomplished by segmenting the river and ranking segments in order of relative brightness. Variance was the only reliable breakup indicator of the three tested. A shorter one year temporal stack was assembled at the river's headwaters for a visual interpretation, which had limited success. Results from both analyses were calibrated with in-situ stream gauge data. River ice breakup is a highly complex process which may be defined differently by the remote sensing community and hydrologists, due to the sensitive nature of SAR, which may indicate surficial changes on the river before any discharge is recorded.
    • Impact of Daily Arctic Sea Ice Variability in CAM3.0 during Fall and Winter

      Dammann, Dyre O.; Bhatt, Uma S.; Langen, Peter L.; Krieger, Jeremy R.; Zhang, Xiangdong (2013-03-15)
      Climate projections suggest that an ice-free summer Arctic Ocean is possible within several decades and with this comes the prospect of increased ship traffic and safety concerns. The daily sea ice concentration tendency in five Coupled Model Intercomparison Project phase 5 (CMIP5) simulations is compared with observations to reveal that many models underestimate this quantity that describes high-frequency ice movements, particularly in the marginal ice zone. To investigate whether high-frequency ice variability impacts the atmosphere, the Community Atmosphere Model, version 3.0 (CAM3.0), is forced by sea ice with and without daily fluctuations. Two 100-member ensemble experiments with daily varying (DAILY) and smoothly varying (SMTH) sea ice are conducted, along with a climatological control, for an anoma- lously low ice period (August 2006–November 2007). Results are presented for three periods: September 2006, October 2006, and December–February (DJF) 2006/07. The atmospheric response differs between DAILY and SMTH. In September, sea ice differences lead to an anomalous high and weaker storm activity over northern Europe. During October, the ice expands equatorward faster in DAILY than SMTH in the Siberian seas and leads to a local response of near-surface cooling. In DJF, there is a 1.5-hPa positive sea level pressure anomaly over North America, leading to anomalous northerly flow and anomalously cool continental U.S. temperatures. While the atmospheric responses are modest, the differences arising from high temporal frequency ice variability cannot be ignored. Increasing the accuracy of coupled model sea ice variations on short time scales is needed to improve short-term coupled model forecasts.
    • Role of Arctic Sea Ice Variability in Climate Models

      Dammann, Dyre O.; Bhatt, Uma; Polyakov, Igor; Zhang, Xiang (2011-08)
      Arctic sea ice plays an important role in climate by influencing surface heat fluxes and albedo, so must be accurately represented in climate models. This study finds that the fully coupled ice-ocean-atmosphere-land Community Climate System Model (CCSM3.0) underestimates day-to-day ice variability compared to observations and employs the Community Atmosphere Model (CAM3.0) to investigate the atmospheric sensitivity to sea ice variability. Three 100-ensemble experiments are forced with climatological, daily-varying, and smoothly-varying sea ice conditions from an anomalously low ice period (September 2006-February 2007). Daily ice variability has a large local impact on the atmosphere when ice undergoes rapid changes, leading to local cooling and subsequent circulation changes. The most notable example of a large-scale atmospheric response occurs over Northern Europe during fall where daily ice variability forces reductions in the number and strength of cyclones, leading to positive sea level pressure anomalies, surface warming, and reduced cloud cover.