Shelley L. Knuth

A Dynamical Investigation of the May 2004 McMurdo Antarctica Severe Wind Event Using AMPS

On 15–16 May 2004 a severe windstorm struck McMurdo, Antarctica. The Antarctic Mesoscale Prediction System (AMPS) is used, along with available observations, to analyze the storm. A synoptic-scale cyclone weakens as it propagates across the Ross Ice Shelf toward McMurdo. Flow associated with the cyclone initiates a barrier jet along the Transantarctic Mountains. Forcing terms from the horizontal equations of motion are computed in the barrier wind to show that the local time tendency and momentum advection terms are key components of the force balance. The barrier jet interacts with a preexisting near-surface radiation inversion over the Ross Ice Shelf to set up conditions favorable for the development of large-amplitude mountain waves, leading to a downslope windstorm in the Ross Island area. Hydraulic theory can explain the structure of the downslope windstorms, with amplification of the mountain waves possibly caused by wave-breaking events. The underestimation of AMPS wind speed at McMurdo is caused by the misplacement of a hydraulic jump downstream of the downslope windstorms. The dynamics associated with the cyclone, barrier jet, and downslope windstorms are analyzed to determine the role of each in development of the severe winds.

Observations of Antarctic Polynya With Unmanned Aircraft Systems

Working in the polar environment is always challenging, particularly during the winter, when environmental conditions are harshest. With hurricane force winds, frigid temperatures, and the potential to alter the global thermohaline circulation, the Terra Nova Bay region of Antarctica in the western Ross Sea is an environment where acquiring observations of local atmospheric and oceanic interactions is critical and also extremely challenging. An important feature of Terra Nova Bay is a recurring polynya—an area of nearly ice-free water surrounded by sea ice and land. Strong katabatic winds (cold, negatively buoyant air that flows downslope under the influence of gravity) drain from the interior of the continent and blow over the open water of the polynya, resulting in large upward fluxes of heat and moisture. Sea ice production occurs as a result of the large transfer of heat from sea to air, with the newly formed sea ice blown offshore, effectively removing freshwater from the coastal ocean. The high-salinity water created through this process becomes part of the global thermohaline circulation as Antarctic bottom water. Coastal polynyas, such as the one in Terra Nova Bay, are of interest to atmospheric scientists and oceanographers due to the intense air-sea coupling and the impact of these fluxes on the state of the atmosphere and ocean.

Estimating Sensible and Latent Heat Fluxes Using the Integral Method from in situ Aircraft Measurements

AbstractIn September 2009, several Aerosonde unmanned aerial vehicles (UAVs) were flown from McMurdo Station to Terra Nova Bay, Antarctica, with the purpose of collecting three-dimensional measurements of the atmospheric boundary layer (ABL) overlying a polynya. Temperature, pressure, wind speed, and relative humidity measurements collected by the UAVs were used to calculate sensible and latent heat fluxes (SHF and LHF, respectively) during three flights. Fluxes were calculated over the depth of the ABL using the integral method, in which only measurements of the mean atmospheric state (no transfer coefficients) were used. The initial flux estimates assumed that the observations were Lagrangian. Subsequent fluxes were estimated using a robust and innovative methodology that included modifications to incorporate adiabatic and non-Lagrangian processes as well as the heat content below flight level. The SHF ranged from 12 to 485 W m−2, while the LHF ranged from 56 to 152 W m−2. The importance of properly mea...

Evaluation of Antarctic Mesoscale Prediction System (AMPS) cyclone forecasts using infrared satellite imagery

Abstract The Antarctic coast is an area of high cyclonic activity. Specifically, the regions of Terra Nova Bay, in the western Ross Sea, and Byrd Glacier, in the western Ross Ice Shelf, are prone to cyclone development. The United States, New Zealand, and Italian Antarctic programmes conduct extensive research activities in the region of the western Ross Sea. Due to the harsh weather conditions associated with the cyclonic systems that occur in this region and the abundant research activities in the area, it is important to be able to accurately predict the timing, location and strength of cyclones in this sector of Antarctica. This study evaluates the ability of the Antarctic Mesoscale Prediction System (from 2006–09) to accurately forecast cyclones in the region of the western Ross Sea by comparing the Antarctic Mesoscale Prediction System forecasts to cyclones identified in infrared satellite imagery. The results indicate that the Antarctic Mesoscale Prediction System is able to accurately predict the presence of cyclones about 40% of the time (at a minimum) and the presence of no cyclones about 70% of the time.

An Analysis of Near-Surface Winds, Air Temperature, and Cyclone Activity in Terra Nova Bay, Antarctica, from 1993 to 2009

Abstract In September 2009, the first unmanned aerial vehicles were flown over Terra Nova Bay, Antarctica, to collect information regarding air–sea interactions. Prior to the field season, wind and temperature data from a local automatic weather station (AWS) were collected from 1993 to 2007 and compared with an August–October 2006–08 satellite cyclone analysis to place the September 2009 observations into a broader context. AWS wind data revealed a strong tendency toward downslope flow in the region regardless of season, as the majority (55%) of winds were from the west to northwesterly directions. Most winds observed at the site were less than 20 m s−1, but 83% of the stronger winds were associated with downslope flow. Of 15 strong wind events (greater than 20 m s−1 for more than 10 h) evaluated during the cyclone analysis period, 100% occurred in the presence of a cyclone in the adjacent Ross Sea. Winter experienced the greatest number of strong wind events (68%), and summer had the least (4%). Most te...

The Impacts of Outreach Efforts by Research Computing at the University of Colorado Boulder

An evaluation1 of services offered by Research Computing at the University of Colorado Boulder is presented. This evaluation is attempting to determine the impact of existing services, as well as of new services introduced based on user feedback and research on equivalent HPC groups at other institutions. The available user feedback suggests that most of these services have been well-received.