Sunday, 11 January 2009
An Overview of the Marine Climate of Lincoln Rock, Alaska
Phoenix Convention Center
The maritime climate of Southeast Alaska is a volatile environment that posses considerable danger to the mariners navigating the area. Observations from lighthouses throughout the inner channels of this region are key to properly preparing for such a passage, and Lincoln Rock Lighthouse is one such example. Located in northern Clarence Strait, this former lighthouse and current automated observation site has provided weather and sea observations intermittently since the 1940's. Human observations of temperature, wind speed, wind direction, and wind gusts, along with sea and swell conditions, were recorded daily through 1968, when the light station was closed. In 2007, an automated observation system was installed, providing real-time weather conditions. Using this available data, a detailed examination of the marine climate near Lincoln Rock was made available. Wind speed and direction frequency roses are compiled, along with wind gust and direction frequency roses. In addition, temperature variance over wind direction is examined. Finally, wind conditions are compared to combined seas, comparing the interactions that lead to high seas. A bi-directional wind field (Northwesterly and Southeasterly) is clearly evident, and wind speeds increased as they shifted from southeasterly to southerly, a relationship seen in both the human and automated observations. The strongest wind speeds and gusts had a southeasterly component, matching expectations given the Northwest/Southeast orientation of the channel and climatological storm tracks. Temperature analysis showed northeasterly winds leading to temperatures more than one standard deviation below the mean, suggestive of the influences of arctic fronts during the spring, fall, and winter. Comparing combined seas to wind speeds, a direct linear relationship is established with slopes of 0.09 ft/kt. R-squared correlations for these linear lines of best fit ranged from 0.48-0.58 (seasonal dependent), with the fall and winter correlation stronger than the spring and summer. Combined seas were used to account for changes in observational techniques, allowing all wind-driven seas to be accounted for. Using the historical data set, comparisons were made to the 2007/08 data regarding wind observations. All major relations held true, though the 2007/08 observations appear shifted 22.5˚ beyond the historical data (i.e. south-southeasterly winds in the historical data appeared southerly in the 2007/08 data). This trend is likely attested to the geological magnetic shift in the area. Further analysis is limited by the small size of the 2007/08 data set, although many of the relationships established are expected to hold true in further analysis. Overall, the assessment of this historical data provides insight into the climate of Lincoln Rock as well as a cross check for current and future observations. Trends investigated in this study provide a strong basis for users of this data in the region, allowing them to make proper decisions regarding the safety of passage through these areas. Finally, the analysis techniques established here can easily be applied to other inner channel waterways in Southeast Alaska and elsewhere for further study.