The Air-Conditioned City (Blog 1)

Blog1: Duluth, MN 

Geographically speaking, Duluth's location (Lat/Long: 46.787, -92.098) falls but a few hundred miles from the center of North America.  This would lead one to suspect a fully continental climate, however, Duluth's proximity to Lake Superior, the largest and coldest Great Lake, brings a marine influence to the climate of this small city founded at the natural harbor on the furthest southwest extent of lake. 

Ice fog, likely caused by cold land-based winds moving over the warmer open water,
seen over Lake Superior with Duluth Harbor in the foreground.

While the city is centered on the lower areas near the harbor, the city has grown onto the hills directly to the west that rise 600-800 feet above the lake.  The surrounding region is characterized by humid, deciduous forest pockmarked with innumerous lakes which canvas the glacially-scarred landscape.

Orographic influence in Duluth. Seasonal snowfall totals on Duluth's western

ridge may receive 20" or more than portions of the city at lake level.

Winter in Duluth is often bitterly cold; January has a mean daily minimum of -1.4°F.  Heavy snowfall is also commonplace  as Duluth receives an annual average of 83.1".  In all but the winter months, a northeasterly wind prevails off the lake and is somewhat trapped by the western hills.  When the warmed air rises in the evening, cooler lake air moves inland and brings milder temperatures through adiabatic cooling.  With mean daily July maximum of 76°F, one can see why Duluth is often called "the air-conditioned city." 

Average monthy precipitation and temperature ranges covey the harsh winters and mild summers in Duluth.  Yearly mean daily maximum temperatures for the year is 48°F; records show daily minumums have been as low as -39°F and daily maximums have not exceeded 97°F.  December, January and February receive significantly less precipitation than other months, however, snowfalls of over 30" have been recorded during this drier period.

Duluth, MN temperature data, 1971-2000.

 Although, open water influences heat fluxes in Duluth, the sensible heat flux plays a large role due to the continentality of the region.  In general, this value is expected to fall below the average ratio of North America (0.74); an estimated Bowen Ratio is 0.5, which postulates that about twice as much energy exchange is involved in the latent heat flux than in the sensible heat flux.

GIS map showing disproportionate annual snowfall is comparison with areas to the south and west.
Because of the variation of local climate from that of the surrounding area, Duluth is considered a "microclimate".

GeeBIT

A) 0.406 Albedo = 4.0°C

     0.206 Albedo = 24.8°C

B) G.H. Factor of 1.1 = 17.7°C

     G.H. Factor of 0.9 = 12.1°C

C) An increase to the albedo or decrease in the greenhouse factor would cause even cooler temperatures, and the harbor would likely remain frozen longer, affecting commerce.  Conversely, decreasing albedo and increasing the greenhouse effect would bridle the areas adiabatic cooling and bring more continental summer temperatures.

References:

Climate for Duluth, MN. (n.d.). Retrieved from http://www.rssweather.com/climate/Minnesota/Duluth/

Duluth, MN: Storm Tracks. (n.d.). Retrieved from http://snincr.net/winter_profiles/DuluthMN.html

Duluth (Orographic City) Local Influences. (2010, January 4). Retrieved from http://snincr.net/duluth_local_effects/duluth_local_effects.php

Normals, means, and extremes: Duluth, mn . (n.d.). Retrieved from http://climate.umn.edu/pdf/normals_means_and_extremes/2005_Annual_LCD_DLH_page_3.pdf

NWS Duluth Winter Climate Stats & Records. (n.d.). Retrieved from http://www.crh.noaa.gov/dlh/?n=duluthwinterclimate

O'Hara, D. (Photographer). (n.d.). Cold Glow. [Web Photo]. Retrieved from http://www.northernimages.com/Duluth/Weather/Duluth-Weather/7756706_sZM4q2/501596988_S5jNb

Richardson, H. W. The Climate of Duluth. (pp. 17-29). Duluth: Commercial Club of Duluth. 

           Retrieved from http://www.archive.org/stream/climateofduluthm00richrich#page/n3/mode/2up.