Climate Controls & Climate Change

Meso-scale and Micro-scale Climate Controls

Cleveland's climate is influenced by a number of meso-scale climate controls. The city is situated on the coast of Lake Erie, which is a significantly large body of water. Cold temperatures persist longer into spring because the lake takes longer to heat up than the land. Conversely, temperatures in autumn remain warm for longer than they otherwise would because the lake continues to retain heat.

A combination of meso-scale and micro-scale climate controls produce what is know as "lake-effect snow" during the winter. On the meso-scale, the movement of the jet stream south combined with heat retention in Lake Erie cause clouds to form as the water heats and humidifies the cold polar air that passes over it. A steep ridge on the east side of Cleveland is a unique micro-scale topographic feature that forces the clouds to rise orographically. The air is then cooled adiabatically, eventually reaches the dew point, and falls as snow.

This map shows the elevation of the Greater Cleveland area. You can see that the eastern suburbs near Cleveland Heights rise steeply from around 600 feet to over 1,000 feet above sea level. This micro-scale climate control is one reason why the east side of Cleveland receives significantly more snowfall than the west side.
Source: http://en-gb.topographic-map.com/places/Cleveland-922170/

Also on the meso-scale, the dominance of different air masses over the Cleveland area at different times of the year cause seasonal variations in temperature. During the summer, the maritime tropical air mass dominates and brings warm moist air from the Gulf of Mexico. In the wintertime, the continental polar air mass dominates and brings cold air from Siberia and Canada to Cleveland.

The urban heat island effect is an anthropogenic micro-scale climate control that also affects Cleveland. The replacement of natural vegetation with low albedo surfaces such as asphalt and concrete has decreased the overall albedo of the city, resulting in higher temperatures. Cleveland is on average 2.5° F hotter than nearby rural areas and can get up to 21°F hotter ("Hot and Getting Hotter").

The map illustrates the percentage of tree cover in Cuyahoga County. Only 11-20% of the city has tree cover, which is significantly lower than the surrounding areas. On the micro-scale, the removal of vegetation due to urbanization is one reason why Cleveland is on average 2.5°F hotter than nearby rural areas.
Source: Cuyahoga County Urban Tree Canopy Assessment
Historical Temperature Trends

Data Source: NOAA National Climatic Data Center

Data Source: NOAA National Climatic Data Center

The two graphs above display the average high and low temperatures for January and July from 1950 to 2014. Temperatures are a lot more variable from year to year in January than July. This is due to the annual variability of the polar jet stream. When the polar jet is pushed farther south by continental polar air masses, then Cleveland experiences more frigid temperatures. For instance, in 1977 the polar jet must have been much farther south than normal to produce an average low temperature of only 2.5°F! When the polar jet recedes north in the summer and the maritime tropical air mass dominates the Cleveland region, temperatures are much more stable. 

Over the long-term, average temperatures in Cleveland appear to be have been relatively stable since 1950. There is no discernible increase in the trendline for average high temperatures. However, there is a very slight increase of the average low temperatures. Since 1950, temperatures have not been getting quite as cold. This is likely due to global climate change. As the amount of greenhouse gases in the atmosphere increase, they absorb more long-wave radiation, leading to warmer temperatures.

Comparison to Seattle

According to the Koppen-Geiger climate classification system, Seattle has a sub-tropical climate with warm, dry summers, or Csb. Comparatively, Cleveland has a continental climate that is wet all year with hot summers, or Dfa. Though the Koppen-Geiger system is not perfect, it is fairly accurate in describing the climates of these two locations, as is evident in the climographs below.

On the map of Koppen-Geiger climates, you can see that Seattle is considered a Csb climate and Cleveland is a Dfa climate, based on their measured temperatures, precipitation, and natural vegetation.
Source: www.eoearth.org


The city of Seattle is located 7°N of Cleveland, but actually has a milder climate with less diurnal and seasonal temperature variation. This is because Seattle is located on the coast and has a maritime climate, while Cleveland is in the interior of the continent. Because water takes longer to heat up and cool down it acts as a moderating influence on Seattle's temperatures. 

Seattle has a much wetter winter than summer due to the subpolar low pressure system that dips down into the area, bringing moist maritime polar air with it. Cleveland on the other hand gets slightly more precipitation during the summer months due to the maritime tropical air mass that brings moisture up from the Gulf of Mexico. However, Cleveland receives abundant precipitation year round. Perhaps surprisingly, Cleveland actually receives slightly more annual precipitation than Seattle (at least as measured at their respective airports), since the winter months also bring significant precipitation in the form of lake-effect snow ("Climate Seattle - Washington", "Climate Cleveland - Ohio").


You can see that due to its coastal location Seattle has less seasonal and diurnal temperature variation compared to Cleveland, which is located in the interior of the continent. Seattle receives more precipitation in the winter due to the subpolar low pressure patterns bringing moist maritime polar air into the area.
Data Source: NOAA National Climatic Data Center

Despite Seattle's rainy reputation, Cleveland actually receives slightly more annual precipitation thanks to maritime tropical air in the summer and lake-effect snow in the winter.
Data Source: NOAA National Climatic Data Center

Both Seattle and Cleveland are affected by meso-scale convergence that leads to precipitation. Seattle has what is known as the Puget Sound Convergence Zone. The Olympic Mountains cause air masses to split and then converge over Puget Sound. This can lead to updrafts, convection, and eventually precipitation (Calvin).

Source: www.komonews.com
As discussed in previous blog entries, Cleveland is affected by lake-effect snow. As moisture-laden air crosses the lake, the friction is less over the water than it would be over land. When the air reaches the land it slows down due to the increase in friction, which causes it to converge near the shoreline. The heaviest snowfall is within this convergence zone (Haby).

With lake-effect snow, convergence occurs near the eastern shoreline of the lake, contributing to heavier snowfall.
Source: www.ess.uci.edu

 
References

Calvin, Andrew. "Geog 3232 Post 3". Calvin3232.blogspot.com. Weather and Climate. 08 May 2015. Web. 08 May 2015.

"Climate Cleveland - Ohio." Usclimatedata.com. U.S. Climate Data. N.d. Web. 08 May 2015.

"Climate Seattle - Washington.  Usclimatedata.com. U.S. Climate Data. N.d. Web. 08 May 2015.

Haby, Jeff. "LES: Fricational Convergence." Theweatherprediction.com. The Weather Prediction. N.d. Web 08 May 2015.

"Hot and Getting Hotter: Heat Island Cooking U.S. Cities." Climatecentral.org. Climate Central. 20 Aug. 2014. Web. 03 May 2015.

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