Turkey Lakes watershed study site: meteorology

Meteorology (precipitation quantity, air temperature, relative humidity, wind speed and direction, barometric pressure) and atmospheric deposition are measured at the "CAPMoN" (Canadian Air and Precipitation Monitoring Network) site just outside of the basin boundary (Figure 1).

Precipitation quantity and snowpack water equivalent and chemistry are also monitored at several locations within the basin to quantify spatial variability. In addition, solar and ultra-violet radiation are measured at the CAPMoN site. National Water Research Institute (NWRI) and Meteorological Service of Canada (MSC) share responsibility for collecting this information (see Database Information for details).

An overall relief of 290 m and leeward position relative to Lake Superior influences the quantity of precipitation received by the Turkey LakesWatershed (TLW). As shown in Figure 2, annual total precipitation has ranged from 892 mm in 1997 to 1542 mm in 1988 (mean = 1215 mm).  In comparison, Sault Ste. Marie, which lies south of the highlands containing the TLW, receives only 935 mm precipitation per year (long-term average). Rain has constituted 53 to 78% of the annual precipitation (mean = 65%). Extreme precipitation events over a 24-hour period are predominantly rain episodes. From 1980 to 2006, 23 days had rainfall quantities exceeding 50 mm whereas the greatest daily snowfall was 49 mm water equivalent.

From 1980 to 2006, the mean annual , maximum and minimum air temperature in the TLWwas 4.5^oC, 6.9^oC and 2.7^oC, respectively. The annual mean daily air temperature has been increasing since 1980 at a rate of 0.118 C^oyr^-1 (slope of the linear regression line in Figure 2).  On a monthly basis, the average mean daily air temperature is highest in July (17.7^oC) and lowest in January (-11.1^oC). June and September are the third and fourth warmest months on average, but it is increases in the air temperature for these months that is principally responsible for the rise in annual temperatures.

Wind direction and speed are extremely variable.  The 1980-2001 wind direction record shows that northerly and westerly air flows are most common and easterly winds are least common.  However, there are marked seasonal differences, i.e. northerly winds predominate in autumn and winter; easterly winds are relatively more important in spring; and westerly winds predominate in summer (Figure 3).

Mean daily wind speeds are in the range 1-2 m sec^-1with some seasonal variation (Figure 4).  On a seasonal basis, light winds (2 m sec^-1 or less) generally predominate in winter and summer, while spring and to a lesser extent, autumn, experience days with winds >2 m sec^-1.

Global solar radiation is the total incoming direct and diffuse short-wave radiation received from the whole dome of the sky on a horizontal surface, usually expressed as megajoule per square metre (MJ m^-2).  The annual average daily global solar radiation was relatively constant over the 1980-2001 period, ranging from 10.6 to 12.53 MJ m^-2. Monthly averages ranged from a low 2.41 MJ m^-2 in December to a high of 20.63 MJ m^-2 in June (Figure 5). The highest recorded value of daily solar radiation was 31.71 MJ m^-2 on June 4^th, 1982.