Overview
Meteorological conditions (the weather) directly impact the physical and biological condition of lakes and tributaries. Some of the most immediate changes are seen in tributaries which often respond rapidly to changes in precipitation, temperature and solar insolation. Changes in wind speed and direction can frequently be seen in the shape of a lake’s temperature profile. Monitoring these data is important in quantifying changes within lakes or tributaries.
Air Temperature
Air Temperature is measured using a method similar to the measure of water temperature. The air temperature probe is enclosed in a radiation shield (to protect the probe from direct sunlight) and is mounted on a mast above the buoy.
Air temperature contributes to thermal stratification of a lake. It also influences the temperature of tributaries.
The effect of air temperature will be seen most readily in the temperature of Onondaga Creek.
Wind Speed and Direction
 Wind Speed is measured in units of m/s (meter per second) and wind direction is measured in degrees from north using an anemometer. The anemometer consists of propeller attached to a weather vane which keep to propeller pointing into the wind and also allows for the measurement of wind direction. The anemometer is position at the top of a two meter pole located on top of the buoy. The wind moving past the propeller causes the propeller to rotated. The number of rotation per unit time of the propeller is calibrated to wind speed. The position of the weather vane to the north pointing bearing establishes the wind direction.
Wind velocity (wind speed and direction) determines a lake’s thermal structure. Typically higher wind speeds create larger waves and increase turbulence in the upper waters of a lake. This can lead to the deepening of the thermocline or during time of weak stratification can lead to turnover. Wind driven waves can increase shoreline resuspension of sediments which can effect turbidity levels, increase the available nutrients, and possible introduce toxic sediments into the water column. Below the lake surface, higher wind speeds can induce a tilting of the thermocline with subsequent internal wave generation that can lead to bottom resuspension. If thermocline tilt is large, an upwelling could occur resulting in metalimnetic and hypolimnetic waters reaching the surface layer. An upwelling event occurred in Onondaga Lake on September 11, 2002. Strong sustained winds blowing out of the northwest along the major axis of the lake produced an upwelling event that was responsible for a large fish kill in the northwest section of the lake. The upwelling of anoxic, reduce species rich hypolimnetic water reduced the oxygen concentration to near zero throughout the water column in the north end of lake.
Relative Humidity
Measured in units of percent saturation. The probe utilizes a material that changes its dielectric properties which enhances its capacitance as it absorbs moisture.
Humidity can be expressed as relative (to saturation of water in air) which is a temperature dependent measurement similar to expressing dissolved oxygen as percent saturation. Thus changing the temperature will change the relative humidity since warmer air can hold more water vapor. Humidity can also be expressed as a dew point temperature, which is the temperature at which saturation or condensation will occur. Specific humidity, expressed as grams of water vapor per kilogram of moist air, is a measure of the actual amount of water vapor or moisture in the air, regardless of the air's temperature.
Relative humidity is an import factor in evaporation. Evaporative cooling from a surface of a lake or stream is one of the mechanisms which effects its heat budget
Solar Irradiance
Solar irradiance is measured in units of w/m2 (watts per square meter) using a pyrometer. The pyrometer is mounted on meteorological station pole. The sensor uses a photodiode that creates an electrical current that is calibrated to the amount of radiation falling upon the sensor.
Quantifying solar irradiance is important in establishing heat budgets and well as in photosynthesis.
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