Humidity as an Abiotic Factor at Race Rocks

Humidity as an Abiotic Factor at Race Rocks

The present Humidity measured by a sensor 1.5 metres above the rock surface at Race Rocks. Humidity in concert with Temperature, Sunlight and Wind is an important factor which all organisms have to tolerate or adjust to at Race Rocks. The humidity changes widely in a number of micro ecosystems, even in the intertidal area, such as in crevices and under vegetation.
humidity humidity humidity
Graph of today’s humidity at Race Rocks. The humidity for the past week. Click on the above graphs for larger versions The preceding month humidity record . These three graphs represent historical records of atmospheric pressure at different time scales. This graphical interpretation is made possible by the website

The following are some of the derived variables which involve humidity in their calculations. For an Advanced explanation of the derived variables such as wind chill, ET, heat Index, etc. See this link.

The present Heat Index, calculated from sensors 1.5 metres above the rock surface at Race Rocks. Data: Heat Index
The Heat Index, also knows as the Temperature/humidity index (THI) uses the temperature and the relative humidity to determine how hot the air actually “feels.” When humidity is high (i.e., the air is saturated with water vapor) the apparent temperature will be higher than the air temperature because perspiration cannot readily evaporate into the surrounding air.
Technically, Heat Index is calculable only when air temperature is above 68 °F (20 °C) because it is a measure of heat stress, which is not significant at lower temperatures. Davis Instruments smoothes the curve relating air temperature to Heat Index between 68 ºF (20 ºC) and 57 ºF (13.9 ºC). Below 57 ºF (13.9 ºC), the Heat Index is equal to outside temperature. Conversely, 135 °F (52 °C) is the highest Heat index for which calculation factors are available. Note that at very low humidity values, the air temperature can be as high as 140 ºF.
In terms of storage to the data logger and database, Heat Index is a special case. It is not stored in archive memory or in the database, rather it is calculated as necessary (for example, when plotting or displaying database information). When Heat Index data is needed, the software calculates an average for each archive interval based on the temperature and humidity readings for the archive period.

The Temperature Humidity Wind Index as calculated from sensors 1.5 metres above the land surface at Race Rocks. THW: Temperature Humidity Wind Index:

The THW Index uses humidity, temperature and wind to calculate an apparent temperature that incorporates the cooling effects of wind on our perception of temperature.
The THWS Index uses humidity, temperature, the cooling effects of wind and the heating effects of direct solar radiation to calculate an apparent temperature.
ET – Evapotranspiration
This is the amount of moisture evaporated off the surface.  Using this data with rainfall, one can determine moisture deficits/surpluses.
It has been calculated based on the temperature/rainfall data as measured at 1.5 metres above the rock surface at Race Rocks. See the Rainfall/ Precipitation Page.
The present dew point at Race Rocks, measured at 1.5 metres above the rock surface. See the Temperature Data page. The Dew Point:
Dew points indicate the amount moisture in the air. The higher the dew points, the higher the moisture content of the air at a given temperature. Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content) in order to reach saturation. A state of saturation exists when the air is holding the maximum amount of water vapor possible at the existing temperature and pressure.
When the dew point temperature and air temperature are equal, the air is said to be saturated. Dew point temperature is NEVER GREATER than the air temperature. Therefore, if the air cools, moisture must be removed from the air and this is accomplished through condensation. This process results in the formation of tiny water droplets that can lead to the development of fog, frost, clouds, or even precipitation.
Relative Humidity can be inferred from dew point values. When air temperature and dew point temperatures are very close, the air has a high relative humidity. The opposite is true when there is a large difference between air and dew point temperatures, which indicates air with lower relative humidity. Locations with high relative humidities indicate that the air is nearly saturated with moisture; clouds and precipitation are therefore quite possible. Weather conditions at locations with high dew point temperatures (65 or greater) are likely to be uncomfortably humid.

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