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Air Temperature and relative Humidity

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Current Conditions
Air Temperature (deg F) 49.0
Air Temperature (deg C) 9.4
Relative Humidity (%) 100.0
Last update: Sat Sep 23 02:10:01 2017 PDT

All real time data >

Air Temperature

Air temperature varies in daily, seasonal and annual cycles, and over longer time frames. Some temperature variation is cyclic, such as the Pacific Decadal Oscillation (PDO) motion and orbit of the Earth around the sun. Temperature change can affect plant productivity, animal life cycles and migrations, habitat, food sources, changing sea levels and weather patterns. By tracking temperature change over time, researchers can follow climate change and evaluate anthropogenic and environmental influences.

Relative Humidity

The water-holding capacity of air is determined by temperature, thus humidity levels must be measured relative to temperature, this measurement is described as relative humidity, expressed as a percentage. Relative humidity is a measure of the amount of water in the air compared with the amount of water the air can hold at that temperature. When a volume of air at a given temperature holds the maximum amount of water vapor possible, the air is saturated and the relative humidity is 100%.

Humidity levels are generally high near the coast, due to the wet ocean air. At the Bodega Marine Laboratory, foggy days are common, resulting in high levels of humidity. Fog is an significant source of precipitation in regions that do not have high annual rainfall.

Air temperature and humidity are measured with a temperature and humidity probe.

air temp f

air temp c

air temp c

rotronic sensorInstrument Type: Campbell Scientific CS215-L Temperature and Relative Humidity Sensor

Description:The CS215 probe uses a single chip element that incorporates both a temperature and RH sensor. Each element is individually calibrated with the calibration corrections stored on the chip. The probe is fitted with a low-cost sintered plastic filter to minimize the effects of dust and dirt on the sensor. The filter is lightweight and hydrophobic, thereby minimizing the effect of the time response of the sensor.

Location: Weather box, 40 m from coastal bluff
Latitude 38° 19' 01.52" N
Longitude 123° 04' 18.41" W

Installed: 16 October 2013 to current

Specifications: Humidity Sensor (CS215-L Temperature and Relative Humidity Sensor)
Range: 0 to 100% RH
Accuracy: 10% to 90% range: ±2% RH; 0% to 100% range: ±4% RH
Repeatability: 0.3% RH
Response Time: 20 sec

Specifications: Temperature Sensor (CS215-L Temperature and Relative Humidity Sensor)
Range: -40 to +70 °C
Accuracy: 25°C: ±0.3°C; +5° to +40°C: ±0.4°C; -40° to +70°C: ±0.9°C
Repeatability: 0.1 °C
Response Time: 120 sec

Acquisition Settings:
Instantaneous
Data stored at 5 second intervals

rotronic sensorInstrument Type: Rotronic MP101A Humidity Temperature Probe

Description: A thin-film, capacitive humidity sensor and a platinum resistance temperature detector housed in a radiation shield; temperature sensor used automatically to compensate for the effect of temperature on humidity measurements

Location: Weather box, 40 m from coastal bluff
Latitude 38° 19' 01.52" N
Longitude 123° 04' 18.41" W

Installed: 4 July 2003 - 16 October 2013

Specifications: Humidity Sensor (Rotronic Hygromer C94)
Range: 0 to 100% RH
Accuracy: 1% RH at 20-25 °C
Repeatability: 0.3% RH
Response Time: 10 sec

Specifications: Temperature Sensor (Pt100 RTD)
Range: -40 to +60 °C
Accuracy: 0.3 °C
Repeatability: 0.1 °C
Response Time: 10 sec

Acquisition Settings:
30 second running average
Mean value logged every 5 seconds
Data stored at 10 second intervals

Sensor Calibration and Quality Assurance Procedures

Instrument: Campbell Scientific CS215-L Temperature and Relative Humidity Sensor

Installed: 16 October 2013 to current

Calibration information not yet available.

Instrument: Rotronic MP101A Humidity Temperature Probe

Installed: 4 July 2003 - 16 October 2013

Temperature

Equipment: Primary Rotronic MP101A RHT Sensor S/N 90768
Secondary Rotronic MP101A RHT Sensor S/N 96628
Secondary Li-Cor LI-1400 Data Logger S/N DLA 2289

Procedure: The secondary temperature sensor is placed in the weather box near the primary sensor, so the two instruments are exposed to similar conditions. The secondary data logger is programmed with the appropriate logging routines for the secondary sensor. Power for the second instrument is tapped off the five volt supply of the main data logger. Data from the two sensors are then acquired simultaneously for a period of approximately one hour.

Sample Temperature Comparison

air temp comparison plot

Data from the two sensors are compared using Excel. The values measured by the primary sensor are subtracted from the values measured by the secondary sensor, to determine the difference between the two. Data from the primary sensor are considered good if the data sets agree within the manufacturer’s specifications of ± 0.3 °C for instrument accuracy.

Temperature measurements are also checked periodically with a spirit thermometer. Though the thermometer does not have the degree of precision of the Rotronic probe, it is a simple single point check.

Relative Humidity

Installed: 4 July 2003 - 2011

Equipment: Rotronic MP101A Humidity Temperature Probe S/N 90768
NOAA Humidity and Temperature Sensors
Compact Sling Psychrometer

Procedure: NOAA has a suite of meteorological sensors established at the Bodega Marine Reserve. Data from these sensors can be downloaded from the internet at http://www.etl.noaa.gov/et7/data/archive/UneditedActive/.
These data are used for sensor comparison by downloading a data set from an entire day.

Since NOAA data are logged at two minute intervals, BML data are also selected at two minute increments, but data are not averaged to determine the two minute mean of the 10 second data points. They are simply instantaneous values recorded every two minutes.

Sample Relative Humidity Comparison

qa rh

The two independent data sets are compared graphically in Matlab to look for general agreement. Any gross differences are investigated further. An average difference between the values measured by the two sensors is also calculated.

BML relative humidity measurements are considered good if the two data sets agree within 5%. Relative humidity is also checked periodically with a sling psychrometer. Though the psychrometer does not have the degree of precision of the Rotronic probe, it is a simple single point check.