1. Introduction

• 1.1 Definition
• 1.2 Key Facts

2. Related Material

• 2.1 Important Physical Constants
• 2.2 Temperature Structure of the Atmosphere
• 2.3 Temperature Patterns of the Lower Atmosphere
• 2.4 Diurnal Patterns in Air Temperature
• 2.5 The Planetary Boundary Layer
• 2.6 Typical Aerodynamic Constants
• 2.7 Modeled Vertical Temperature Patterns
• 2.8 Aerodynamic Surface Temperature and Radiometer Measurement
• 2.9 Growing Degree Days (Thermal Time)

3. Instrumentation

• 3.1 Historical Instrumentation
• 3.2 Instrumentation

4. Local Charts

• 4.1 Local Temperature Chart
  

• Temperature is a fundamental control on most biological processes
  • Photosynthesis (Peak photosynthesis occurs at intermed. temperatures )
  • Respiration & Decomposition (Respiration increases with increasing temperature)
  • Enzyme activity & Growth
• Temperature is a fundamental limiting factor on organisms
  • Maximum temperatures
  • Minimum temperatures (Freezing)
• Temperature is a fundamental control on many physical/chemical processes
  • Weathering (Weathering rates are highest for moist, warm conditions)
  • Evapotranspiration

     

Peter Halasz, 3/3/07 with adaptions by Dar Roberts 3/20/08. Original image published at: http://en.wikipedia.org/wiki/Image:Lifezones_Pengo.svg This file is licensed under the Creative Commons Attribution ShareAlike license versions 2.5, 2.0, and 1.0

Holdridge Life Zone Concept (figure above)

Additional Information :

• Expressions of Temperature
  • Tk: Kinetic temperature. Temperature of an object due to molecular motion. The same temperature you would get by sticking a thermometer into something
  • Tr: Radiant temperature. Temperature retrieved based on radiant energy emitted by an object.
  • Tc: Color temperature. Temperature retrieved based on the peak wavelength of emission.
• Air temperature
  • Measure of the average kinetic energy of air molecules, usually referring to the quantity that would be measured by a thermometer exposed to the air but sheltered from direct solar radiation. Surface air temperature is usually measured at a standard height of either 1.5 or 2 meters above the ground (Ahrens 2007).
• Units of Temperature
  • Fahrenheit
    Linked to a freezing temperature of 32 F and boiling temperature of 212 F
  • Celsius
    Linked to a freezing temperature for water of 0 C and boiling temperature of 100 C
  • Kelvin
    Absolute temperature scale
• Conversions
  • C = (F-32)*5/9
  • K = C+273.16

Important Physical Constants:

• Specific Heat
• Volumetric Heat Capacity
  
  
  

Specific Heat (Cs):
The amount of energy required to raise 1 kg of an object one K.

Water: Cs = 4.1868x10^3 J kg-1 K-1
Dry air: Cs = 1.0x10^3 J kg-1 K-1

Specific Heat is important because:

• Dry materials have a lower specific heat, and thus change temperature more readily
• Moist or wet materials have a higher specific heat and thus change temperature less readily
• This is a major factor governing temperature variation between coastal and continental regions
• This is a major factor modifying temperature variation in the atmosphere, with higher humidity resulting in less variable air temperatures

Volumetric Heat Capacity (Cv):
Defined as the amount of heat required to raise a unit volume of a substance 1 K.

Cv=ρ Cs
Cv = Volumetric Heat Capacity (J m-3 K-1)
ρ = density (kg/m3)
Cs = Specific Heat

Typical values
Water: Cv = 4.1868x10^3 J kg-1 K-1*1000 kg/m3=4.1868x10^6 J m-3 K-1

Dry air: Cv = 1.0x10^3 J kg-1 K-1*1.25 kg/m3=1.25x10^3 J m-3 K-1

• Atmospheric structure is largely governed by temperature
• Radiation is the dominant process modifying temperature
• Key layers include the troposphere & stratosphere
• Adiabatic processes dominate in the lower troposphere

A change in the temperature of a parcel of air without a change in heat content.

Importance:
Governs the level in the atmosphere where condensation occurs (cloud base height)
Governs changes in temperature with elevation

• Recall PV=nRT
  • p(z)^γ-1/T(z)^γ = constant
  • γ = 1.4
• Dry Adiabatic Lapse Rate (DAR)
  • 9.8 C/1000 m
  • Derived by combining the hydrostatic equation with the ideal gas law
• Moist Adiabatic Lapse Rate (MAR)
  • Varies between 3 and 9.78 C/1000 m depending on humidit

• Determined by the rate of vertical temperature change relative to adiabatic cooling
• Four basic conditions exist
  • Inversion: Temperature increases with height
  • Stable: Temperature decreases at a lower rate than the adiabatic rate
  • Neutral: Temperature decreases at the adiabatic rate
  • Unstable: Temperature decreases faster than the adiabatic rate
• Unstable conditions promote vertical mixing.
• Stable conditions or inversion restrict vertical mixing

Unstable

Data Access: http://weather.uwyo.edu/upperair/sounding.html
Historical data from Park Williams

Data Access: http://weather.uwyo.edu/upperair/sounding.html
Historical data from Park Williams

Diurnal Patterns in Air
Temperature :

• Generally follows insolation
• Lapse conditions during the day
• Inversions at night
• Significant lags in the afternoon

The Planetary Boundary Layer:

• Describes the interface between the lower atmosphere and surface
• Commonly expressed as a change and wind velocity due to surface friction
• Modifies the exchange of moisture, trace gasses and heat between the surface and atmosphere
• Can be modeled using a Logarithmic Wind Speed Profile
  U(z) = u_**ln[(z-d)/z₀]/k
  • u* = friction velocity m/sec
  • z = height (m)
  • d = zero plane displacement height
  • k = Von Karmen’s constant (0.4)
• Key Point: Rough surfaces promote vertical mixing
• Unstable conditions promote vertical mixing. Stable conditions depress vertical mixing. Stability modifies the wind speed profile, making surfaces look “rougher” or “smoother”.

d = ~0.6h, where h = height (m)
z =~ 0.02h
Table values derived from Oke, Boundary Layer Climates, 1987 pg 57

Aerodynamic Temperature:

• Describes vertical temperature change across an atmospheric boundary layer
• T(z)= T(0) – H/(0.4*pCp*u*)*ln[(z-d)/z_h]
• Where
  • T(z) = Temperature at height z
  • T(0) = Aerodynamic surface temperature (at d+z_h)
  • H = Sensible Heat Flux (W m-2)
  • pCp = Volumetric heat capacity of air (1205 J m-3 C-1 at 15 C)
  • u* = friction velocity
  • z_h = roughness length to sensible heat flux
  • d = zero plane displacement height

Modeled Vertical Temperature Patterns

(See figure above)

T(z) = T(0) –constant*ln[(z-d)/z_h]
Y = mx+b
Constant = H/(0.4*pCp*u*)

Conifer (z0=3, d=15 m)
Crop (z0=0.3, d=1.5 m)
Grass (z0=0.06, d=0.3 m)
Soil (z0=0.01, d=0m)
When H negative (sensible heat flux away from the surface), air temperature decreases with increased height.
The pattern of decrease follows a log profile

Aerodynamic Surface Temperature and Radiometer Measurement:

• Aerodynamic Temperature at COPR
  T(d+z0) = T(75)-slope*ln[(75-60)/2]
  s lope = (T285-T75)/[ln[(75-60)/2)-ln[(285-60)/2]
  T(75) = Air Temperature at 75 cm sensor
  T(285) = Air Temperature at 285 cm
  d = 60 cm, z0=2 cm for a 1 m canopy
  
  Compared to T(0) from the net radiometer
  T(K) = [LWup/(σ*0.98)]^0.25

• Generally good to 15 C
• Under-predicts surface temperature at high temperatures
  Why? Recall d & zh

Growing Degree Days (Thermal Time):

Numerous plant processes are temperature dependent

• Net Primary Production (Gross - Maintenance)
  • Crop yields
  • Tree growth
• Germination, flowering and fruiting
• Ripening, Senescence
• Pest development

• Integral of average daily temperature above a base temperature
  GDD = Σ_i=1^days[(Tmax-Tmin)/2-Tb)*Δ t
• Typically calculated from weather data. Integral initialized from winter low.

Historical Instrumentation:

See: http://en.wikipedia.org/wiki/Galileo_thermometer
See: http://en.wikipedia.org/wiki/Mercury-in-glass_thermometer

HMP45C Temperature & RH Probe (Airstrip)
Utilizes Platinum Resistance Thermometer (PRT) which works on the principle of temperature dependent resistance to electrical currents through a fine platinum wire. Shielded from direct insolation.
Measurement Range: -40°C to 60°C;
Accuracy: ±0.3°C (0° to +40°C), ±0.5°C (-40°C to +60°C)

CS215 Temperature & RH Probe (COPR & Lisque)
Digital CMOSens® element for combined temperature and relative humidity measurement.
Measurement Range: -40C° to +70°C
Accuracy: ±0.4°C (+5° to +40°C), ±0.9°C (-40°C to +70°C)

Installing Temperature & Relative Humidity Sensor at Coal Oil Point;
Photo by Meri Marsh; May 25, 2007

Time: UTC
Units: °C