Slide 1Boundary Layer DefinedSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Turbulent Heat FluxSlide 11Slide 12Slide 13Radiation DefinitionsSlide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Surface Energy BudgetSlide 26Slide 27Slide 28Slide 29Slide 30MicrometeorologyBoundary Layer MeteorologySurface Energy BudgetMicrometeorology is the study of the atmosphere near the surface and its associated turbulence and transport of scalars. It deals with the small horizontal and short temporal scales of motion in meteorology. Typically, less than 1 km and 1 hr. The atmospheric boundary layer is formed as a consequence of the interactions between the atmosphere and the surface of earth. Micrometeorologists study these interactions.A variety of instrumentation is used to measure the atmospheric boundary layer and related turbulence. Stull: Chap: 4 and W&H chap: 9Boundary Layer Defined•A boundary layer is the layer next to a physical boundary such as the inside wall of a pipe. In our case the earth’s surface. •Transport processes modify the lowest 100 to 3000 m AGL (above ground level) of the troposphere creating the boundary layer.•The atmosphere above the boundary layer is called the free atmosphere, typically. •The boundary layer air separates the atmosphere from the earth’s surface. Actually, the atmosphere really doesn’t know that the earth is below it.Planetary Boundary LayerPlanetary Boundary LayerThe layer of air influenced by surface friction is called the The layer of air influenced by surface friction is called the planetary boundary layerplanetary boundary layer (PBL). (PBL). Define the boundary layer as that part of the troposphere Define the boundary layer as that part of the troposphere that is directly influenced by the presence of the earth’s that is directly influenced by the presence of the earth’s surface, and responds to surface forcings with a timescale of surface, and responds to surface forcings with a timescale of ~ 1 hr or less.~ 1 hr or less.Pollutants in the Atmospheric Boundary Layer05001000150020002500300035004000450050000 2 4 6 8 10 12 14 16 18300 305 310 315 320 325Water Vapor Mixing Ratio (g kg-1)Potential Temperature (K)05001000150020002500300035004000450050000 90 180 270 3600 5 10 15 20Wind Direction (degrees)Wind Speed (m s-1)5 August 2006 Evening (6 PM) University of Houston Sounding0700 CDT0700 CDT10001000130013001600160019001900University of Houston 26 Sept 2006University of Houston 26 Sept 2006What is turbulence?•Simply defined as perturbation from the mean.( )u u u�= +Background: definitions( )u u u�= +How do we measure u′?A sonic anemometer measures at very high sampling rates. This is typically at 10 or 20 Hz. Data from a high temporal resolution time series is used to calculate the mean of the time series and subsequently a perturbation from the mean.Once the perturbations are calculated, turbulent statistics can be calculated.uuu Net upwardheat flux10 11 1cov( ) ( ) ( )N Ni ii iw W W w wN Nq q q q q-= =�� ��= - � - = =� �Turbulent Flux?• Transport of a quantity by eddies or swirls.• The covariance of a velocity component and any quantity.´= +w´= +EddyMixes some air downAnd some air upz´= neg. w´= neg. 0Turbulent Sensible Heat FluxTurbulent Heat Flux•Sensible Heat Flux:•Latent Heat Flux:H pQ c w Tr��=E vQ L w q��=VarianceOne statistical measure of the dispersion of data about the mean is the biased variance1022)(1NiiAANIt is a good measure of the dispersion of a sample of BL observations. However, recall that 21022)(1aaNNiiAAa Substituting this into the biased definition of variance:• is a measure of the intensity of turbulence• simply the summed velocity variances TKE e u v w 122 2 2Turbulence Kinetic Energy (TKE)Radiation DefinitionsRadiation flux: is the amount of radiation coming from a source per unit time in W.Radiant intensity: is the radiant flux leaving a point on the source, per unit solid angle of space surrounding the point. [W/steradian]Radiance: is the radiant flux emitted by a unit area of a source or scattered by a unit area of a surface.[W m-2 sr-1] Irradiance: is the radiant flux incident on a receiving surface from all directions, per unit area W m-2.Absorptance, reflectance, transmittance: fractions of the incident flux that are absorbed, reflected, or transmitted by a medium.Global Solar radiation: is the solar irradiance received on a horizontal surface [W m-2]. This is the sum of direct solar beam plus the diffuse component of skylight, and is the physical quantity measured by a pyranometer.Radiation DefinitionsVisible Radiation: is the spectral range of the standard observer. Most of the visible radiation lies between 400 nm and 730 nm.Ultraviolet Radiation: is the radiation with wavelengths in the range 100 to 400 nm. It is subdivided into three ranges: UVA is 315-400 nm, UVB is 280-315 nm, and UVC is 100-280 nm. Infrared Radiation: is the radiation with wavelengths longer than 730 nm.Radiation DefinitionsDirect solar radiation: is the radiation emitted from the solid angle of the sun’s disc, received on a surface perpendicular to the axis of this cone, comprising mainly unscattered and unreflected solar radiation. At the top of the atmosphere this is usually: 1367 W m-2 . The direct solar radiation at the earth’s surface is the physical quantity measured by a pyrheliometer. Diffuse Solar Radiation: (Sky radiation) is the downward scattered and reflected radiation coming from the whole hemisphere. Diffuse radiation can be measured by a pyranometer mounted in a shadow band.Radiation DefinitionsPhotosynthetically Active Radiation (PAR): is the band of solar radiation between 400-700 nm that plants use in the photosynthesis process. PAR is usually expressed in moles of photons, a mole being Avogadro’s number of photons, 6.022 x 1023 photons. Albedo: is the fraction of incoming solar radiation to reflected solar radiation.α = SWreflect / SWincomingMethods of MeasurementTwo primary methods in the measurement of radiation:Thermal detection: response to heat gain or loss due to absorption of incoming or emission of outgoing radiation. Photovoltaic detectors: convert absorbed radiation to a voltage. Shortwave or solar radiation is defined to be 0.3 μm to 4 μm BUT since high-quality glass windows are transparent from 0.3 to 3 μm,