Surface Energy Balance (1)

Review of last lecture The mission of meteorology is to understand and predict weather- and climate-related disasters (e.g. tornados, hurricanes, El Nino and global warming). The modern climatology (meteorology) was born in the 1940s (a very young science!), but has been growing very fast! Now we have a global observational network with many satellites, ships, radars and surface stations, as well as very comprehensive prediction models running on the world’s largest computers. The current status of weather and climate predictions: (1) weather prediction good to 10 days, (2) tropical cyclone prediction good in track but not in intensity, (3) climate prediction good to two seasons, (4) climate change projections have a 3-fold difference in magnitude. The main reasons of the difficulties: (1) Teleconnection problem, (2) Feedback problem, and (3) Subgrid-scale problem. Importance of the ABL: (1) interface between atmosphere and ocean/land/ice - flux transfer and feedback, (2) the human beings are living in the ABL and change the environment, (3) a basic subgrid- scale process

Energy: the ability to do work Many forms: electrical, mechanical, thermal, chemical, nuclear, … Joule (J): standard unit of energy (1 J= calories) Watt (W): rate of energy flow (W = 1 J/s) Energy basics

Methods of Energy Transfer Conduction –Molecule to molecule transfer –Heat flow: warm to cold –e.g. leather seats in a car Convection –transferred by vertical movement –physical mixing –e.g. boiling water Radiation –propagated without medium (i.e. vacuum) –solar radiation provides nearly all energy –The rest of this chapter deals with radiation

Radiation Everything continually emits radiation Transfers energy in waves Waves are both electrical and magnetic, hence electromagnetic radiation

Radiation Quantity and Quality Quantity: how much?  wave height (amplitude). Hotter bodies emit more energy than colder bodies Quality: what kind?  wavelength: distance btw. crest and crest (or trough and trough). generally reported in μ m (microns)- one millionth of a meter. Hotter objects radiate at shorter wavelengths Travels at the speed of light (300,000 km/s). It takes 8 minutes for light from the Sun to reach Earth, and 4.3 years for light from the next nearest star, Proxima Centauri to reach us.

The Electromagnetic Spectrum The limitations of the human eye!

A man detected by different instruments Infred device Bare eyes X-rayMicroscope

Sun Wavelength of Sun and Earth Radiation Sun = “shortwave” ( μm) Peak 0.5 μm (green) Earth = “longwave” (4-100 μm) Peak 10 μm (infrared)

Satellite Measurements of the Earth ’ s Radiation Budget NASA’s Earth Radiation Budget Satellite (ERBS)

Earth ’ s energy budget (averaged over the whole globe and over a long time) At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwave At the surface:At the surface: Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave + Latent heat flux + Sensible heat flux + Subsurface Diffusion + Latent heat flux + Sensible heat flux + Subsurface Diffusion Sensible heat 7% Latent heat 23% Net Longwave 21% Yellow: shortwave Red: longwave

Net Radiation At the top of the atmosphere, radiation is balanced, i.e. (SW + LW = Net = 0) At the surface, on the contrary, radiation is not balanced, i.e., (SW + LW = Net Radiation).

tropic-to-tropic – energy surplus poles – energy deficits ~ 38 o N/S – balance imbalance of net radiation at surface  Equator/Tropics vs. high latitudes drives global circulation agents: wind, ocean currents, weather systems Latitudinal Variations in Net Radiation

Seasonal and diurnal variations in net radiation Seasonal variation Seasonal variation Summer: energy surplus Summer: energy surplus Winter: energy deficits Winter: energy deficits Diurnal variation Diurnal variation Day: energy surplus Day: energy surplus Night: energy deficits Night: energy deficits

Seasonal variation of surface radiation

Earth ’ s energy budget (averaged over the whole globe and over a long time) Sensible heat 7% Latent heat 23% Net Longwave 21% Yellow: shortwave Red: longwave At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwave At the surface:At the surface: Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave + Latent heat flux + Sensible heat flux + Latent heat flux + Sensible heat flux

Summary –What is energy? 3 methods of energy transfer –The names of the 6 wavelength categories in the electromagnetic radiation spectrum. The wavelength range of Sun (shortwave) and Earth (longwave) radition –Earth ’ s energy balance at the top of the atmosphere. Incoming shortwave = Reflected Shortwave + Emitted longwave –Earth ’ s energy balance at the surface. Incoming shortwave + Incoming longwave = Reflected shortwave Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave + Latent heat flux + Sensible heat flux + Emitted longwave + Latent heat flux + Sensible heat flux + Subsurface conduction