Atmosphere Structure
What drives winds?
Pressure gradients. Air moves towards areas of low pressure
How do sea and land breezes form?
The land heats and cools more slowly than the sea, so during the day, low pressure over the land causes sea breezes. At night, low pressure over the sea causes land breezes
Name a couple large scale effects of El Niño events
Weakened monsoons in S. Asia, increased California rains
Adiabatic process
Not adding or removing any heat
What is the Boundary Layer?
The lowest part of earth's atmosphere (up to about 1km) - most strongly influenced by the surface, it's friction, radiation, and turbulence
Name the four layers of the atmosphere
Troposphere (0-15 km)
Stratosphere (15-50 km)
Mesosphere (50-80 km)
Thermosphere (80-480 km)
Jet streams
Bands of strong, approximately geostrophic winds blowing W->E (westerly) high in the troposphere. There are Polar Jets at 60 degrees, and Subtropical Jets at 30 degrees. Blow upwards of 200 km/hr.
What is ENSO?
El Niño-Southern Oscillation: a dominant, coupled (ocean & atmospheric) natural form of large scale climate variability with a period of 2-7 years. It is the change in strength of the Walker Circulation. El Niño is the oceanic component. Southern Oscilation is the atmospheric component
Hydrostatic balance
The balance between the downward force of gravity and the upward pressure gradient force in an air column. Expressed as -ρg = Δp/Δz
How do wind speeds change with height in the boundary layer?
Wind speeds increase logarithmically with height in the boundary layer. Roughness length is the theoretical height at which wind speeds drop to 0. Up to 2m in cities and as low as 1cm above snow
How does temperature change with height in the different layers?
Troposphere - temp decreases with height (heated from below by IR radiation from the ground)
Stratosphere - temp increases with height (heated from above by the ozone layer)
Mesosphere - temp decreases with height
Thermosphere - temp increases with height
Walker Circulation
Longitudinal convection cells which form because of the different heating of land types and ocean
El Niño vs La Niña
Both are concerned with sea surface temperatures in the Eastern/Central Pacific. El Niño is when this area warms due to a weakening of the Walker Circulation. La Niña is when this area cools due to a strengthening of the Walker Circulation which causes upwelling of deep cold waters
Dry adiabatic lapse rate (DALR)
Derived from the first law of thermodynamics, considering that an air parcel does on the atmosphere (against gravity) as it rises and must balance this by changing its internal energy. δT/δz = g/cp (gravity over specific heat while controlling for pressure). 9.8 C/km - as air rises it expands and cool
What is the surface energy balance?
Net radiation can be expressed as a balance of incoming and outgoing solar (shortwave) and infrared (longwave) radiation. Can also be expressed as a the sum of latent and sensible heat minus ground flux heat
The Intertropical Convergence Zone (ITCZ)
Since there is a surplus of energy in the tropics, warm air rises because of convection, air from either side whooshes in to fill the low pressure zone (CONVERGENCE). Very wet, but not too windy (called the doldrums). The ITCZ wobbles a bit based on the season and where the most incoming solar radiation is hitting
Explain the seasonal variation in the strength of weather patterns
There is strong seasonality in the Northern Hemisphere because land masses create lots of variation as land and ocean heat/cool at different rates. Winter circulation is always stronger because there are stronger low pressure systems, because sinking air is colder and higher pressure
How is ENSO measured?
By sea surface temperature anomalies or by the southern ocean index which is the difference in pressures in Darwin, Australia and Tahiti
Equivalent Potential Temperature
Potential temperature (the temperature an air parcel would be if it was moved to a reference pressure via adiabatic processes)+ the latent heat that would be released if all the water was condensed out of it. Regions of high equivalent potential temperature are often very moist and unstable
What drives turbulent kinetic energy (TKE)?
Driven by: advection (wind speeds), mechanical (wind shear), buoyancy (air rising), transport (by turbulence itself), and dissipation (destruction of turbulence by viscosity of the medium
Hadley cells: energy surplus in tropics -> air rises and spreads out at the tropopause, dries and cools sufficiently to sink around 30 N &S. Warms as it sinks. Creates high pressure zone at the surface where the air is forced to diverge
Polar cells: cool air sinks at the poles and diverges -> meets warm winds at 60 degrees and forces them to rise over the polar front
Ferrel cells: balance the system
Why do winds spiral around pressure systems rather than circling them as would be expected by geostrophic balance?
Friction acts on the system, adding a third force. The actual wind blows somewhere between the geostrophic wind and the PGF, so spirals in toward low pressure systems. ie close to the surface, winds blow across isobars at a small angle
What is the name of my mom's high school friend's dog that recently had CCL surgery?
Enso
Atmosphere stability: what does it mean for the atmosphere to be stable or unstable?
The atmosphere is stable when an air parcel moving dry adiabatically does not continue to rise once it starts rising. The atmosphere is unstable if potential temperature decreases with height (cools faster than the DARL) beacause our air parcel will always be warmer than the surrounding atmosphere. The atmosphere is neutrally stable if potential temperature is constant with height. And the atmophere is absolutely stable if potential temperature increases with height beacuse the air parcel will be forced to sink
Describe the structure of the boundary layer over the course of the day
All changes in temperature start at the surface and work their way up. During the day, the ground heats (if there's sun) and the boundary layer deepens, rising at the DALR, and mixes because turbulance is driven by buoyancy. Cumulous clouds sit atop the mixed layer. Right at the surface, the surface layer can be humid and superadiabatic. At night, the ground cools and becomes stable because potential temperature increases with height. This means that pollutants and fog can get trapped at the surface. The new nocturnal stable layer pushes the old mixed layer up, making it become the "residual layer." Above everything is the entrainment/capping inverstion which is also stable. There is more mixing in the summer (hotter & more daylight). Near zero wind