Wednesday, July 22, 2015

Composition & Structure of the Atmosphere


Introduction
·       Meteorology = the study of the atmosphere and the processes (such as cloud formation, lightning and wind movement) that cause what we refer to as the “weather”
·       Weather is distinct from climate in that the former deals with the short-term phenomena and the latter with the characteristic long-term patterns.


The Atmosphere, Weather and Climate
·       Atmosphere = a mixture of gas molecules, small suspended particles of solid liquids, and falling precipitation. 
·       Climatology
o   Relies on averages taken over a number of years in order to gauge typical atmospheric conditions for locations across Earth’s surface.
o   Also want to know about variability of the weather elements.
o   Frequencies of occurrences of weather events (such as extreme heat, hail or lightning) are also aspects of climates.
o   Concerned with changes in Earth’s climate and the factors responsible for those changes.


Thickness of the Atmosphere
·       ­How high is the sky?
o   There is no definitive answer. However, because Earth’s atmosphere becomes thinner at higher altitudes, even at heights of several hundred kilometers above sea level, there is some air and, hence, an atmosphere. But we have no way to establish its upper boundary because there is no universally accepted definition of how much air in a given volume constitutes the presence of an atmosphere.
Horizontal Winds
Vertical Winds
-       Primary motion over large areas
-       Are typically hundreds to thousands of times greater than vertical wind speeds
-       Hardest to detect and forecast
-       Determine much of the atmospheric behavior


Composition of the Atmosphere
·       The atmosphere is composed of a mixture of invisible gases and a large number of suspended microscopic solid particles and water droplets.
·       Molecules
o   Molecules of gases can be exchanged between the atmosphere and the Earth’s surface by physical processes (i.e. volcanic eruptions) or by biological processes (i.e. plant and animal respiration).
o   Can be produced and destroyed by purely internal processes (i.e. chemical reactions between gases)
o   Steady State / Equilibrium Condition = input rate is equal to the output rate
o   Dynamic Equilibrium = molecules cycling in and out of the atmosphere
o   Residence Time = average length of time that individual molecules of a given substance remain in the atmosphere

·       Homosphere
o   The lowest 80 km (50 mi) of the atmosphere
o   Vertical motions are more important than gravitational settling thus processes (other than settling) under gravity must explain any variations present.
o   Reflects the homogenizing role of wind and other motions
o   Gases are often categorized as being permeant or variable, depending on whether or not their concentration is uniform.
§  Permanent Gases = found everywhere in nearly the same proportion.
§  Variable Gases = distribution is uneven in both time and space.
·       Heterosphere = layer of the atmosphere (above the homosphere) where gases segregate according to molecular weight
·       Permanent Gases
o   Make up more than 99% of the atmosphere
o   Nitrogen (most abundant gas)
§  78% of all permanent gasses volume or 75.5% of their mass
§  Largely unreactive
§  Occurs primarily as paired nitrogen atoms bonded together to form single molecules denoted N2
§  Isotopes = variants of an element with different neutron counts
o   Oxygen (second most abundant gas)
§  21% of the volume of the atmosphere and 23% of its mass
§  Crucial to the existence of virtually all forms of life
§  Dynamic Oxygen = paired oxygen atoms
o   Nitrogen + Oxygen = 99% of all permanent gases
·       Variable Gases
o   Water vapor (most abundant) is 1% of the total volume
§  Condenses to a liquid at relatively low levels in the homosphere
§  Not uniformly distributed with altitude—at higher altitudes, water vapor is even more rare
§  Hydrologic Cycle (water cycle)
§  Source of moisture to form clouds

§  Very effective absorber of energy emitted by the Earth’s surface (radiant energy) thus making it one of the “greenhouse gases”

Tuesday, July 21, 2015

Adiabatic Lapse Rates

What do you know about the Wet Adiabatic Lapse rate?
-       Less than dry adiabatic lapse rate

The more it slants = greater lapse rate
 
Lapse rate = Rate of cooling


What’s the difference between the Dry and Wet Adiabatic Lapse Rate?
-   Unsaturated à reaches LCL à Saturated
-   Latent “Hidden” heat - The heat either released or absorbed as a result of a change of state.

-   When a cloud forms….
o   The water vapor reaches the LCL à Temperature decreases à It’s doing work à slows the rate of cooling
-   Water vapor condenses à latent heat is released
Mixing ratio (w) - A measurement of the amount of water vapor in the air of a given sized quantity of dry air. Grams of vapor per kilogram of dry air.

W = Water vapor in the box
-   Dewpoint Lapse Rate = As it goes up it decreases = 2 deg C / km


-   Dew point (Td) - The temperature to which air must cool at constant pressure in order for air to reach saturation (commonly dew to form); indicates moisture content.

Adiabats & Potential Temperature

Dry Adiabat = 333
·         Potential Temperature – A measure of heat. It is the temperature air would be if brought dry adiabatically to 1000 mb.

·         How much warmer will the potential temperature increase?
o   Has hidden heat, Lift up, pressure decreases, starts expanding, starts making hidden heat into real heat, which is determined by how much latent heat is left in the parcel
o   Wet adiabatic line will be parallel to the dry adiabatic line
§  Vapor starts condensing which makes latent heat turn into real heat
·         Latent heat becoming real is what is increasing the potential temperature -  delta = measure of real heat







Atmospheric Stability & Instability

Stability & Instability

·         Instability - Possessing the ability to move away from the original position; allows convection and enhances vertical motions.
·         Stability - Possessing the ability to return to its original position; suppresses convection.
·         Inversion - Temperatures increasing with increased altitude, or height. A negative lapse rate.
·         Lapse rate (Γ) - The change of temperature with a change in height. Rate of decrease in temperature. Getting colder with height = Positive lapse rate. dT / dZ = temperature changing with height.

 



·         Adiabatic – not heat
·         Isotherm – A line of constant temperature.
·         Isothermometer – A line of constant dew point temperature.
·         Barometer - measures pressure



 








Air Parcel’s
·         “Blob” of air
·         Expands and contracts freely
·         Rises and sinks through the atmosphere
·         If it is warmer it is less dense then the air which makes it rise (compression)
·         If it is colder it is more dense then the air which makes it sink (expansion)
·         Temperature will change from pressure – does not exchange from inside and outside the box
·         Temperature is NOT a measure of heat
  

Types of Heat Transfer
1.    Conduction
a.    The transfer of sensible heat from a warm object to a cool object through contact
2.    Convection
a.    fluid/anything that is flowing
3.    Radiation

How Pressure changes with height?
a.    dp / dZ < 0
b.    Pressure decreases with height, which is a negative change, that is less than

1st Law of Thermodynamics
̶        Heat In = Work + delta-T
a.    Adiabatic process:        





Warm air is less dense then cold air ONLY at the same pressure