Sep/6 ______________________________________________________________________ ___ ● Introduction to the Atmosphere and Measurements ○ The atmosphere is a thin, gaseous envelope held to the surface of the Earth by gravity ○ Upper atmosphere ‘tails off’ into interplanetary medium ■ 99% of the atmosphere is below 30km ■ 50% of the atmosphere is below 5.6km ■ The atmosphere weighs approx. 5.6 quadrillion tons ● What are the principal permanent atmospheric gases? ○ Nitrogen 78% ○ Oxygen 21% ○ Argon 0.9% ● Below 85km, these gases are homogeneously mixed, this region is known as the homosphere ○ Many other gases are present in the air. Two of the most important are Water Vapor and Carbon Dioxide ● Important gases with variable concentrations: water vapor ○ Meteorological significance of water vapor: ■ Condenses to form clouds, which can produce precipitation and impact how much sunlight reaches the surface ■ Absorbs radiant heat (infrared) passing through the atmosphere, thereby affecting atmospheric temperatures ■ Releases a large amount of heat during phase change (latent heat), which is an important source of atmospheric energy, especially for storms ● Continued: carbon dioxide ○ Mixing ratio of CO2 is increasing. Currently it's about 400ppm ○ Meteorological significance: ■ Absorbs radiant heat (infrared) passing through the atmosphere, effects atmosphere temperature ■ Carbon dioxide is produced via the decay of vegetation, volcanic activity, combustion of carbon containing fuels, etc. ● Continued: ozone ○ Ozone concentrations are highest in the upper atmosphere (the stratosphere) ○ High ozone amount contributes to smog ■ Ozone low = bad ■ Ozone high = good Sep/9 ______________________________________________________________________ ___ ● The three key state variables ○ Temperature ■ It is an indirect measure of the amount of energy contained within a system of interest ■ Temperature scales are defined once we decide on the temperatures of two reference fixed points, such as those of letting ice and boiling water at mean sea level ■ Celsius = 5/9 (F - 32) ■ Kelvin = C + 273.15 ■ A temperature of 0 K is called absolute zero; atoms and molecules possess theoretically no thermal motion ■ Weather balloons = rawinsonde ○ Pressure ■ Atmospheric pressure is due to the weight of the overlying air, which is given by the weight of the overlying air per unit surface area is expressed in millibars (mb) ■ The value of the standard atmospheric sea level pressure is 1013.25mb, which is equivalent to 14.7 lb/sq. In. ■ Pressure decreases nonlinearly with increasing altitude (equal in all directions) ○ Density ■ The air density also decreases with height ■ Gas density is defined as the amount of a gas present in a specified volume ■ Mass per unit volume, e.g., kg/m cubed ■ Gas density measures the concentration of a particularly gas ● State variables can be related by the : ideal gas law ○ P = 2.87 p x T ○ Where p in mb, p in kg/m cubed, T in kelvin ○ At the same pressure cold means more dense and warm means less dense ● Troposphere is the lowest layer of the atmosphere (closest to Earth) ○ Most of the weather happens ○ It’s height isn’t constant (equater v. poles) ○ Tropopause (between troposphere and stratosphere) Sep/ 11____________________________________________________________________ ____ ● The stratosphere contains the ozone layer, which absorbs harmful UV rays ○ Most of the ozone is found in the bottom of the stratosphere ● UV absorption causes heating of the air, the temperature in the middle and upper stratosphere increases steadily ● The atmosphere lies above the stratosphere ○ Extends from the stratosphere up to the mesopause ○ There is a shall isothermal zone at the bottom of the mesosphere ● Exopherse - 300 miles above the earth, interplanetary medium ● Additional measurements for the atmosphere ● Surface measurements are collected hourly ~100km spacing ○ Temperature, pressure, wind, humidity ● Balloon are release twice daily (typically ppz and 12zz) ~400km spacing ● Radars-- emits long wave radiation that can be scattered ○ Nexrad- net generation radar - doppler effect ● Satellites ○ Satellites view the atmosphere from orbit around the Earth ○ Three main types: visible, infrared, water vapor ○ Some satellites are geostationary, they orbit one place (don’t move) ○ Polar orbiting satellites - pole to pole rotations, always different global coverage ● Energy and Radiation ● Types of energy ○ Kinetic energy - anything that is moving has kinetic energy ○ Potential energy - energy that could become kinetic or move ○ Internal energy - molecular bonds (the energy that exists between elements when they are bonded, like O2) ○ Latent energy - phase changes, something going from a liquid to a solid, etc. Sep/ 16____________________________________________________________________ ____ ● Conduction occurs when energy is transferred from molecule-to-molecule through a substance. The molecules must be in contact for heat to be transferred efficiently ○ Surface air is heated/cooled by conductive heat transfer from/to the underlying ground ● Vertical air transport is called convection ● Horizontal air transport is called advection ○ Convection and advection occur in both gases and liquids ● Latent energy release tends to warm the surroundings ● Latent energy uptake tends to cool the surroundings ○ Vapor to liquid is called condensation ○ Liquid to vapor evaporation ○ Going from a vapor to a solid is deposition ○ Solid to a vapor is sublimation ● Radiant Energy ○ Doesn’t need molecules can pass through the vacuum (like space) ○ Electromagnetic waves at 11.8 inches/nano second ○ Radiant energy can be partially or completely absorbed by an opaque medium, reflected, transmitted by a transparent medium, and scattered at surfaces ● The stefan-boltzmann constant tells us how much energy is released by temperature ○ Tells us how much radiant energy is emitted but nothing about the kind of radiant energy ● Wilhelm Wien provides us with how the maximum emissions occurs at a wavelength that decreases as the temperature of the emitter increases ● Scattering ○ Blue light is most efficiently scatterings ○ Hence the sky is blue and the sun is yellow/orange ● Albedo - the fraction of light that hits something and bounces back ○ The absence of clouds on the moon causes the albedo to be so different ● Humidity - refers to the moisture content of the air, how much water vapor is mixed in with the air ○ Evaporation of liquid water adds water vapor to the atmosphere ○ Condensation returns water vapor to the liquid phase (fog) ● Water on Earth ○ Atmosphere 0.001% ○ Oceans 97.27% ○ Polar and Greenland Ice Caps 2.13% ○ Groundwater rivers, lakes, etc. 0.63% ● A mixing ratio is the ratio of the mass of a substance in an air parcel to the mass of the dry air in the parcel ● The amount of water vapor can also be expressed in terms of its vapor pressure (or partial pressure) which is the contribution it makes to the total pressure ● According to Dalton’s Law, the sum of the partial pressures is equivalent to total pressure ● The relative humidity is a fraction of the water that is in the air relative to the saturation ● As temperature goes up, the relative humidity goes down ● As temperature goes down, the relative humidity goes up ● Melanchivik changes about 100,000 years (tilt/the x-axis) ● Mixing ratio - ratio of the water compared to the air ● Relative humidity - the amount of water in the air compared to when saturation occurs ● Dew point - the temperature at which dew forms ● Saturation values ○ Vapor pressure ○ Mixing ratio ○ Dew point ○ Dew point depression ● Subsatured Conditions ○ RH < 100% ○ T > Td (dew point) ● Saturated Conditions ○ RH = 100% ○ T = Td ● Supersaturated Conditions ○ RH > 100% ○ T < Td ● Wet Bulb temperature ○ Temperature at which a wetted surface cools due to evaporation ______________________________________________________________________ ________ Pressure Systems: What makes the air move? ● Pressure gradients ○ In the horizontal, the pressure varies only slightly i.e. only a few millibars over several hundred miles/kilometres ○ Vertical Pressure gradients ■ > 200mb in 2km (balanced by gravity) ○ Horizontal Pressure gradients ■ 24 mb in 3000km ● Cold air contracts → relatively increases surface pressure ● Warm air expands → Relatively decreases surface pressure ● Wind, what causes it to blow - horizontal variations in pressure that create a pressure gradient, which is indicated by a change in pressure over a certain distance ○ Force = mass x acceleration (f=ma). ○ Thus, assuming an object’s mass is constant, an exerted force is directly related to acceleration, which the change in velocity ● WInd (closer the lines = stronger the wind) ○ The pressure gradient force is directed inward, toward the center of a surface low (L) ○ The pressure gradient force is directed outward from the center of a surface high (H) ● How the wind works = coriolis force ○ The CF only occurs on Earth because the Earth is rotating. ○ The CF always acts at right angles to the direction of motion ○ The strength of the CF depends on the speed of the object on which it is acting ○ The strength of the CF also depends on the latitude. It is equal to 0 at the equator and is max at the poles. ● The CF is an apparent force, it only applies because we are on something that is rotating ● Throwing a ball to the east → centrifugal force, perpendicular to the axis that the Earth rotates on ● Geostrophic winds - PGF = CF ● Friction with the surface slows the wind speed down. ○ Slower wind speeds reduce the magnitude of the CF; thus the deflection of air parcels to their right is reduced ● L is counter clockwise and inward at the surface ● H is going clockwise and is moving outward from the surface ○ L and H are like this only in the Northern Hemisphere ○ Ageostrophic component is the divergence of wind at the centers of low and high pressure systems. ● The tropopause are where wind speeds are highest Chapters 8 & 9 → Fronts and Stability ● Clouds form as air rises and cools ○ A rising parcel of air expands and cools, whereas a descending parcel of air compresses and warms ○ As the air molecules rises it gets slower/larger and cools ○ When is sinks the speed of the molecules increase and create warmth ● An Adiabatic process → when air parcel/blob rises expands, and cool without exchanging heat or mass with the surrounding environment ● The adiabatic rate of cooling is constant (10C per km) is the dry adiabatic lapse rate ● The moist adiabatic lapse rate is when a cloud creates condensation that causes the environment to warm almost always less than the dry rate of 10C per km ● Atmospheric stability ○ The concepts of air parcels and adiabatic lapse rates are crucial for understanding stability in the atmosphere ○ A Stable Equilibrium is a state in which the perturbed object will return to its original location ○ An unstable equilibrium is the state in which a perturbed object will continue to move away from its original position ○ Conditional instability results when an object may be either stable or unstable, depending on the applied forces ● Atmospheric stability can be determined by comparing the density of an air parcel with that of the surrounding air at the same pressure level ● Parcels that are more dense than their surroundings will sink, whereas those that are less dense will rise (think about placing a beach ball in a pool versus a bowling ball) ● Ideal gas law → relates pressure, density, temperature ○ P (the density) = pressure / (2.87*T) ○ Warmer air parcels are less dense and tend to rise ○ Colder parcels are more dense and tend to sink ● The Environmental Lapse Rate we can compare this to the temperature of a parcel with the temperature of the surrounding environment too ● There are triggers that get the air moving out of its current equilibrium ○ How air gets initially pushed/aggravated ■ Gradients in temperature ■ Large scale convergence ■ Topography (if air goes into a mountain, it goes up) ■ Fronts ● When the temperature and dew point are the same, clouds start to form ● The air stops rising when it hits the equilibrium because it is the tropopause ● Local scale - convergence often occurs in callewys when air currents flow together (tens of miles) ● Intermediate-scale - convergence occurs at the center of cyclonic systems, air flow from high to low pressures (hundreds of miles) ● Air masses ○ an air mass is a large body of air that has fairly similar temperature and humidity in the horizontal ○ As air masses move they carry with them their temperature and moisture ○ Source regions ■ Where air masses tend to form ■ They tend to be flatter areas with uniform composition with light surface winds ○ Origin Location terms: polar (cold), tropical (warm/hot), arctic (very cold) (temperature based) ○ Land (continental) dry , water (maritime) moist (moisture based) ■ 6 different pairings ● cA, cP, cT, mP, mT ● There is no mA because of the moisture/ice already present ○ Continental Polar and Arctic ■ Originate over the ice and snow covered regions of the Arctic, northern canada and alaska ■ Lack of clouds allows temperatures to plummet ■ Surface air is typically stable ■ Little moisture flux, making air very dry ■ Upper-level winds help move this air into the US from time to time ■ Can create: obstructions, lake-effect snow, can cause crop damage in the deep south ■ Strong feature: the air tends to sink with high pressures and creates a subsidence inversion (the temperature increases with height) ○ Surface evap and longer days mean that these air masses are warmer and wetter in the summer ○ mP air tends to less cold then C counterparts and is usually conditionally unstable ■ When reaching the west coast, often brings rain to lower elevations and snow to higher places, removing a large amount of its moisture ○ Backdoor cold front → when the western air moves back into the NE, mixed precipitation ○ Maritime Tropical ■ Originate in the subtropical east Pacific ■ Very warm and moist air that gets slammed into the sierras and extreme rainfall and snowfall can be caused ■ When this mT air comes into the coast it is sometimes called the pineapple express ■ ● Continetal tropical ○ The only source region in North America is northern Mexico and the desert southwest of the US ■ The air is so dry that rising air parcels would not begin condensing until about 10,000 ft above the surface ● Fronts ○ A front is a transition zone between two air masses of different densities ○ Air masses extend in both horizontal and vertical directions; thus, fronts extend upward creating a frontal surface ○ A stationary front has essentially no movement ■ Surface winds tend to blow parallel to the front but in opposite directions ○ When a front starts to move you can tell it will become a cold front or a warm front based on the little triangles that tell us which way the front will move ○ When reading a front map ■ The little circles mean cloud cover ■ The music note like things show where the wind is coming front, and the number of feathers tells us how strong the wind is ■ The two numbers are temperature, and dew point (bottom) ■ The other number (in 1000s means pressure) ■ The two dots mean rainfall two ** mean moderate snow ■ Checkmark below the pressure shows that it is decreasing or increasing ○ As a front dissipates, we know it is doing so because the temperature drops this is called frontolysis ○ In the formation of a temperature gradient and a front is called frontogenesis. ● Warm fronts are typically associated with lighter precipitation ● Occluded front → (purple line on maps) the symbols point in the direction that the front is headed ● Two types of occluded fronts (cold and warm) ○ A cold occlusion is when the cold front is colder than the air of the war front ○ A warm occlusion is when the air behind the cold front is warmer than the air ahead of the warm front ● Dry lines → represent a narrow boundary with a large moisture gradient separating moist and dry air masses ○ Are most common in Texas, can often result in severe weather (tornados) ○ Cold front will have warm temps ahead, and cold behind it ○ Warm front will have cold temps ahead, and warm behind it