ATMO 336 1st Edition Lecture 15Outline of Last Lecture II. Rising air cools and expands as It risesIII. Conditions for cloud formation (forcing air to rise) 4 basic conditionsa. Surface heating and free convectionb. Horizontal convergence of surface air and/or horizontal divergence of air at top of tropospherec. Topography (mountains)d. Uplift along weather frontsIV. Precipitationa. Collision and coalescenceb. Bergeron processc. Cloud seedingd. VirgaV. Types of precipitationa. Rainb. Snowc. Freezing rainOutline of Current Lecture VI. Stability of the atmospherea. Stratiform cloudsb. Cumuliform cloudsVII. What makes an atmosphere unstablea. Concept of stabilityVIII. Predicting violent stormsa. Important factors for unstable conditionsIX. Intro to thunderstormsa. 3 ways to make an atmosphere more unstableb. verticle extension into cumuloniumbus cloudc. latent heat necessary for energy of thunderstormX. distribution of thunderstormsa. occur usually in tropicsb. less common over tropical oceansc. most common in middle latitude regions of earth (southeastern US)d. fewest thunderstorms along west coastCurrent LectureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Stability of the atmosphereo Two general types of clouds Stratiform- type clouds- Vertically thin layers of cloud that often cover large horizontal areas- Tend to form in stable environmental conditions Cumuliform-type clouds- Vertically tall clouds, but horizontally not that large, often see clear sky between cloud elements- Tend to form in unstable environmental conditionso Atmosphere does not need to be unstable for clouds and precipitation to occur and most often the atmosphere is stable.o Clouds and precipitation commonly form in stable atmospheric conditions( air is forced upward)- What makes an atmosphere unstableo Only if the temperature of a lifted parcel becomes warmer than surrounding airo Besides mechanism of surface heating and free convection, the only other way in which parcels become unstable is when the latent heat released during cloud formation (water vapor condensing to liquid droplets) is enough to make the temperature of the parcel warmer than the surrounding environmental air.o Concept of stability If parcel temp higher than surrounding air temp, parcel is positively buoyant andwould tend to move upward if released (unstable situation) = less dense than surrounding atmosphere If parcel temp is lower than surrounding air temp. parcel is negatively buoyant and would move downward if released (stable situation)= more dense than surrounding atmosphere Parcel temp equal to surrounding air temp,.parcel is neutral and remain stationary if released. This signals a transition from stable  unstable or unstable  stable- Predicting violent stormso Lift parcels upward to see if they become unstable. This must be done for the current measured atmospheric conditions as well as for forecasted conditions in the futureo The more unstable conditions, the greater potentials for violent storms The depth of unstable layer is important The greater the positive difference between the parcel temperature and the surrounding air temperature, the more unstable the atmosphere- Intro. To thunderstormso Form when moist unstable air is lifted vertically into atmosphere due to unequal heating of the earths surface, oregraphic lifting, dynamical lifting, and/or upper level divergence (frontal zones)o Immediately after lifting begins, rising parcel of warm moist air begins to expand and cool until certain level with saturation = condensation (latent heat released= much of the energy used in thunderstorm development)o Vertical extension of air parcels= cumulus cloud grows into a cumulonimbus cloud (reaches height of 20 kilometers)o Requires unstable atmosphere (more unstable, the more violent the storm. 3 ways to make atmosphere more unstable- 1. Warm air at the surface- 2. cool air aloft (4000-7000 meters- 3. Add more water vapor at the surface (increase dew point temperature of air near ground) this will mean that more latent heat willbe released during cloud formation (parcel becomes warmer than surrounding environment)- distribution of thunderstormso estimated 40,000 thunderstorms occur each day around world (14,500,000 per year)o occur usually in tropics( where intense sunshine heats moist surface all year round)o thunderstorms less common over tropical oceans because ocean surfaces do not warm as rapidly as land surfaces (= much more common over land)o the most common place for sever thunderstorms is in the middle latitude regions of the earth (warm moist tropical air can mix with cold polar air) greatest incidence of thunderstorms occurs in southeastern US ( florida especially due to being surrounded by warm ocean water)o few thunderstorms along west coast= adjacent to cold surface ocean water which makesthe atmosphere stable and not conducive to thunderstorm