INTRODUCTION TO METEOROLOGY PART ONE SC 213 MAY 21, 2014 JOHN BUSH

WEATHER PATTERNS Extratropical cyclones (low pressure core) and anticyclones (high pressure core) Cold fronts and warm fronts Jet stream (jet streaks)

WARM AND COLD FRONTS

May 18 May 18

May 18 May 20

May 18 May 21

Current conditions in Minneapolis

STATION MODEL WHAT DO YOU NEED TO KNOW TO TRACK WEATHER? Wind speed & direction Dry bulb & dewpoint temperatures Present weather & visibility Low-altitude cloud type & height of cloud base Part of sky covered by low-altitude clouds High- & mid-altitude cloud types Barometric pressure at sea level Amount & direction of pressure tendency in past 3 hours Weather and amount of precipitation in past 6 hours

STATION MODEL

SOME THINGS YOU MAY ALREADY KNOW DENSITY Buoyancy lower density air rises -Positive: air rises -Negative: air sinks Warm/moist air has lower density Fluids of different densities resist mixing The gas law relates the pressure, volume(density) and temperature of air: -Pressure is proportional to temperature divided by volume -Density is proportional to pressure divided by temperature

SOME MORE THINGS YOU MAY ALREADY KNOW TRANSFERRING HEAT Convection is the transfer of heat or moisture by currents of air Convection is the most efficient way to transfer heat: natural, forced Winds: pressure gradient force propels air Winds can force convection Adiabatic expansion/compression cools/heats air without transferring heat Diabatic heating or cooling transfers heat

SOME FAMILIAR WEATHER FEATURES Land/sea breezes Santa Ana winds

MORE THINGS YOU MAY ALREADY KNOW TEMPERATURE OF THE ATMOSPHERE The temperature of the standard atmosphere decreases with height in the troposphere The lapse rate measures the rate of change of air temperature with altitude There are several important lapse rates: ELR, DALR, MALR At the tropopause the environmental lapse rate changes sign

DEFINED STANDARD ATMOSPHERE TEMPERATURE VERSUS ALTITUDE

DEFINED STANDARD ATMOSPHERE PRESSURE VERSUS ALTITUDE

SOME MORE THINGS YOU MAY ALREADY KNOW WATER IN THE ATMOSPHERE The water content of saturated air (vapor capacity) is very sensitive to temperature: approximately doubles each 10 C increase in temperature When water changes phase, heat is released (condensing, freezing) or absorbed (evaporating, melting) Latent heat Above -40 C the formation of ice crystals or water droplets requires nuclei --supercooling

MORE ABOUT WATER IN THE ATMOSPHERE Saturated air: When vapor capacity and vapor supply are equal air is saturated Relative humidity is 100% Dry Bulb temperature, dewpoint temperature and wet bulb temperature are equal Subsaturated air: Vapor supply is less thn vapor capacity

BRINGING SUBSATURATED AIR TO SATURATION Decrease vapor capacity by decreasing temperature: Adiabatic cooling Isobaric cooling--dewpoint Increase vapor supply from an external source Increase vapor supply and decrease vapor capacity by decreasing temperature temperature : wet bulb approach

LECTURE 8: CONCLUSIONS BRINGING AIR TO SATURATION

INTRODUCTION TO CLOUDS WHY ARE CLOUDS INTERESTING? Indicators of future weather Indicators of dynamic processes in the atmosphere Interesting to pilots (and passengers) Interesting esthetics

CLOUD SHAPES Most common Horizontal layers (stratiform) Vertical heaps (cumuliform) Many others

SOME UNCOMMON TYPES

COMMON TYPES High clouds cirrus above 20,000 ft Cirrus Mid level clouds-alto 7000-20.000 ft Low clouds Below 8.000 ft Fog Stratocumulus Stratus Nimbostratus Vertical clouds Cumulus up to 20,000 ft Cumulonimbus up to 75,000 ft Altocumulus Nimbostratus Cumulonimbus

LECTURE NINE CLOUDS, STABILITY, AND BUOYANCY: PART 1

LECTURE TEN CLOUDS, STABILITY, AND BUOYANCY: PART 2 LCL: Lifting condensation level (cloud base) LFC: Level of free convection EQL: Equilibrium level (cloud top) CIN: Convective inhibition CAPE: Convective available potential energy

LECTURE TEN CLOUDS, STABILITY, AND BUOYANCY PART 2 Sea breeze front Formation of thunderstorms

PASSAGE OF A SEA BREEZE FRONT LAGUNA BEACH LAGUNA HILLS MAY 20, 2014

Next Week: Whence and Whither the Wind?

MAY GRAY JUNE GLOOM