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Credits www.epa.gov/airnow/2004conference/.../ne se_meteorology_101.ppt Meteorology 101. Fundamentals of Weather. Jon Nese and Jen Carfagno. The Weather Channel. February 22, 2004. Meteorology 101 Questions to Answer • How, why, when, where does the wind blow? • What controls vertical motions? • When and where do clouds and precipitation form? What are two differences between a warm and cold front? What are two differences between a Low Pressure System and a High Pressure System? Meteorology 101 Geographical Terminology… Meteorology 101 Layering of the Atmosphere Stratosphere 6-8 Altitude (mi) Troposphere Temperature Planetary Boundary Layer 78.09% nitrogen 20.95% oxygen 0.93% argon 0.039% carbon dioxide Small traces of other gases Variable amounts up to 1% of water vapor Troposphere—lowest layer (upper boundary called tropopause) Temperature decreases with altitude Rate of cooling is variable but averages about 6.5ºC per km Stops decreasing at tropopause—9km at poles and 16km at the equator Contains the most water vapor Contains about 80% of the mass of the atmosphere Jet stream is located just under tropopause All Earth’s weather occurs here. High-Level Clouds (Cirrus) High-level clouds form above 20,000 feet (6,000 meters) and since the temperatures are so cold at such high elevations, these clouds are primarily composed of ice crystals. High-level clouds are typically thin and white in appearance, but can appear in a magnificent array of colors when the sun is low on the horizon Mid-Level Clouds The bases of mid-level clouds typically appear between 6,500 to 20,000 feet (2,000 to 6,000 meters). Because of their lower altitudes, they are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are cold enough. Low-level Clouds Low clouds are of mostly composed of water droplets since their bases generally lie below 6,500 feet (2,000 meters). However, when temperatures are cold enough, these clouds may also contain ice particles and snow. Vertically Developed Clouds Probably the most familiar of the classified clouds is the cumulus cloud. Generated most commonly through either thermal convection or frontal lifting, these clouds can grow to heights in excess of 39,000 feet (12,000 meters), releasing incredible amounts of energy through the condensation of water vapor within the cloud itself. Vertically Developed Clouds Fair Weather Cumulus Vertically Developed Clouds Cumulonimbus clouds (Cb) are much larger and more vertically developed than fair weather cumulus. They can exist as individual towers or form a line of towers called a squall line. Fueled by vigorous convective updrafts (sometimes in excess 50 knots), the tops of cumulonimbus clouds can easily reach 39,000 feet (12,000 meters) or higher. Orographic Clouds forced by the earth's topography Orographic clouds are clouds that develop in response to the forced lifting of air by the earth's topography (mountains for example). •Exosphere Outer •Thermosphere Mid •Mesosphere •Stratosphere Low •Troposphere •Earth Stratosphere—second layer (upper boundary called stratopause) Clear, dry layer 50km above the Earth’s surface Lower part is about as cold as tropopause Warms steadily to stratopause Warming due to ozone Ozone absorbs uv rays and releases some as heat How do we reduce damage to the ozone layer? Mesosphere—third layer (upper boundary called mesopause) 50km to 90km above the Earth’s surface Temperature drops with altitude Layer where meteors burn up Noctilucent clouds form here Thermosphere—outermost layer Temperature rises with altitude Temperatures can rise above 1000ºC Extremely thin; few molecules Highest layers—composed of lighter gases (He, H2) Lowest layers—composed of heavier gases(N2,O2) Contains the ionosphere Located between 90 and 500km Air is highly ionized due to the uv rays Affected by solar events Can disrupt radio transmissions Form auroras Thermosphere (con’t) Contains the ionosphere Located between 90 and 500km Air is highly ionized due to the uv rays Affected by solar events Can disrupt radio transmissions Form auroras Meteorology 101 Some Fundamentals • Earth is heated unevenly: Tropics are warmer than the Polar Regions. • Nature tries to try to even out temperature differences. • Uneven heating sets atmosphere in motion and is the fundamental cause of all weather. Meteorology 101 Radiation is the transfer of thermal energy by electromagnetic waves Meteorology 101 Convection is the transfer of energy by the movement of heated material from one place to another. Conduction is the transfer of energy between objects when their molecules collide Meteorology 101: What is this? Warm Air Mass? Cold Air Mass? Moist Air Mass? Meteorology 101: What is this? A Cold Front Meeting a Warm Air Mass. When cold air contacts warm air??? Warm air rises into cooler atmosphere Condensation occurs (Rain) Meteorology 101: What is this? Cumulonimbus Supercell Thunderstorm Meteorology 101: What is this? Lake Effect Snow Warm water evaporates. The warm water moves over land The land is cooler. Precipitation occurs (condensation) Meteorology 101 Isobars (like a topographic map of atmospheric pressure) Millibars (like pounds of pressure) How would you describe the change in atmospheric pressure along the orange arrow? Meteorology 101 How many times more dense is the troposphere than the thermosphere? Meteorology 101 The Coriolis Effect Meteorology 101 The Coreolis Effect Meteorology 101 Meteorology 101 Air Pressure “Top” On average, air weighs about 14.7 lb/in2 14.7 lb/in2 =29.92 “inches of mercury” 1” 1” Air Pressure varies over the globe Meteorology 101 Changing Pressure - Winds Take more out than put in – decrease pressure Put more in than take out – increase pressure Meteorology 101 Changing Pressure - Temperature Cold Warm Coldest column = highest pressure ** Warmest column = lowest pressure ** Meteorology 101 Pressure Differences Create Wind Air moves from higher toward lower pressure Meteorology 101 Vertical motions also occur Air “converges” at lows, and rises. Air “diverges” at highs, and sinks. Meteorology 101 Reality is more complicated Actual winds around highs and lows Meteorology 101 Rising Air near ows • Rising air cools; water vapor in the air condenses to form clouds/precipitation • Lows tend to bring cloudy, wet weather Sinking air near ighs • Sinking air warms and dries out. • Highs tend to bring fair, dry weather. Meteorology 101 Low or lowering pressure = “Lousy” weather Meteorology 101 Cold Warm General Circulation Meteorology 101 Cold Warm Front = Battleground of Air Masses • Temperature differences concentrated • Zone of lower pressure where lows (storms) often form Meteorology 101 Cold Front Colder Warmer Colder Warmer Cold air advances Warm Front Warm air advances* Colder Warmer Stationary Front Meteorology 101 What happens when air masses meet at fronts? Cold Warm Cold air lifts the warmer air. Clouds and precipitation form. Meteorology 101 Ridge UpperLevel Features Trough Westerlies - High-Altitude winds blow generally west-to-east 3-6 miles above midlatitudes. Jet Stream – River of fastest-moving air within the westerlies. Meteorology 101 Reality is messier … Still, highs and Lows move with the westerlies and the jet stream. Meteorology 101 RIDGE SINKING AIR HIGH PRESSURE FAVORED TROUGH RISING AIR LOW PRESSURE FAVORED Highs and Lows form and dissipate in synch with ridges and troughs in the westerlies. Meteorology 101 LOW This is your life! COLD WARM Stationary Front separates air masses Meteorology 101 LOW This is your life! COLD WARM Area of low pressure develops along front Meteorology 101 LOW This is your life! Circulation around low sends cold air and warm air advancing Meteorology 101 COLD LOW This is your life! COLD WARM Low and fronts move with the upper-air westerlies while circulating low-level air Meteorology 101 LOW This is your life! Cloud Shield Precipitation Shield Warm Sector Typical cloud and precipitation shield of a low-pressure system and fronts Meteorology 101 Intense lows often take on a “comma-cloud” shape when viewed from space. Meteorology 101 Local Winds Warm Sea Breeze Land Heats faster Water Uneven heating working on a smaller scale