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Joe Solomon National Weather Service Pendleton [email protected] 541-276-8134 Nighttime Temperature profile of an Inversion A Layer of Warm air over Cold air Inversions Cold air is more dense and heavier than warm air Profile of the Atmosphere -60 -20 20 60 100 140 Temperature normally decreases with increasing altitude in the troposphere. 140 Temperature THERMOSPHERE/ IONOSPHERE 100 60 Pressure 60 Mesopause MESOSPHERE Stratopause 20 -20 20 60 100 40 Referred to as Lapse Rate. STRATOSPHERE cooling 20 Tropopause -60 80 TROPOSPHERE 140 02-05-S290 Comparing Lapse Rate & Stability LAPSE RATE 3.5 degs. / 1000 ft. (Average) 5.5 degs. / 1000 ft. (Dry) Change in Temperature 3.0 degs. / 1000 ft. (Moist) Neutral <5.5 degs. / 1000 ft. (STABLE) With Altitude 1,000 ft. >5.5 degs. / 1000 ft. (UNSTABLE) Temperature 04-06-S290 Lapse Rate = rate at which temperature changes with height 1 S-290 Skills…Atmospheric Stability Air Stability Stable Air – Resists vertical motion Poor Ventilation/Mixing Height Unstable Air – Encourages vertical motion 04-11-S290 Good Ventilation/Mixing Height A Day in the Life of a Rising Air Parcel 8.0º 8.0º F 49.0º 49.0º F 8.5º 8.5º F A Day in the Life of a Rising Air Parcel 13,000 ft AGL 55.0º 55.0º F 52.5º 52.5º F 5,000 ft AGL 52.5º 52.5º F A parcel of air will continue to rise as long as it remains warmer than the air around it. 74.0º 74.0º F 0 ft AGL 80.0º 80.0º F bare field Fields covered with vegetation 06-53-S290-EP 5,000 ft AGL Once the parcel becomes cooler than the air around it, it stops rising. If it becomes cooler than the air around it, it begins to sink. 74.0º 74.0º F 0 ft AGL 80.0º 80.0º F bare field Fields covered with vegetation 06-53-S290-EP A Day in the Life of a Rising Air Parcel If the parcel never becomes warmer than the air around it, it never rises. 74.0º 74.0º F 73.0º 73.0º F bare field 0 ft AGL Fields covered with vegetation 06-53-S290-EP The skew-T diagram is used to represent the pressure, temperature, density, moisture, wind and atmospheric stability within a column of atmosphere above a point on the earth’s surface. 2 Spokane Morning Sounding Temperature normally decreases with increasing altitude… But what is normal when it comes to weather? cooling What is a Temperatures Inversion? Atmospheric Lapse Rates An inversion is a layer of very stable air where temperature increases with an increase in altitude. Very Stable 15º F/M FT An inversion acts like a cap or lid to severely limit the upward movement of air. -3º F/M FT -5.5º F/M FT Warmer Inversions often exist at many levels of the troposphere. Unstable Stable Neutral -15º F/M FT Temperature Polar Region Troposphere 04-12-S290 The Troposphere The lowest layer of the atmosphere varies in height from 9 to 12 miles above sea level over the tropics, to about 6 miles above sea level over the polar regions. The Tropics 3 The Solar Radiation Budget Reflected by earth’s surface: 3% Reflected by clouds: 22% Reflected by atmosphere: 5% 100% 5% Direct Sunlight Heat Loss at Night Net Radiation to Space and Atmosphere Absorbed by atmosphere and clouds: 20% 22% Absorption by Clouds and Atmosphere Direct 50% 3% Reflection from Clouds Convection and Conduction from Air near surface Condensation of Dew Indirect Sunlight Conduction from Soil Faster cooling near the surface than aloft 02-10-S290 02-20-S290 The Seasons in the Northern Hemisphere Seasonal Change In Solar Angle At 40ºN Latitude The Solar Radiation Budget Angle of Solar Rays Reflected by earth’s surface: 3% Reflected by clouds: 22% Reflected by atmosphere: 5% 100% 5% > 15% Direct Sunlight N Absorbed by atmosphere and clouds: 20% 22% > 35% Direct S 3% > 10% 50% > 20% Indirect Sunlight 02-27-S290 02-10-S290 4 (Seasonal) Net Incoming vs. Net Outgoing Radiation Incoming Radiation Outgoing Radiation Seasonal warmest Temperature • The end result…the impact of inversions is greater during the Winter VS Summer as Winter inversions can last many days. Seasonal coldest Temperature Amount of Heat Mar Jun Sep Dec 02-29-S290 Nighttime or Radiation Inversion Four Types of Inversions Sunset Strong cold air drainage Weak inversion Midnight Weak cold air drainage Moderate Inversion Sunrise Little or no drainage flow Strong Inversion During the evening hours, this surface based inversion is weak and shallow, usually no more than a few hundred feet deep. As cold air drainage and radiational cooling continues overnight, this inversion strengthens and eventually reaches its maximum depth around sunrise when surface temperatures are at their lowest. Drainage winds Summer Nights Shallow Inversions Winter Nights Deep Inversions lower on valley walls and mountain slopes during the summer with shorter nights and less radiational cooling and cold air drainage. higher on winter nights with stronger radiational cooling and cold air drainage. May be thousands of feet above the valley floor. 5 Thermal belts tend to form higher on the walls of broad valleys and gently slopes canyons. Broad Valleys lower on mountain slopes and steep canyons with strong drainage. Most Effective Way to Destabilize (Change slope of temperature line ~ increase lapse rate) 5.5 degs. / 1000 ft. (Dry) Cooling Aloft (Upper level “disturbance”) Resulting lapse rate 1,000 ft. Surface Heating (Sunshine) Temperature Evolution of the Mixing Layer. Summer Comparing Lapse Rate & Stability 3.5 degs. / 1000 ft. (Average) 5.5 degs. / 1000 ft. (Dry) 12,000 Ft AGL 3.0 degs. / 1000 ft. (Moist) Maximum Mixing Height 2 PM 7400 Ft AGL Neutral <5.5 degs. / 1000 ft. (STABLE) 1,000 ft. 2 PM Noon Noon 10 AM 10Ft AM 1500 AGL >5.5 degs. / 1000 ft. (UNSTABLE) 2800 FT AGL 58ºF 8 AM 8 AM Temperature Lapse Rate = rate at which temperature changes with height 55ºF 63ºF 75ºF 80ºF 88ºF Evolution of the Mixing Layer. Spring or Fall Maximum Mixing Height 2 PM 10 AM 50ºF 45ºF 53ºF 58ºF 2000 FT AGL 1500 Ft AGL 2 PM 10 AM Ground Ground Evolution of the Mixing Layer. Winter 500 Ft AGL 50ºFHeight Maximum Mixing 45ºF 53ºF 2 PM 2 PM 58ºF Ground 6 Inversions break as temperatures near the surface increase fasten than aloft. Common during the Summer, but more difficult to occur during the Winter due to lack of surface heating. Inversion form by temperatures cooling near the surface fasten than aloft. 5000’ Height Dry Adiabat 2000 0500 0200 1830 0 Temperature Four Types of Inversions Subsidence Inversions Aloft Subsidence Subsidence Inversions Inversions Aloft strongest in late summer and autumn, and on the north and east sides of strong high pressure ridges that remain over a region, sometimes for weeks at a time. Lowering Subsidence Inversion Temperature Sounding Subsidence is a slow process that can occur over several days. During this period, a subsidence inversion will grow stronger as it lowers and becomes progressively warmer and drier than the layer of air below it. Poor ventilation conditions develop below a lowering subsidence inversion. 7 Cold Fronts Cold Fronts Fronts with with Cold Wind Wind 05-31-S290 05-32-S290 Frontal Passage warmer, lighter air cooler, heavier air 8