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Weather, Wind and Scent Transport And the effect this has on searching 10/17/03 Jeff Orrock, NWS C. Louis, WCSAR 1 What causes air movement.. What creates the air movements Temperature differences Pressure differences Atmospheric stability Prevailing, general winds Topography Scent ‘pooling’ Scent plume patterns 2 What causes the air to move? Differences in air pressure!! – High pressure: clear skies. Air moves clockwise and downward and is warmed with high pressure. – Low pressure: clouds and precipitation. Air moves counterclockwise, upward, and is cooled around low pressure. Prevailing winds (Jet Stream) 3 Temperature, Pressure and Winds The temperature differences cause pressure differences in the atmosphere. Wind blows in an attempt to equalize temperature differences and to balance the pressure differences between denser and lighter air. This creates winds that blow from areas with higher pressure to those with lower pressure. When pressure changes rapidly between two areas, we say that there is a "tight pressure gradient." The tighter the pressure gradient, the stronger the. 4 Highs and Lows Lines around the highs and lows, called "isobars," connect pressure observations that are the same. Lows Center of pressure surrounded on all sides by higher pressure Highs Center of pressure surrounded on all sides by lower pressure Air moves counterclockwise (cyclonically) around the center Air moves clockwise (anticyclonically) around the center Area of rising air Often produces cloudy skies and precipitation Area of sinking air Often suppresses clouds and precipitation 5 Pressure Differences Create Wind Higher pressure pushes air toward lower pressure A half pound per square inch pressure difference between places 500 miles apart will accelerate still air to an 80 mph wind In three hours. Increase the distance to 1000 mile, and the wind would be only 40 mph after three hours. These speeds don’t factor in the effects of friction and other forces. 6 Copyright 1992, USA TODAY. Reprinted with permission. Jet streams Major influences in regional weather Moves from West to East starting at the northwest of the continent, swooping southerly, then a northerly swoop towards the northeast of the continent. 7 Jet Stream - Positions Summer In summer, jet stream weakens and is farther north Winter In winter, with greater temperature contrasts, jet streams are stronger and farther south 8 Copyright 1992, USA TODAY. Reprinted with permission. Jet Stream - Wind Speeds more than 170 mph 150 mph to 170 mph 125 mph to 150 mph 100 mph to 125 mph 80 mph to 100 mph The greater the temperature contrasts, the stronger the pressure differences between warm and cold air. Stronger pressure differences create stronger winds. 9 Copyright 1992, USA TODAY. Reprinted with permission. Upper Air Patterns 1 Air streams converging. 4 4 Air streams diverging. 1 2 3 Air piles up; pressure increasing. High pressure area growing;air flowing out clockwise. 5 Pressure decreasing; air rising 6 Low pressure area growing;air flowing counterclockwise . 10 Copyright 1992, USA TODAY. Reprinted with permission. Cold Fronts The boundaries between different air masses are called fronts. Across a front (which extends vertically as well as horizontally), temperature, humidity, pressure, and/or wind often change rapidly over short distances. •Fast moving with potential of storms •Winds shift from SW to NW or NE A cold front is the leading edge of an advancing cold air mass. At the surface, these fronts mark where cold air overtakes and replaces warmer air. During the spring and summer, cold fronts often initiate thunderstorms and other severe weather. In cold weather, they produce hazardous winter conditions. Because the slope of the cold air mass is steep, temperature, pressure, and weather tend to change dramatically near the front. 11 Warm Fronts •Rain may be a day away (slower moving storms) •Wind shift from SE to SW The edge of an advancing warm air mass is a warm front. At the frontal boundary, warmer air overtakes and replaces colder air. Warm fronts generally bring light or moderate, but steady, precipitation. Notice the slope of the warm air mass is relatively gentle. Consequently, warm fronts are seldom as distinct on the surface as cold fronts, and they usually move much more slowly. 12 Weather Map 13 Localized Weather •Pressure, temperature, and moisture influence weather. On the small local scale, patterns and changes in these variables overlay the larger weather patterns, modifying local weather. •As a result you might have warmer and drier conditions in the open and cooler and more humid conditions in a wooded area with wet ground. •Small-scale changes in pressure, temperature, and moisture can occur for many reasons. Topography plays an important role. Smaller sources of moisture also affect the weather. 14 Atmospheric Stability Lapse rates Concentration/exposure Inversions Humidity Scent plume patterns 15 Lapse rates The amount by which atmospheric temperature decreases over each unit of vertical distance is called the environmental lapse rate. It is a measurement of how rapidly the temperature of the atmosphere decreases with altitude at any particular moment in time. It varies from place to place and time to time. (On the long-term, global average, dry air, it is about 6.5°C per kilometer, or 3.5°F per 1,000 ft.) 16 Lapse Rates Explains also how the atmosphere cools as you rise in altitude. Put very simply: heated air moves faster into a cooler atmosphere If rising air remains warmer than surrounding air, the resulting air is unstable: – The cooling rate is slowed to 3.3 degrees F. with saturated air. – Air is more likely to continue to rise, and with humidity clouds will form. – Puffy cumulous clouds will result, supplying the energy for storms. 17 Lift and Atmospheric Instability An unstable environment is one in which air parcels continue to rise, even after the lifting forces stop. Instability is important because rising air creates vertical cloud development that can result in severe storms. This diagram shows an unstable environment. The temperature of an air parcel (orange balloon) starts out at the same temperature as its surroundings (white line). As it rises, the parcel cools (yellow line). In this case, the environment at 10,000 ft is only 20°F compared to the parcel's temperature of 23°F (temperatures and heights are chosen only as an example). Because it is warmer than its environment, the parcel will continue to rise until it is no longer warmer (at 20,000 ft in this case). Before a mission: check forecast air stability or instability. 18 Lift and Atmospheric Stability In a stable environment, air parcels that are forced upward are colder than their surroundings and tend to sink or spread out. Because the air resists being moved upward, few clouds may form, and those that do will be more horizontal than the one shown in the unstable case. In the example to the right, a parcel lifted to either 10,000 ft or 20,000 ft would be colder than the surroundings, and would not rise further. The temperature inversion is a layer of warmer air on top of colder air. Inversions inhibit vertical motions because, a parcel that reaches the inversion layer is cooling while the environment is warming. Inversions are key factors in air pollution and fog events because they act like lids, trapping air. They are common early in the day, but if the atmosphere heats up enough, the inversion can be destroyed and the fog (scent) will dissipate and disperse. 19 Stable & Unstable Air Altitude Temperature of surrounding air Stable air Unstable air 20 Copyright 1992, USA TODAY. Reprinted with permission. Concentration/exposure Wind inversely proportional to concentration: •stronger the wind, lower the concentration •weaker the wind, higher the concentration The NWS can help with two important variables critical for concentrations/exposure to help gauge ideal SAR condition: Wind & Stability 21 Stability – the downwind plume from an event will be extremely dependent on the structure of the temperature profile in the vertical (the stability) Stable atmosphere stays very confined In the vertical Unstable atmosphere over stable stays confined above surface, but expands aloft 22 Unstable atmosphere spreads vertically with time and distance Very unstable atmosphere spreads very widely over the vertical Stable atmosphere over unstable Starts with little vertical Extent, but with mixing Expands greatly 23 Lifting Mechanisms (thermals) As the sun heats the earth’s surface, parcels of air rise like bubbles. These are called “thermals”. As the air rises and cools, it can produce clouds if it becomes saturated. As the sun heats the land, thermals rise, lowering the pressure. The air over the water is colder and denser, and therefore is an area of relatively higher pressure. As the air from the higher pressure flows toward the lower pressure, it converges and rises. 24 Sea Breeze Land heats up more quickly than water Cold air begins to push inland creating a breeze off the ocean Rising warm air cools and moves over the ocean to replace cold air that moved inland 25 Copyright 1992, USA TODAY. Reprinted with permission. Stable or Unstable?? Stable Clouds horizontal, no vertical motion Stratus clouds Hazy or foggy Steady winds Unstable Clouds are vertical, cumulus Flagging tape goes ‘up’ and ‘down’ (upward and downward currents) Gusty winds Great visibility Leaves spin in circles 26 Inversions Happens when cold air underlies warmer air at higher altitudes, causing stable air. Temperature inversion may occur during the passage of a cold front or result from the invasion of sea air by a cooler onshore breeze. Overnight radiating cooling of surface air often results in a nocturnal temperature inversion which dissipates after sunrise by the warming of air near the ground. You will feel the temperature difference as you move uphill An inversion breaks up after sunrise, and your winds will be crazy 27 Nighttime Inversion (will usually mix out with daytime heating) 28 Humidity (Daily Fluctuation) 29 The Explosive Nature of Water... P Water is the only thing on earth that exists in all 3 phases... Solid - Liquid - Gas P Breaking the liquid bonds (vaporization) requires kinetic energy (heat) which is lost from the environment (ocean)...the ocean cools! P When water vapor condenses, those liquid bonds reform and heat is released to the environment (air), where it exhausts upward. Liquid Water -each water molecule grips and releases its neighbors 6,000,000,000 times per second Like little Magnets 30 Factors affecting wind strength Friction: an object causes the wind to slow (e.g. a ‘catch’) Pressure Gradient force: the pressure difference and the distance between high pressure areas and low pressure areas. 31 32 Topographic effects on winds Slope and Valley winds – Typically uphill/upslope/upvalley winds during day, downhill/slope/valley winds at night. – Up-valley winds begin late morning or early afternoon, ending in the afternoon – Down-valley winds begin gradually, ending with a pooling of cool, heavy air in valley bottoms. Search UP in the morning, DOWN at night 33 This slope aspect Affects humidity levels Affects vegetation Affects wind speed transition times of slope winds. Wind direction shadows sun 34 In Hilly Terrain With morning heating air rising up all slopes will influence the wind speed you experience based on your location to the prevailing wind and exposure Where do you put your K9s team in this example? 35 Terrain Effect Terrain can greatly influence wind direction as well as speed. Wind channels in valleys and low lying areas. This produces a wind direction which will vary significantly than the observed wind measured over the larger area. In the case below the general NE winds are being influenced by the terrain. Those searching the low terrain are experiencing more of a N wind than those elsewhere. Place your K9 teams at night and then at 10am the following morning. 36 Wind Flow and Terrain 37 Wind Shadow behind Tree Line 38 Combination of Terrain and Stability on Wind Flow 39 Terrain and Heating As discussed before heating over different terrain will cause a thermal imbalance thus generating wind. In this example the wind is being influenced by a large Or other body of water. The same holds true for wooded versus open areas. Place your K9’s at in each example 40 Less Friction Over Water Enhanced winds on downwind (lee) side of the lake. 41 Picture: scent plume patterns looping Fanning lofting Fumigating Evening Sunrise Search lower areas Daytime Sundown Search ridges 42 Clear weather scent plume patterns Looping –occurs in a high degree of convective turbulence Coning – ideal scenting conditions Fanning – scent cone compression vertically and spreads horizontally, usually caused by an inversion 43 Clear weather scent plume patterns Fumigating – stable air is above, unstable air at the surface, allowing cooler air to diffuse down through to the ground at daybreak. This happens at sunrise in lower areas… Think of fishing on a lake with the funny vertical ‘lake fog’. Search lower areas Lofting: think of this as the opposite of fumigating. Happens after sunset on ridges. Occurs after the sun sets and the ground is cooling. Try searching ridges and higher slopes. This happens when you have stable air at the surface, and unstable air on the ridges. 44 Scent Pooling Occurs in Heavy brush: wax myrtles Porous rocks Depressions Moist areas Pool of scent 45 Pooling of cold air Cold air is heavier and more dense than warm air. On very calm days in the woods and especially on calm nights colder air will settle into low lying areas. This results in higher humidity values in low areas. Where do you put your K9 team? 46 What might your K9 do upon reaching this mossy tree area if the victim was located up the hill? 47 What clues tell you when your dog has or has lost scent? Dog’s tail suddenly down, ears suddenly back (whatever is ‘not’ your dogs normal search behavior!) Dog looks at you Dog stops moving, or blocks your path Dog sits Dog whines, clearly frustrated Dog ‘heals’ Dog has more interest in food/water/critters It is our job to determine why!! 48 Why does the dog lose the alert? You have gone past the subject (Is the wind at your back now? Could your dog be interested in a ‘catch’ vs a subject?) Wind currents have changed due to topography Wind currents have changed due to weather changing Wind currents changed due to obstruction 49 Obstructions Eddies: In heavy trees, wind is forced up over the trees creating turbulence which eddy on the leeward side of the trees. Obstacles: Depending on spacing between obstacles you create gaps where the dog can’t detect scent. Drainages: Wind velocity and size of dropoffs create scent ‘gaps’ 50 Chimney effect Beginner problem #1: Run into the trees and hide. The victim sits next to a warm tree on a sunny day. Problem: On hot days, trees heat up so scent rises straight up into the air rather than being carried by predominant winds. Results: your dog blows past the subject. Don’t fret: tell your victim to sit in the Shade! 51 POD for dogs based on Air Stability POD including factors such as Wind surface speed Stability of air – Clear or cloud cover – day or night searching For an example of this see POD based on Graham, Hatch’s Probability of detection for air-scenting dogs in wilderness searches 52 So what creates the weather in my search area? The relationships among pressure, temperature, moisture, topography, stability, and lifting mechanisms are very complex, and they are further complicated by the interactions on all the scales we have discussed. It is difficult to make generalizations. The best advice is to understand the basics of meteorology and the Current and forecast conditions for your search area. * Check the weather and then talk to your NWS office about conditions which might trouble you 53 http://weather.gov/raleigh Watch, Warning and Advisory display. Shows current products in effect. Click on your LOCATION of interest for best one stop shopping! (This provides you a POINT forecast…ie. Durham) 54 Point Forecast is generated off a 5 km grid providing you are forecast for more of a specific location versus a large area forecast. Hourly graphs of weather conditions through 48 hours. 55 Detailed Forecast provides weather type and timing Useful for timing of adverse weather as well as a first guess for HAZMAT, SAR and other operations. 56 How to get current Conditions? 57 58 59