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CHAPTER 6

CHAPTER 6. STABLE AND UNSTABLE AIR. HOMEWORK. READ AVIATION WEATHER CHAPTERS 6 & 9 AOPA MOUNTAIN FLYING course due on Tuesday January 24. Statement as of 9:42 PM PST on January 20, 2009.

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CHAPTER 6

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  1. CHAPTER 6 • STABLE AND UNSTABLE AIR

  2. HOMEWORK • READ AVIATION WEATHER CHAPTERS 6 & 9 • AOPA MOUNTAIN FLYING course due on Tuesday January 24

  3. Statement as of 9:42 PM PST on January 20, 2009 • ... Air stagnation advisory remains in effect until 12 PM PSTFriday... An air stagnation advisory remains in effect until 12 PM PSTFriday. Strong high pressure will remain over the inland northwestthrough at least Friday morning. Light winds and a strong lowlevel inversion will contribute to the potential for increasedpollutants in the lower atmosphere.An air stagnation advisory indicates that due to limited movementof an airmass across the advisory area... pollution may increaseto dangerous levels. Persons with respiratory illness shouldfollow their physicians advice for dealing with high levels ofair pollution.

  4. KMWH 192152Z 35010KT 1 1/4SM R32R/5000VP6000FT -SN BKN025 OVC034 M09/M12 A2963 RMK AO2 SLP054 P0001 T10891117 $KMWH 192052Z 35013KT 1SM R32R/4000V5000FT -SN OVC021 M09/M12 A2965 RMK AO2 SLP063 P0002 60004 T10941122 56025KMWH 191952Z 35010KT 3/4SM R32R/3000V4000FT -SN VV018 M09/M13 A2968 RMK AO2 SLP069 P0002 T10941128KMWH 191921Z 35013KT 3/4SM R32R/4000V4500FT -SN VV020 M10/M13 A2969 RMK AO2 P0001KMWH 191852Z 35013KT 1SM R32R/4500VP6000FT -SN OVC024 M10/M13 A2971 RMK AO2 SLP081 P0000 T11001133KMWH 191813Z 35011KT 1 1/2SM R32R/6000VP6000FT -SN BKN026 OVC036 M10/M14 A2973 RMK AO2 P0000KMWH 191752Z 35011KT 1 3/4SM -SN OVC035 M11/M14 A2973 RMK AO2 SNB1656 SLP090 P0000 60000 T11061144 11106 21117 56010KMWH 191749Z 35011KT 1 3/4SM -SN OVC035 M11/M14 A2973 RMK AO2 SNB1656 P0000KMWH 191725Z 36013KT 2 1/2SM R32R/1600VP6000FT -SN OVC035 M11/M14 A2973 RMK AO2 SNB1656 P0000KMWH 191707Z 35012KT 3SM -SN OVC033 M11/M14 A2974 RMK AO2 SNB1656 P0000KMWH 191652Z 35010KT 2SM HZ OVC033 M11/M14 A2974 RMK AO2 UPE1559 SLP094 P0000 T11111144KMWH 191620Z 35009KT 2SM HZ SCT014 OVC031 M11/M15 A2975 RMK AO2 UPE1559 P0000 $KMWH 191617Z 35011KT 2SM HZ BKN014 OVC029 M12/M15 A2975 RMK AO2 UPE1559 P0000 $KMWH 191552Z 35010KT 6SM UP OVC012 M12/M16 A2976 RMK AO2 UPB42 SLP101 P0000 T11171156 $KMWH 191452Z 35010KT 10SM OVC014 M12/M17 A2979 RMK AO2 SLP109 T11171167 56014 $KMWH 191352Z 35010KT 10SM OVC014 M12/M17 A2979 RMK AO2 SLP108 T11171167 $KMWH 191315Z AUTO 35010KT 10SM OVC014 M12/M17 A2981 RMK AO2 $KMWH 191252Z AUTO 35007KT 10SM OVC016 M12/M16 A2981 RMK AO2 SLP115 T11171161 $KMWH 191152Z AUTO 35010KT 10SM OVC022 M11/M16 A2983 RMK AO2 SLP123 70016 T11111161 11100 21111 58006 $KMWH 191052Z AUTO 35006KT 10SM OVC022 M11/M16 A2983 RMK AO2 SLP122 T11111156 $KMWH 190952Z AUTO 35008KT 10SM OVC024 M11/M16 A2985 RMK AO2 SLP128 T11061156 $KMWH 190852Z AUTO 35008KT 10SM OVC024 M11/M15 A2985 RMK AO2 SLP128 T11061150 58001 $KMWH 190808Z AUTO 36009KT 10SM BKN024 OVC033 M10/M14 A2985 RMK AO2 $KMWH 190752Z AUTO 36009KT 10SM FEW028 OVC033 M10/M14 A2986 RMK AO2 SLP132 T11001139 410061106 $KMWH 190652Z AUTO 35004KT 6SM HZ OVC039 M11/M13 A2985 RMK AO2 SLP130 T11061133 $KMWH 190604Z AUTO 33005KT 3SM HZ SCT023 OVC039 M11/M13 A2984 RMK AO2 $KMWH 190552Z AUTO 33005KT 2SM HZ OVC023 M11/M13 A2985 RMK AO2 SLP130 T11061133 11083 21106 51008 $KMWH 190452Z 35007KT 3SM HZ OVC023 M10/M13 A2984 RMK AO2 SLP124 T11001133 $KMWH 190352Z 33008KT 6SM HZ OVC019 M10/M14 A2983 RMK AO2 SLP121 T11001139 $KMWH 190252Z 35005KT 10SM OVC021 M09/M14 A2982 RMK AO2 SLP118 T10941139 51010 $KMWH 190152Z 35007KT 10SM OVC024 M09/M14 A2981 RMK AO2 SLP114 T10891139 $KMWH 190124Z 36007KT 10SM OVC028 M09/M13 A2980 RMK AO2 $KMWH 190052Z 35009KT 10SM OVC035 M09/M13 A2980 RMK AO2 SLP111 T10891133 $KMWH 182352Z 36012KT 10SM FEW035 BKN060 M09/M13 A2979 RMK AO2 SLP106 60005 T10891128 11078 21094 51008 $KMWH 182252Z 35012KT 4SM HZ FEW035 OVC060 M09/M13 A2978 RMK AO2 SNE2155 SLP103 P0000 T10891128 $KMWH 182152Z 35015KT 4SM -SN FEW035 OVC060 M08/M12 A2978 RMK AO2 SNB2053 SLP103 P0000 T10831122 $

  5. KMWH 182052Z 35012KT 4SM HZ FEW035 OVC060 M08/M12 A2977 RMK AO2 SNE33 SLP095 P0000 60005 T10781117 58016 $ KMWH 182025Z 36015KT 4SM -SN FEW034 OVC050 M08/M12 A2978 RMK AO2 P0000 $ KMWH 181952Z 35014KT 1/2SM R32R/2200V4000FT SN BKN014 OVC028 M09/M12 A2979 RMK AO2 TWR VIS 3/4 SLP103 P0003 T10891117 $ KMWH 181930Z 35017KT 1/2SM R32R/2400V2800FT SN VV013 M09/M12 A2979 RMK AO2 TWR VIS 3/4 P0002 $ KMWH 181906Z 35015KT 1/4SM R32R/2000V2600FT +SN VV010 M09/M12 A2981 RMK AO2 TWR VIS 3/4 P0001 $

  6. KMWH 172252Z 24016G21KT 10SM BKN080 OVC090 03/M05 A2973 RMK AO2 SLP078 T00281050 $KMWH 172152Z 25017G23KT 10SM SCT048 BKN065 OVC090 03/M03 A2972 RMK AO2 PK WND 26033/2116 SNB24E34 SLP073 P0000 T00331033 $KMWH 172142Z 24014G21KT 10SM SCT030 BKN070 OVC090 03/M03 A2971 RMK AO2 PK WND 26033/2116 SNB24E34 P0000 $KMWH 172130Z 24018G31KT 4SM -SN BLSN BKN026 BKN048 OVC095 03/M03 A2971 RMK AO2 PK WND 26033/2116 SNB24 P0000 $KMWH 172122Z 25024G33KT 5SM BLSN SCT032 BKN048 OVC070 04/M06 A2971 RMK AO2 PK WND 26033/2116 $KMWH 172052Z 22019G29KT 10SM BKN042 BKN050 OVC070 06/M06 A2970 RMK AO2 PK WND 21030/2017 SLP068 T00561056 58017 $ Decreasing then decreasing more rapidly1.7 hectopascals KMWH 171952Z 23023G30KT8SM FEW025 OVC090 06/M06 A2972 RMK AO2 PK WND 22030/1949 SLP073 T00561056 $KMWH 171852Z 20011KT 10SM CLR 03/M04 A2974 RMK AO2 SLP084 T00281044 $KMWH 171752Z 19013G19KT 10SM CLR 01/M05 A2975 RMK AO2 SLP088 T00111050 10017 21017 56010 $KMWH 171652Z 19012G19KT 10SM CLR 01/M05 A2977 RMK AO2 SLP094 T00061050 $KMWH 171552Z 18009KT 10SM CLR M01/M06 A2977 RMK AO2 SLP092 T10111056KMWH 171452Z 18011G18KT 10SM CLR M01/M07 A2978 RMK AO2 SLP098 T10061067 56022 $KMWH 171352Z 19013G23KT 10SM CLR 00/M07 A2981 RMK AO2 SLP105 T00001067 $KMWH 171252Z AUTO 18010KT 10SM CLR M01/M07 A2983 RMK AO2 SLP112 T10111072 $KMWH 171152Z AUTO 19014G21KT 10SM CLR 00/M07 A2985 RMK AO2 SLP119 T00001067 10000 21061 58020 $KMWH 171052Z AUTO 19012KT 10SM CLR M01/M07 A2988 RMK AO2 SLP129 T10061067 $KMWH 170952Z AUTO 19015G22KT 10SM CLR 00/M07 A2989 RMK AO2 SLP135 T00001067 $KMWH 170852Z AUTO 19008KT 10SM CLR M01/M07 A2991 RMK AO2 SLP142 T10111067 58018 $KMWH 170752Z AUTO 17006KT 10SM CLR M04/M08 A2993 RMK AO2 SLP152 T10441078 400111156 $KMWH 170652Z AUTO 16006KT 10SM CLR M06/M09 A2996 RMK AO2 SLP162 T10561089 $KMWH 170552Z AUTO 17006KT 10SM CLR M05/M09 A2997 RMK AO2 SLP166 T10501089 10006 21050 58009 $KMWH 170452Z 18006KT 10SM CLR M03/M08 A2998 RMK AO2 SLP171 T10331083 $KMWH 170352Z 18010KT 10SM BKN070 M02/M08 A2999 RMK AO2 SLP175 T10171078 $KMWH 170252Z 19009KT 10SM SCT095 M01/M08 A2999 RMK AO2 SLP176 T10111083 56006 $KMWH 170152Z 18009KT 10SM CLR M01/M09 A3000 RMK AO2 SLP178 T10111089 $KMWH 170052Z 19009KT 10SM FEW100 M01/M10 A3001 RMK AO2 SLP179 T10061100 $KMWH 162352Z 20012G18KT 10SM OVC085 01/M10 A3001 RMK AO2 SLP180 T00061100 10011 21089 56010 $KMWH 162252Z 19012KT 10SM BKN100 01/M10 A3001 RMK AO2 SLP181 T00061100 $KMWH 162152Z 20005KT 10SM BKN100 M02/M09 A3002 RMK AO2 SLP184 T10171089 $KMWH 162052Z 00000KT 10SM BKN100 M02/M09 A3004 RMK AO2 SLP191 T10221089 58009 $

  7. STABLE & UNSTABLE AIR • A stable atmosphere resists any upward or downward displacement. • An unstable atmosphere allows an upward or downward disturbance to grow into a vertical, or convective, current.

  8. STABILITY • STABLE • UNSTABLE • NEUTRAL • Depends on the relationship between the temperature of the rising air parcel of air and the temperature of the surrounding air through which it rises. The temperature of the surrounding air is indicated by the environmental lapse rate ELR.

  9. REACTION OF STABLE AND UNSTABLE AIR TO LIFT

  10. TERMS • STEEP LAPSE RATE • SHALLOW LAPSE RATE • INVERSION • ISOTHERMAL LAYER • ABSOLUTE STABILITY • ABSOLUTE INSTABILITY AND CONDITIONAL INSTABILITY

  11. EXAMPLES OF ELR’S

  12. DEGREE OF STABILITY

  13. ADIABATIC CHANGE • Any time air moves upward, it expands because of decreasing atmospheric pressure. • Heat is transferred in the air and is neither added nor taken from an outside source • Heating and cooling is done by compression and expansion or Adiabatically.

  14. ADIABATIC CHANGE • Adiabatic cooling - rising air cools because of expansion • Adiabatic heating - descending air warms because of compression • Dry adiabatic lapse rate (unsaturated air) cools at 5.4º F / 1000 feet or 3º C / 1000 feet

  15. SATURATED AIR • Has a lower adiabatic lapse rate • Lift a parcel of air, air cools to the dew point, moisture condenses (condensation occurs) • latent heat from vapor to water releases heat and lowers the lapse rate

  16. SATURATED AIR • Saturated adiabatic lapse rate of cooling is less in warm air than in cold air due to warm air releasing more latent heat to offset expansional cooling than does the scant moisture in saturated cold air. • Usually about half the value of the DALR

  17. Temp. (° C) -40 -30 -20 -10 0 5 10 15 20 25 30 35 40 Spec. Hum. (g/kg) 0.1 0.3 0.75 2 3.5 5 7 10 14 20 26.5 35 47 Saturation Specific Humidity versus Temperature in the Atmosphere

  18. SATURATED AIR

  19. Chinook wind - is a katabatic wind • Reason the wind is warmer on one side of the rocks is due to the difference in adiabatic cooling

  20. STABILITY AND INSTABILITY • Cause of instability? • Parcel of air is lifted mechanically • The parcel will cool adiabatically because of expansion • What happens to the temp of the air, after this is what determines the stability

  21. STABILITY AND INSTABILITY • If the parcel is warmer than the ambient air it will continue to rise - thus unstable • if the parcel is the same temp as the ambient air it is neutrally stable • if the parcel is cooler than the ambient air it will sink - thus stable

  22. STABILITY AND INSTABILITY

  23. DAYTIME HEATING AND NIGHT-TIME COOLING

  24. STABILITY AND INSTABILITY • Orographic lifting - is an air mass being forced up a mountain slope • Cooling from belowincreases stability • Heating from belowdecreases stability • Thermals are a sign of instability • Inversions are an example of stability

  25. CLOUDS SIGNPOSTS OF THE SKY • Stable air = stratiform clouds, poor vis, steady precip, smooth ride • Remember as air is lifted if there is no Latent heat it cools at the same rate or faster it will be stable • Unstable air = cumuluform clouds, good vis, showery precip, turbulence

  26. CHARACTERISTICS OF STABLE AND UNSTABLE AIR

  27. CLOUDS SIGNPOSTS OF THE SKY • Remember as air is lifted because of Latent heat it cools slower • this causes further instability • this continues until: • 1. The temp matches or gets cooler than the ambient temp or • 2. It hits a cap of stable air • Sometimes it will be strong enough to push into the stable air causing embedded T storms

  28. DETERMINING BASES • Temp and dew point converge at a rate of about 4.4º F or 2. 2º C • Skew T Log P Charts (Adiabatic Charts) • Today the information is done automatically with computer.

  29. CHAPTER 9 TURBULENCE

  30. TURBULENCE • Turbulence = A conditon of fluid flow in which the flow is not smooth. The velocity of the flow changes rapidly, and the flow direction often reverses itself. • This can cause a minor disturbance to passangers or crew, or even sever structural damage. • First rule of flying in turbulence is to reduce your speed below Va

  31. 3 MAIN CAUSES • 1. Convective currents • 2. Obstructions to wind flow • 3. Wind shear • Can also find in the wake of moving aircraft (wake turbulence)

  32. CONVECTIVE CURRENTS • By definition they involve heat exchange • Usually vertical movement of air up and down • An example is a Thermal • Cold air moving over a warmer surface • different variations in terrain give off different amounts of radiation

  33. MEMORIZE • Barren surfaces such as sandy or rocky wastelands and plowed fields become hotter than open water or ground covered by vegetation.

  34. CONVECTIVE CURRENTS • Barren surfaces such as sandy or rocky wastelands and plowed fields become hotter than open water or ground covered by vegetation (colder).

  35. CONVECTIVE CURRENTS • Cumulonimbus clouds = greatest turbulence (1000-9000 +fpm) • Most active on warm afternoons, light winds • Barren surfaces such as sandy or rocky wastelands and plowed fields become hotter than open water or ground covered by vegetation.

  36. CONVECTIVE CURRENTS • The reason being is that the Albedo of the surfaces is different. This uneven heating of the surface causes convective currents and turbulence. • Albedo = The percent of radiation returning from a surface compared to that which strikes it.

  37. CONVECTIVE CURRENTS • A common cause of turbulence, especially at low altitudes, causes by localized vertical air movement is called convective currents.

  38. DISRUPTION OF WIND FLOW • Usually the faster the wind the more turbulence can be expected • Much like water flowing over and around a rock in a stream • Watch for buildings along a runway • Especially buildings upwind in the final approach path • Trees are another good thing to watch

  39. DISRUPTION OF WIND FLOW

  40. DISRUPTION OF WIND FLOW

  41. MOUNTAIN WAVE • Forms on the leeward side • Like waves on a lake • Altocumulus standing lenticular or Rotor cloud • 40 kts or greater expect mountain wave • 25 kts or greater expect turbulence

  42. MOUNTAIN WAVE

  43. DISRUPTION OF WIND FLOW • Mountain flying • Cross a 3000 to 5000 above crest • some say 2000 to 4000 • Take height of mountain above terrain / 2 = crossing height • Cross ridge line at 45º angle then 90º • Mountain passes and valleys, stay right, be prepared know your elevations prior to takeoff and always have an out.

  44. WIND SHEAR • May be at any altitude • May be at any direction • Measured in feet per second • Some aircraft manuals have provisions for figuring max speed based on 30 fps or 40 fps gusts.

  45. WIND SHEAR • 1. Low level Temp inversion • warm air over cold mixing in the layer • check your winds aloft and area forecasts to get the complete picture • If you see 25 kts or higher 2000-4000 agl and calm surface winds it’s a good bet for a shear zone.

  46. WIND SHEAR • 2. Frontal Zone • wind changes abruptly in a frontal zone • Fast moving cold front is the worst • There is almost always some indication of a fast moving cold front • A squall line may be associated with this type of front • A low dust cloud with a sharp leading edge

  47. WIND SHEAR • 3. Clear Air Turbulence • This can not be seen so no warning • Associated with the jet stream • The worst shear is found in an upper level trough on the polar side of the jet • This is where the temp differential is the greatest in the shortest amount of distance

  48. WIND SHEAR • 4. Low level wind shear • This is mainly associated with thunderstorm activity • Microburst may have downdrafts up to 6000 fpm • Like a garden hose pointed at a sidewalk • Calm wind shears to a headwind which then shears to a tailwind

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