Clouds and More Clouds AOSC 200 Tim Canty. Class Web Site: Lecture 12 Oct Hot air rises!

Transcription

1 Clouds and More Clouds AOSC 200 Tim Canty Class Web Site: Topics for today: How to make clouds pt 1. Lecture 12 Oct Hot air rises! What happens then? 2

2 Dry Adiabatic Lapse Rate As an air parcel rises, it expands into lower pressure air. As it expands, all of the energy inside is spread out over a larger volume so the temperature drops If there s no interaction between the air inside the parcel and the outside environment the process is said to be adiabatic Fig 6.2 Weather: A Concise Introduction 3 Dry Adiabatic Lapse Rate The drop in temperature is called adiabatic cooling. What is it called when temperature decreases with height? Lapse Rate In this case, the specific term is Dry Adiabatic Lapse Rate And has a value of 10 C per km Fig 6.2 Weather: A Concise Introduction 4

3 Dry Adiabatic Lapse Rate For every kilometer increase, the temperature inside the parcel cools by 10 C The environmental lapse rate is 6.5 C per km. The air inside the parcel cools more quickly than the air outside. Fig 6.2 Weather: A Concise Introduction 5 Dry Adiabatic Lapse Rate For every kilometer decrease, the temperature inside the parcel warms by 10 C The environmental lapse rate is 6.5 C per km. The air inside the parcel warms more quickly than the air outside. Fig 6.3 Weather: A Concise Introduction 6

4 Dry Adiabatic Lapse Rate When the air parcel cools, what will happen the RH inside the parcel? Fig 6.2 Weather: A Concise Introduction 7 Dry Adiabatic Lapse Rate When the air parcel cools, what will happen the RH inside the parcel? The saturation vapor pressure inside the parcel decreases as temperature decreases. RH humidity increases inside the rising parcel but not outside the parcel Fig 6.4 Weather: A Concise Introduction 8

5 Dry Adiabatic Lapse Rate When the air parcel subsides (falls toward the surface) the parcel shrinks because of the higher pressure. Temperature inside the parcel increases and the saturation vapor pressure increases. RH goes down; the parcel dries out Fig 6.6 Weather: A Concise Introduction 9 Saturated Adiabatic Lapse Rate What happens when the RH reaches 100% but the parcel keeps rising? The parcel still cools at 10 C per km but What is released when water vapor condenses??? Latent heat and the parcel gains 4 C/km so overall the parcel only cools at 6 C This is the Moist or Saturated Adiabatic Lapse Rate Fig 6.6 Weather: A Concise Introduction 10

6 Real World Example As air rises up a mountain side, it cools at the dry adiabatic lapse rate Once it reaches saturation, it cools at the saturated lapse rate. Also, precipitation (rain or snow) falls out of the cloud and the vapor pressure decreases Fig 6.7 Weather: A Concise Introduction 11 Real World Example The air parcel has lost a lot of water. As it sinks down the mountain side, the air in the parcel warms and dries out the cloud. The parcel warms only at the dry lapse rate. When the parcel reaches the ground, it s warmer than when it started Fig 6.8 Weather: A Concise Introduction 12

7 Real World Example Fig 6.9 Weather: A Concise Introduction 13 Rain Shadow Fig 6.10 Weather: A Concise Introduction 14

8 Chinook (a type of Foehn wind) Air rushing down the downwind side of the mountain warms and dries as it sinks (compressional heating) leading to warm surface winds Fig 7.11: Essentials of Meteorology 15 Cloud Development: Orographic Lifting Air is forced up the side of a mountain and cools as it rises Fig 5.10: Essentials of Meteorology 16

9 Cloud Development: Convergence When wind meets from different directions, the air in between has no place to go but up When the leading edge of the wind slows down, the wind behind piles up Fig 6.11 Weather: A Concise Introduction 17 Cloud Development: Frontal Lifting Warm air will ride up over cold air Fig 6.12 Weather: A Concise Introduction 18

10 Cloud Development: Convection As surface air is warmed by the sun, it becomes less dense and rises Fig 5.10: Essentials of Meteorology 19