Mountain waves and sundowners. “All hell broke loose" City Fire Chief Andrew DiMizio, May 8 2009.

Slides:



Advertisements
Similar presentations
LAB 6 10/16. Stability – Lapse Rate The rate at which a parcel cools as it rises. A dry* parcel cools at 10 degrees Celsius per kilometer***. A moist**
Advertisements

Chapter 5 Atmospheric Moisture. The process whereby molecules break free of liquid water is known as evaporation. The opposite process is condensation,
Cloud Development and Forms
Down-Slope Windstorms
Ch 5 – Vertical Motion & Stability
Atmospheric Stability
Stability & Movement Figure 7.1 A rock, like a parcel of air, that is in stable equilibrium will return to its original position when pushed. If the rock.
Atmospheric Stability
Moist Processes ENVI1400: Lecture 7. ENVI 1400 : Meteorology and Forecasting2 Water in the Atmosphere Almost all the water in the atmosphere is contained.
Lecture 13: Map discussion + Cloud development and forms (Ch 6) Quiz 2 next Friday 13 Oct covers to end of Ch. 6 map discussion (situation of Thurs 5 Oct)
Tephigrams ENVI1400 : Lecture 8.
Stability & Skew-T Diagrams
Textbook chapter 2, p chapter 3, p chapter 4, p Stability and Cloud Development.
Outline Further Reading: Chapter 06 of the text book - stability and vertical motions - five examples - orographic precipitation Natural Environments:
Precipitation Processes: Why does it fall on us?.
Temperature Lapse rate- decrease of temperature with height:  = - dT/dz Environmental lapse rate (  ) order 6C/km in free atmosphere  d - dry adiabatic.
Thunderstorms ASTR /GEOL Physics of Thunderstorms Two fundamental ideas: Convection Latent heat of vaporization/condensation.
Moisture and Atmospheric Stability
Atmospheric Moisture and Stability
METEO 003 LAB 6 Due Friday Oct. 17 th. Chapter 8 Question 1 a,b,c Radiosonde: instrument carried by a weather balloon to measure atmospheric variables.
Warning! In this unit, we switch from thinking in 1-D to 3-D on a rotating sphere Intuition from daily life doesn’t work nearly as well for this material!
II. Synoptic Atmospheric Destabilization Processes Elevated Mixed Layer (EML) Synoptic Lifting Dynamic Destabilization Differential Advection.
Lapse Rates and Stability of the Atmosphere
1 Lake-Effect Snow (LES). 2 Overview of the Lake-Effect Process n Occurs to the lee of the Great Lakes during the cool season n Polar/arctic air travels.
Warm Up 3/14 Which gas is most important for understanding atmospheric processes? a. water vapor c. carbon dioxide b. oxygen d. ozone What is true.
Chapter 6 – Cloud Development and Forms. Cloud Formation Condensation (i.e. clouds,fog) results from:
Atmospheric Stability
Thermodynamics, Buoyancy, and Vertical Motion Temperature, Pressure, and Density Buoyancy and Static Stability Adiabatic “Lapse Rates” Convective Motions.
Chapter 4 Moisture and Atmospheric Stability. Steam Fog over a Lake.
The Atmosphere: An Introduction to Meteorology, 12th
Moisture and Clouds Weather Unit When you see this megaphone, Click it for audio information Weather Unit When you see this megaphone, Click it for audio.
Atmospheric Stability & Instability
Lesson 15 Adiabatic Processes
1 The Thermodynamic Diagram Adapted by K. Droegemeier for METR 1004 from Lectures Developed by Dr. Frank Gallagher III OU School of Meteorology.
Mountain Waves & Clouds Investigating the occurrence of cloud- producing mountain waves. Alistair Reid.
Objectives Review Vocabulary
Flow Interaction with Topography Fundamental concepts: Mountain.
Lab 6: Saturation & Atmospheric Stability
Section 04 Adiabatic Processes and Stability Lessons 12 & 13.
Humidity Under what conditions do you see the above?
Key Terms and Concepts ELR--Environmental Lapse Rate 5°C-6.5°C/1000 m – temperature of the STILL air as you ascend through the troposphere. ALR--Adiabatic.
Office Hours Tue: 12:30 PM to 2:30 PM Wed: 9:00 AM to 10:30 AM & 12:00 PM to 2:00 PM Thr: 9:00 AM to 10:30 AM Course Syllabus can be found at:
Weather & Climate LECTURE 2 Moisture in the Atmosphere Evaporation and Condensation: accompanied by absorption/liberation of heat evaporation: energy.
Exam 2 Review AOS 121 November Geostrophic Balance and Geostrophic Winds Balance between the pressure gradient force and Coriolis force Will.
5.01 Heating and Cooling of the Atmosphere
Photo: Pamela R. Cox 2013 Elizabethtown, Kentucky.
Lecture 4 Precipitation (1)
Atmospheric Stability Terminology I Hydrostatic Equilibrium –Balance, in the vertical, between PGF and gravity –The general state of the atmosphere –Net.
Mountain windstorms Downslope windstorms: general term of a windstorm in which air flows down the side of a mountain. Local names include: Foehn: Alps.
Chapter 9 Winds: Small scale and local systems. Scales of motion Smallest - microscale (few meters or less) Middle - Mesoscale (few to about 100 km) Large.
Atmospheric Stability The resistance of the atmosphere to vertical motion. Stable air resists vertical motion Unstable air encourages vertical motion.
Skew T Log P Diagram AOS 330 LAB 10 Outline Static (local) Stability Review Critical Levels on Thermodynamic Diagram Severe Weather and Thermodynamic.
Vertical Motion and Temperature Rising air expands, using energy to push outward against its environment, adiabatically cooling the air A parcel of air.
Atmospheric Stability and Air Masses
+ Moisture and Stability Chapter 4. + The Hydrologic Cycle Hydrologic Cycle: the circulation of Earth’s water supply The cycle illustrates the continuous.
Meteo 3: Chapter 8 Stability and Cloud Types Read Chapter 8.
Chapter 6 Stability and Cloud Development. Stability & Cloud Development This chapter discusses: 1.Definitions and causes of stable and unstable atmospheric.
Chapter 4 Moisture and Atmospheric Stability
A Major Component of Earth’s Weather. The Hydrologic Cycle Water can exist as a solid, liquid, or gas on Earth. The movement of water from different reservoirs.
Cloud Formation: Lifting Processes Atmospheric Lifting In order for air to form clouds, the air must be lifted and rise in altitude There are 4 types.
Monday’s lesson (At the end the lesson you will be able to…) Describe the changes in temperature with height through the lower layers of the atmosphere.
Lesson 1 Task 1 Can you draw a fully labelled diagram to show the ‘day model’ of radiation balance in the earth’s energy budget in 5 minutes on these.
Stability and Cloud Development
Chapter 18.2 Cloud Formation.
Bellwork 4/10 Please, turn in your Sling Psychrometer Lab
Stability and Cloud Development
Atmospheric Moisture Atmospheric moisture is a very important topic under the theme of climatic system. In this presentation, you can make use of photos.
Atmospheric Stability & Instability
Downslope windstorms:
Atmospheric Stability
Presentation transcript:

Mountain waves and sundowners

“All hell broke loose" City Fire Chief Andrew DiMizio, May

Important concepts to review Adiabatic lifting (or adiabatic expansion) Adiabatic sinking (or adiabatic compression) Saturation mixing ratio, temperature, dew point and relative humidity Stability of the atmosphere

H=0 T=30 o C H=100m, T=29 o C H=200m, T=28 o C H=300m T=27 o C H=400m T=26 o C  Air parcel lifts due to increase in buoyancy (warmer and less dense than the surrounding environment)  Volume expands and work is done against the environment.  This occurs too fast to transfer or receive heat from the environment  Because no heat is transferred from or to the air parcel, volume increases and the air mass inside the air parcel cools down  This is known as adiabatic lifting Adiabatic lifting (adiabatic expansion) Dry adiabatic lapse rate: 10 o C/km or 1 o C/100m

Adiabatic compression  Air parcel sinks  Volume decreases due to the work done by the environment  This occurs too fast to transfer or receive heat from the environment  Because no heat is transferred from or to the air parcel, volume decreases and the air mass inside the air parcel warms up  This is known as adiabatic compression or adiabatic sink H=0 T=30 o C H=100m, T=29 o C H=200m, T=28 o C H=300m T=27 o C H=400m T=26 o C Dry adiabatic lapse rate: 10 o C/km or 1 o C/100m

The air’s susceptibility to uplift is called its static stability. Statically unstable air becomes buoyant when lifted and continues to rise if given an initial upward push. Statically stable air resists upward displacement and sinks back to its original level when the lifting mechanism ceases. Statically neutral air neither rises on its own following an initial lift nor sinks back to its original level; it simply comes to rest at the height to which it was displaced.

When a parcel of unsaturated or saturated air is lifted and the Environmental Lapse Rate (ELR) is greater than the dry adiabatic lapse rate (DALR), the result is absolutely unstable air. T=9 o C T=8 o C T=7 o C Note that in this case the air parcel is warmer than the environment and will continue to rise

When a parcel of unsaturated or saturated air is lifted and the Environmental Lapse Rate (ELR) is less than the saturated adiabatic lapse rate (SALR), the result will resist lifting is absolutely stable air and the parcel will resist lifting. 7o C7o C7o C7o C 8oC8oC8oC8oC 9oC9oC9oC9oC

Assume the ELR is 0.7 °C/100 m and the air is unsaturated. As a parcel of air is lifted, its temperature is less than negative buoyancy that of the surrounding air, so it has negative buoyancy. 7oC7oC7oC7oC 8oC8oC8oC8oC 9oC9oC9oC9oC

9.3 o C 8.9 o C 8.8 o C 10.0 o C 10 C 9.0 C 8.0 C 7.0 C Force parcel upward Temperature inversion Stable atmosphere V V V

Horizontal Atmospheric motion

Tridimensional view Northern Hemisphere

Pressure (height) variations in upper atmosphere mainly caused by temperature variations in lower atmosphere Ridges have warm air below Troughs have cold air below

Typical temperature Humidity daily variation ACTUAL Relative humidity, RH, relates the ACTUAL amount of water vapor in the air to the maximum possible at the current temperature. RH = (specific humidity/saturation specific humidity) X 100%

Winds accelerate along canyons

The Jesusita Fire

Although it is composed of gases, in many ways the atmosphere behaves like a fluid. Many atmospheric disturbances occur as waves. These atmospheric wave disturbances result from the interactions of several forces including pressure gradients, Coriolis force, gravity, and friction. Atmospheric waves occur on a full range of spatial scales. You are probably familiar with large-scale planetary and synoptic waves found on constant pressure charts. In these waves, the horizontal motions exceed the vertical motions by several orders of magnitude. Sundowner and Santa Ana winds are considered mountain waves. When wind speeds are intense, they are often referred to as “wind storms” What is a mountain wave?

Mountain waves form above and downwind of topographic barriers when strong winds blow with a significant vector component perpendicular to the barrier in a stable environment Wave activity Cap clouds may indicate mountain waves

The vertically-propagating wave is often most severe just downwind of the mountain barrier. These waves frequently become more amplified and tilt upwind with height. Tilting, amplified waves can cause aircraft to experience turbulence at very high altitudes. Clear air turbulence often occurs near the tropopause due to vertically-propagating waves.

Vertically-propagating waves with sufficient amplitude may break in the troposphere or lower stratosphere. Wave-breaking can result in severe to extreme turbulence within the wave-breaking region and nearby, typically between 20,000-40,000 feet ( m). If a vertically-propagating wave doesn't break, an aircraft would likely experience considerable wave action, but little turbulence.

Strong downslope wind cases are associated with strong cross-barrier flow, waves breaking aloft, and an inversion near the barrier top. This may be double or triple the wind speed at mountaintop level. These high winds frequently lead to turbulence and wind shear at the surface. Downslope windstorms often abruptly end at the "jump region”. The jump region is an extremely turbulent area that can extend up to 10,000 feet.

Rotors are also called horizontal roll vortices because they form a complete rotational pattern, with the axis of rotation parallel to the ground. They exist immediately downstream of the jump region and under a wave crest. Smaller-scale rotations embedded within the low- level turbulent zone can cause rolling that exceeds an aircrafts ability to stay level.

Lee waves whose energy does not propagate vertically because of strong wind shear or low stability above are said to be "trapped." Trapped lee waves are often found downstream of the rotor zone, although a weak rotor may exist under each lee wave. Strong turbulence can develop between the bases of associated lenticular clouds and the ground. Lenticular clouds form near the crests of mountain waves. As air ascends and cools, moisture condenses, forming the cloud. As that air descends in the lee of the wave crest, the cloud evaporates.

This photo, taken during the Sierra Wave Project in the 1950s, shows a dramatic example of a downslope windstorm in the Owens Valley, California. The wind accelerates down the lee slope of the Sierra Nevada on the right. Dust is seen being picked up off the floor of the valley and lifted in the "jump region" into the highly turbulent flow under rotor clouds.

The warming of downslope winds typically occurs when low-level air upwind of a barrier is blocked and does not proceed up and over. Instead, the downslope winds originate near or above mountain-top level. As this air descends the lee slope, it warms following a dry adiabatic lapse rate of 10°C per kilometer. Under stable atmospheric conditions, the lapse rate upstream of the barrier will be substantially less than 10°C per kilometer. The end result is warmer temperatures on the lee side of the mountain barrier, much warmer if an inversion is present on the windward side.

Cold downslope winds are called bora winds. They result from a deep and very cold upstream air mass that spills over a barrier and displaces a warmer air mass. Unlike a foehn wind, the upstream air mass is so cold that the air reaching the ground along the lee slope feels cool, despite warming adiabatically as it descends.

Santa Barbara Sundowner Winds Generic Classification (Einar Hovind, Gary Ryan) SMX – SBA SLP Gradient Wind Ranges (m s -1 )  2 mb No downslope winds 2-3 mb mb mb20-25  5 mb  25 They typically occur in spring and summer seasons. North or northwest winds across Santa Inez Mountains with strong surface pressure gradient (e.g. Santa Maria and Santa Barbara). Increase in surface temperature and decrease in relative humidity

30 History of Severe Sundowners 17 June 1859 T  138ºF (???) Sept T  108ºF (4PM) T  102ºF (8PM) 2-3 July 1907 T  88ºF (Midnight) June 1917 T  115ºF (5PM) all time SB T record July 1925 T> 100ºF Gusts mph 26 July 1977 Gusts mph May 2009 will likely be part of the history of strong events T> 100oF and Gusts 40mph

31 Santa Barbara Painted Cave Fire 27 June 1990 Point of origin: Old San Marcos Rd. and Hwy 154 6:02 pm PDT. T=96°F, RH=10%, mph 6:45 pm fire advanced 2 miles, winds 60 mph SBA T=109°F (42.7 °C) 1:30 pm. 30 mph (13 ms-1) 3:48pm. El Capitan 116 °F (46.6 °C). San Marcos summit mph. South side 60 mph Tucker’s Grove 80 mph (35 ms-1)  1 death, consumed over 600 structures, burned 4,900 acres. Arson ignited

Numerical simulation of Sundowner winds

33

Conclusions: Work with your group on the main conclusions about this lecture: Can you explain what is stability in the atmosphere and its importance for cloud formation? Can you explain the reasons for turbulence in the atmosphere? Can you explain the reasons why sundowners are associated with dry and warm days in SB? Do you remember what are the main dynamical factors associated with sundowners?