# Presentation: 502348

## Basic Meteorology

- Processes that influence air quality
- Sunlight
- Horizontal dispersion
- Vertical Mixing
- Transport
- Large scale to local scale

## Basic Weather

- Aloft ridges and troughs
- Rising and sinking air
- Surface highs and lows
- Vorticity
- Mixing and temperature soundings
- Ridges, troughs, and temperature soundings
- Winds
- Synoptic scale
- Meso/Urban scale
- Transport (surface and aloft)

**Notes:**
Relate to processes on prior slide

## Aloft Ridges and Troughs

- Mountains and valleys of warm and cool air
- The height of the 500-mb pressure altitude depends on the relative temperature of the column

**Notes:**
1.  Columns of cool and warm air

## Aloft Ridges and Troughs

- Air travels faster around ridges and slower around troughs
- Areas of aloft convergence and divergence
- Waves (ridges and troughs) generally move west to east

**Trough**

## Aloft Ridges and Troughs

- Aloft divergence causes rising motion and surface low
- Aloft Convergence causes sinking motion and a surface high
- Surface pressure patterns are offset from aloft patterns

## Rising and Sinking Air 

- Sinking motion
- Warms the air
- Creates a temperature inversion
- Reduces vertical mixing
- Creates clear skies
- Associated with poor air quality
- Rising motion
- Cools the air
- Breaks inversions
- Increases mixing
- Causes cloud cover
- Associated with good air quality

**Notes:**
Besides sinking causing the surface highs ......

## Surface Highs and Lows – Relationship to Aloft Pattern

- 500 mb heights on the afternoon of January 7, 2002 (00Z Jan 8)

- Surface pressure on the afternoon of January 7, 2002 (00Z Jan 8)

- High PM2.5 in Salt Lake City, Utah

**Notes:**
January 7, 2002   24-hr avg = 32 ug/m3
show area of convergence and sinking
Dome of warm air,  inter-mountain west

## Surface Highs and Lows – Relationship to Aloft Pattern

- Low PM2.5 in Salt Lake City, Utah

- 500 mb heights on the afternoon of January 22, 2002 (00Z Jan 23)

- Surface pressure on the afternoon of January 22, 2002 (00Z Jan 23)

- Surface Highs and Lows – Relationship to Aloft Pattern

**Notes:**
January 22, 2002   24-hr avg = 9 ug/m3
Low over s. colorado  moved through area

## Vorticity – Subtleties of Ridges and Troughs

- Vorticity is the measure of rotation
- Captures smaller-scale aloft features within larger patterns
- Subtle changes in an upper-level pattern can have a large influence on air quality
- Negative vorticity is associated with sinking motion (Less than 10 1x10-5 s-1 on charts)
- Positive vorticity is associated with rising motion (Greater than 10 1x10-5 s-1 on charts)
- Movement of vorticity is what is important

**Notes:**
Shown really nice trough, but things are never that clear in the atm.

## Vorticity – Example of Negative and Positive

- Ahead of **Positive Vorticity** =
- Rising Motion =
- Good Mixing = **Good AQ**

- Ahead of **Negative Vorticity** =
- Sinking Motion =
- Reduced Vertical Mixing = **Poor AQ**

- 500-mb heights and vorticity for January 7, 2002 (00Z Jan 8).  Heights are in meters (solid) and vorticity is in 1x10-5 s-1 (dashed).  The “N” denotes a local vorticity minimum and the “X” denotes a local vorticity maximum.

- 500-mb heights and vorticity for January 22, 2002 (00Z Jan 23).  Heights are in meters (solid) and vorticity is in 1x10-5 s-1 (dashed).  The “N” denotes a local vorticity minimum and the “X” denotes a local vorticity maximum.

**Notes:**
Vorticity advection and vert motion

Forecasting in southern areas -  weak systems - small troughs and ridges as indicated by vort critical

## Ridges and Temperature Soundings

- Ridge =
- Sinking =
- Strong Inversion =
- Poor  AQ

**University of Wyoming**

**Notes:**
Ack tons of lines
point out  couple features
Strong inversion all day
1200 m MSL  Inversion at 850 mb 1500 m

## Troughs and Temperature Soundings

- Td T

- Td      T

- Trough=
- Rising =
- Weak Inversion=
- Good AQ

**University of Wyoming**

**University of Wyoming**

**Notes:**
No inversion in morning, very little of one in evening

## Mixing and Temperature Soundings – Estimating Mixing Height

- _Holtzworth Method_ – Starting at the forecasted maximum temperature, follow the dry adiabat (dashed line) until it crosses the morning sounding.   This is the estimated peak mixing height for the day.
- The dry adiabatic rate is how an unsaturated air parcel cools as it rises.  It is defined as -9.8 oC per km.

**Notes:**
Explain dry adiabat and parcel temp change as rises

## Mixing and Temperature Soundings 

- RL	 = Residual Layer
- CBL	 = Convective Boundary Layer
- NBL	 = Nocturnal Boundary Layer

- Mixing and Temperature Soundings

- Pollutants mix into large volume resulting in low pollution levels

- Weak Inversion

- Sunrise

- Sunset

**Height**

- Midnight

**Inland**

- Temperature soundings

**Notes:**
Putting it all inversion and mixing GO SLOW ANIMATE

## Winds

- Horizontal dispersion and transport
- Synoptic scale
- Winds driven by large high- and low-pressure systems
- Meso-scale
- Land/sea or lake breeze
- Mountain/valley
- Terrain-forced
- Surface vs. boundary layer
- Transport at different levels
- Mixing during the day

**Notes:**
Meso-scale important to local aq

## Winds – Examples of Synoptic Patterns and Wind Flow 

- Winds – Examples of Synoptic Patterns and Wind Flow

**Low **
**ozone**

**High **
**ozone**

**High **
**ozone**

**Moderate**
**ozone**

- MacDonald et al, 1998
- Comrie and Yarnal, 1992

**Notes:**
Focus on Mid-Atlantic region

## Winds – Transport

- 24-hr air parcel paths for a June 2001 ozone episode based on NOAA’s Hysplit Trajectory Model.

**Notes:**
Explain trajectory and background
Explain dates and 24 hour transport
Dirty air coming in not clean

## Winds – Meso and Urban Scales

- Meso/urban scales = regions, bays, metropolitan regions, terrain
- Local flows (stagnation, recirculation) are very important for air quality predictions
- Local forcing can dominate flow patterns when synoptic pressure gradients are weak
- Local flows often follow diurnal heating and cooling cycles
- Local flows are often difficult for weather models to predict but can be predicted by forecasters with knowledge of the area

## Winds - Land/Lake Breeze

**Surface winds on July 18, 1991 at (a) 0600 CDT and (b) 1500 CDT.  Peak ozone concentrations on this day were about 170 ppb.  (Dye et al., 1995).**

## Winds - Trough and a Persistent Delta Breeze

- Radar profiler wind data at Franklin Field, California, on July 17, 1998.  Notice the demise of the delta breeze at about 0800 PST and the return of the delta breeze at about 1100 PST below about 500 m.  MacDonald et al., 1999.

- 500-mb trough approaching the coast enhances the sea-breeze inflow into the central valley of California.

**Notes:**
Clean out day  
Not a high ozone case
Another way to look at flows

## Winds - Recirculation Associated with Land/Sea Breeze Circulation

- Forward 120-m agl and 505-m agl trajectories from downtown Houston (0600 to 1800 CST on August 29, 1998).  Peak ozone concentrations and times of peak concentration (begin hour CST) at each monitoring site are shown  (MacDonald et al, 2001).

**Notes:**
Another way to look at flows
Note low level flow and high level flow
Relate to box , and emissions loading

## Summary - Meteorology Associated with Poor AQ

**Notes:**
Animate

## Summary - Meteorology Associated with Good AQ

## Summary

- Next step
- Obtaining and interpreting forecast information
- Questions

- Processes that influence air quality
-   Large-scale weather pattern
-   Surface highs and lows
-   Vertical mixing
-   Winds/Transport