# Presentation: 274545

## Basic Meteorology

- Prepared by:
- Clinton P. MacDonald and Charley A. Knoderer
- Sonoma Technology, Inc.
- Petaluma, CA
- The 2005 National Air Quality Conference
- Forecasting Short Course
- San Francisco, CA
- February 13, 2005

## Goal

- To explain how to interpret basic weather
- information to forecast air quality using
- Soundings
- Weather charts

## Box Model Concept

- Key Processes
- Source location, density, and strength
- Dispersion (horizontal mixing) - wind speed
- Sunlight
- Stability
- Vertical mixing - inversion

- Concentration  S/WS

- Wind speed (WS)

- Concentration  S/VM

- Vertical mixing (VM)

- Courtesy of New Jersey
- Department of Environmental Protection

- S

- S

## Soundings

- Observed: Typically measured using instrument called a rawinsonde
- Instruments carried by a balloon up through the atmosphere, equipped with sensors to measure meteorological variables (pressure, temperature, relative humidity, wind, etc.), and provided with a radio transmitter for sending this information to the observing station
- Launched at 0000 and 1200 UTC
- Forecast: RUC, Eta, Meso-eta, GFS, UKMet
- RUC, every 1 hour through 12 hours
- Eta, every 3 hours through 84 hours
- NGM, every 12 hours through 48 hours
- Aviation, every 6 hours through 180 hours, every 12 hours 180 hours through 384 hours
- For air quality forecasting, focus on 700 mb (~3000 m) and below

## Diurnal Temperature Soundings

## Lapse Rates

- Adiabatic Lapse Rate:  The rate at which an unsaturated air parcel cools as it rises.  It is minus 9.8oC per km.
- Moist Adiabatic Lapse Rate: The rate at which a saturated air parcel cools as it rises.
- It varies with the original air temperature of the parcel.
- A commonly used value is 6 ̊C/km.

## Rawinsonde Plots

- Winds

- Temperature grid

- Dry adiabat grid:
- rate at which an
- unsaturated air
- parcel cools as it
- rises.

- Moist adiabat grid:
- The rate at which a saturated air parcel cools as it rises.

- Mixing ratio grid:
- the mass of the water vapor
- in a parcel to the mass of
- dry air

- Pressure level grid

- Temperature scale
-  ( ̊C)

- Pressure scale
- (mb)

- Temperature

- Dew point
- temperature

- Ground level

## Interpreting Rawinsondes

- Temperature
- Inversions
- Stability
- Mixing height
- Winds
- Clouds

## Interpreting Rawinsondes – Temperature

- Warm aloft temperature leads to stable conditions and poor air quality
- Determine the relationship for your area by season

- 850-mb temperature

- = 10.5 ̊C

## Interpreting Rawinsondes – Inversions

- A layer of very stable air over a short vertical distance produced by warmer air above cooler air

## Interpreting Rawinsondes – Inversions

- Types
- Subsidence
- Created by sinking air associated with ridges
- Can limit daytime mixing depth and plays important role in daytime pollutant concentrations
- Nocturnal
- Created by cooling ground at night
- Strongest with clear skies, light winds, and long nights
- Can trap emissions, released during the overnight hours, close to the ground
- Advection
- Created when warm air aloft moves over cooler air below
- Can occur ahead of an approaching cold front
- Can cause poor air quality, despite the lack of an aloft ridge
- Stable conditions in a temperature profile can exist without an inversion

## Interpreting Rawinsondes – Stable Atmosphere

## Interpreting Rawinsondes – Unstable Atmosphere

## Interpreting Rawinsondes – Estimating Mixing Heights from Morning Soundings

- _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 -9.8oC per km.

## Interpreting Rawinsondes – Estimating Mixing Heights

## Interpreting Rawinsondes – Clouds, Fog, and Wind

- Clouds occur when dew point temperature equals temperature

- Clouds

- Decoupled winds

- _Time Winds Weather                     Sky Cover_
- 12:51 Z N 13   Light Rain Fog/Mist
- 11:51 Z N 12   Light Rain                BKN006 OVC011
- 10:51 Z N 10   Light Rain Fog/Mist   OVC004

- Fog

## Rawinsonde Exercise

- Determine the following
- 850-mb temperature
- Inversions
- Afternoon mixing height based on morning temperature sounding, assuming a forecasted high temperature of 18°C
- Afternoon mixing height on afternoon sounding
- Based on findings
- Did the mixing height estimate from the morning sounding match the mixing height determined from the afternoon sounding?

## Rawinsonde Exercise

## Rawinsonde Exercise

- 850-mb temperature = ~3OC
- Forecasted afternoon mixing
- height=~630 mb or ~3800 m

## Weather Charts (1 of 5)

- Depict upper-air and surface meteorological patterns as a horizontal slice of the atmosphere
- Show forecasted meteorological variables at a particular time on a particular pressure level

## Weather Charts (2 of 5)

- 500-mb
- heights
- and vorticity

- 700-mb
- heights and
- vertical
- velocity

- Surface
- pressure

- 850-mb
- heights
- and
- tempera-
- ture

## Weather Charts (3 of 5)

- Surface fronts
- Transition zone between air masses
- Warm air ahead of fronts is often polluted
- Cold air behind fronts is often clean
- Surface pressure and winds
- Good indicator of horizontal dispersion
- Can be used to help determine transport
- Locations where pressure contours are widely spaced have light winds and low dispersion
- If pollutant concentrations upwind of a location are high and the winds are moderately strong, forecasters should evaluate the possibility of transport

## 850-mb temperature
Good indicator of stability
700-mb vertical velocity
Downward vertical motion (negative on charts shown here) indicates stable conditions and is associated with poor air quality
Upward vertical motion (positive on charts shown here) indicates unstable conditions and is associated with good air quality
500 mb heights – the height of the 500-mb pressure surface
Ridges associated with poor air quality
Troughs associated with good air quality

- Good indicator of stability
- 700-mb vertical velocity
- Downward vertical motion (negative on charts shown here) indicates stable conditions and is associated with poor air quality
- Upward vertical motion (positive on charts shown here) indicates unstable conditions and is associated with good air quality
- 500 mb heights – the height of the 500-mb pressure surface
- Ridges associated with poor air quality
- Troughs associated with good air quality

- Weather Charts (4 of 5)

## Weather Charts (5 of 5)

- Analyses and forecasts (various models)
- Eta:	NCEP short-range forecast model
- 		Now running at 12-km resolution with 60 vertical layers
- 		Runs 4 x day (00, 06, 12, 18 UTC)
- 		Forecasts for 00, 06, 12 and 18 UTC out 84 hours
- Time in weather products
- UTC/Zulu/GMT
- Example: 00Z Feb 2 = 1800 CST Feb 1 (For Daylight Savings, 1900 CDT)
- Forecast time periods
- Forecast validation time
- Based on model initialization time (00 or 12 UTC) + Forecast periods 12, 24, 36, 48, 72, 96 hrs., etc.
- Example:  24-hr forecast from a 12 UTC model run is valid at 12 UTC (7 AM EST) the next day

## Interpreting Weather Charts – Surface (1 of 3)

- Interpreting Weather Charts – Surface (1 of 3)

- Strong pressure gradient
- Strong winds can lead to good dispersion and good air quality or can result in transport of poor air quality

- Weak pressure gradient
- Light winds can lead to poor dispersion and poor air quality

## Interpreting Weather Charts – Surface (2 of 3)

- Fronts
- Transition zones between two air masses of differing densities (e.g., temperature, pressure, and humidity)
- Importance to air quality
- Warm air ahead of front is often polluted
- Cold air behind front is usually clean air

## Interpreting Weather Charts – Surface (3 of 3)

- Interpreting Weather Charts – Surface (3 of 3)

## Interpreting Weather Charts – 850-mb Temperature

- Warm 850-mb temperatures can stabilize the atmosphere, which can lead to poor air quality by reducing vertical mixing
- Cool 850-mb temperatures can destabilize the atmosphere, which can lead to good air quality by enhancing vertical mixing

## Interpreting Weather Charts – 700-mb Vertical Velocity

- Downward vertical motion stabilizes the atmosphere which can lead to poor air quality
- Upward vertical motion  destabilizes the atmosphere which can lead to good air quality

- Courtesy of San Jose State University Meteorology Department

## Interpreting Weather Charts – 500-mb Ridges and Troughs (1 of 5)

- 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

## Interpreting Weather Charts – 500-mb Ridges and Troughs (2 of 5)

- Winds travel faster around ridges and slower around troughs
- Areas of aloft convergence and divergence are created.

- Interpreting Weather Charts – 500-mb Ridges and Troughs (2 of 5)

## 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

- Aloft convergence causes sinking motion and a surface high
- Surface pressure patterns are offset from aloft patterns

- Interpreting Weather Charts – 500-mb Ridges and Troughs (3 of 5)

## Effects on air quality
Ridges and associated sinking motion
Warm the air
Create a temperature inversion
Reduce vertical mixing
Create clear skies
Are associated with poor air quality
Troughs and associated rising motion 
Cool the air
Break inversions
Increase mixing
Cause cloud cover
Are associated with good air quality

- Ridges and associated sinking motion
- Warm the air
- Create a temperature inversion
- Reduce vertical mixing
- Create clear skies
- Are associated with poor air quality
- Troughs and associated rising motion
- Cool the air
- Break inversions
- Increase mixing
- Cause cloud cover
- Are associated with good air quality

- Interpreting Weather Charts – 500-mb Ridges and Troughs (4 of 5)

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

## Interpreting Weather Charts – 500-mb Ridges and Troughs (5 of 5)

- Courtesy of San Jose State University Meteorology Department

- Ridges are associated with poor air quality
- Troughs are associated with good air quality

- Ridge

- Trough

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

## Interpreting Weather Charts – 500-mb Vorticity (1 of 2)

- Vorticity is a measure of rotation
- It 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 advection is associated with sinking motion (less than 10 1x10-5 s-1 on charts)
- Positive vorticity advection is associated with rising motion (greater than 10 1x10-5 s-1 on charts)

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

## Interpreting Weather Charts – 500-mb Vorticity (2 of 2)

- Courtesy of San Jose State University Meteorology Department

- Negative
- vorticity is
- associated with sinking motion and poor air quality

- Positive vorticity
- is associated with rising motion and good air quality

- Interpreting Weather Charts – 500-mb Vorticity (2 of 2)

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

## Weather Charts Exercise (1 of 2)

- For Atlanta, Georgia, identify
- Ridge or trough
- 850-mb temperature
- Surface wind direction and strength
- Vertical velocity

## Weather Charts Exercise (2 of 2)

- °C

- °C

- °C

- -μB/s

- _Surface_: temperature (color contours), pressure (solid lines, mb), and winds (barbs, knots).

- _850 mb_: temperature (color contours), geopotential heights (solid lines, dm), and winds (barbs, knots)

- _750 mb_: vertical velocity (color contours), geopotential heights (solid lines, dm), and winds (barbs, knots)

- _500 mb_: temperature (color contours), geopotential heights (solid lines, dm), and winds (barbs, knots)

**Atlanta, GA**

**Atlanta, GA**

## Conclusions

- Soundings and weather charts are the cornerstone of conceptual air quality forecasting
- Soundings
- Aloft temperature and winds
- Stability and Mixing
- Weather Charts
- Surface winds and fronts
- 850 temperature
- 700 vertical velocity
- 500 heights and vorticity

## Links

- Soundings
- _[http://weather.uwyo.edu/upperair/sounding.html](http://weather.uwyo.edu/upperair/sounding.html)_
- _[http://](http://www.rap.ucar.edu/weather/upper/)__[www.rap.ucar.edu](http://www.rap.ucar.edu/weather/upper/)__[/weather/upper/](http://www.rap.ucar.edu/weather/upper/)_
- _[http://](http://vortex.plymouth.edu/uacalplt.html)__[vortex.plymouth.edu/uacalplt.html](http://vortex.plymouth.edu/uacalplt.html)_
- Surface Analyses
- _[http://](http://www.hpc.ncep.noaa.gov/dailywxmap/)__[www.hpc.ncep.noaa.gov/dailywxmap](http://www.hpc.ncep.noaa.gov/dailywxmap/)__[/](http://www.hpc.ncep.noaa.gov/dailywxmap/)_
- _[http://www.rap.ucar.edu/weather/progs/](http://www.rap.ucar.edu/weather/progs/)_
- _[http://](http://weather.unisys.com/index.html)__[weather.unisys.com/index.html](http://weather.unisys.com/index.html)_
- Models
- _[http://www.met.sjsu.edu/weather/models.html](http://www.met.sjsu.edu/weather/models.html)_
- _[http://](http://weather.unisys.com/index.html)__[weather.unisys.com/index.html](http://weather.unisys.com/index.html)_
- _[http://](http://ggweather.com/loops/ncep_loops.htm)__[ggweather.com/loops/ncep_loops.htm](http://ggweather.com/loops/ncep_loops.htm)_
- _[http://](http://www.arl.noaa.gov/ready/cmet.html)__[www.arl.noaa.gov/ready/cmet.html](http://www.arl.noaa.gov/ready/cmet.html)_
- _[http://](http://weather.uwyo.edu/models/)__[weather.uwyo.edu](http://weather.uwyo.edu/models/)__[/models/](http://weather.uwyo.edu/models/)_
- _[http://](http://www.rap.ucar.edu/weather/model/)__[www.rap.ucar.edu](http://www.rap.ucar.edu/weather/model/)__[/weather/model/](http://www.rap.ucar.edu/weather/model/)_