ATM OCN 100 Summer ATM OCN Fall 2001 LECTURE 13 (Con’t.) PRECIPITATION & the PRECIPITATION FORMATION PROCESS A. Introduction B. Background C. Observations & Measurements
ATM OCN 100 Summer Announcements u Homework 4 is: –Posted has been posted on the Web at: – –Due next Wednesday 7 Nov u First Hour Exam –If you have not picked up exam, please do so! –An exam statistics page is posted at: u Homeworks 1- 3: –Please Pick up yours in front (at end of class). –Keys are posted on the Web at: –
MADISON’S CURRENT WEATHER at 900 AM CST FRI NOV Updated twice an hour at :05 and :25 Sky/Weather: SUNNY CLEAR Temperature: 53 F (11 C) Dew Point: 33 F (0 C) Relative Humidity: 46% Wind: VRB5 MPH Barometer: 30.01R
ATM OCN 100 Summer CURRENT IR MICHELLE
ATM OCN 100 Summer TD-15 CURRENT VISIBLE MICHELLE
ATM OCN 100 Summer MICHELLE CURRENT WATER VAPOR
ATM OCN 100 Summer Enhanced IR Satellite Image of Michelle (CIMSS-SSEC)
ATM OCN 100 Summer Forecast Track of Michelle
ATM OCN 100 Summer CURRENT IR MICHELLE
ATM OCN 100 Summer CURRENT VISIBLE MICHELLE
ATM OCN 100 Summer CURRENT WATER VAPOR MICHELLE
ATM OCN 100 Summer Enhanced IR Satellite Image of Michelle (CIMSS-SSEC)
ATM OCN 100 Summer Track of Michelle
ATM OCN 100 Summer Surface Weather Map from Today with Isobars & Fronts
ATM OCN 100 Summer Current Temperatures ( o F) & Isotherms
ATM OCN 100 Summer Current Dewpoints ( o F)
ATM OCN 100 Summer Tomorrow’s 7AM Forecast
ATM OCN 100 Summer Rule of thumb u If you can expect –Clear skies –Near Calm conditions u Then: –The afternoon dewpoint provides a good predictor of the following morning’s low temperature.
ATM OCN 100 Summer Surface Weather Map from Today with Isobars & Fronts
ATM OCN 100 Summer Current Temperatures ( o F) & Isotherms
ATM OCN 100 Summer Current Dewpoints ( o F)
ATM OCN 100 Summer Tomorrow’s 7AM Forecast
ATM OCN 100 Summer Rule of thumb u If you can expect –Clear skies –Near Calm conditions u Then: –The afternoon dewpoint provides a good predictor of the following morning’s low temperature.
ATM OCN 100 Summer Saturday Morning’s Low Overnight Low 33°F Fri AM Dewpoint 33 °F
ATM OCN 100 Summer This Morning’s Low Overnight Low 26°F Sun. Aftn. Dewpoint 23°F
MADISON’S CURRENT WEATHER Madison Weather at 1000 AM CDT 17 JUL 2002 Updated twice an hour at :05 and :25 Sky/Weather: PTSUNNY Temperature: 79 F (26 C) Dew Point: 65 F (18 C) Relative Humidity: 62% Wind: SW5 MPH Barometer: 30.07F ( mb)
ATM OCN 100 Summer Last 24 hrs in Madison FOG
ATM OCN 100 Summer CURRENT VISIBLE
ATM OCN 100 Summer CURRENT IR
ATM OCN 100 Summer Yesterday’s High Temperatures ( ° F)
ATM OCN 100 Summer Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar
ATM OCN 100 Summer Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) L L H H LL H H L L H L L H
ATM OCN 100 Summer Yesterday’s High Temperatures ( o F) – ( ) Average High Temperatures
ATM OCN 100 Summer Current Temperatures ( o F) – 24 Hrs Ago Cold Advection + Drier Air
ATM OCN 100 Summer Current Temperatures ( ° F) & Isotherms (“iso” = equal +”therm” = temperature)
ATM OCN 100 Summer Current Dewpoints ( o F)
ATM OCN 100 Summer Sample Radiosonde Sites
ATM OCN 100 Summer RAPID CITY
ATM OCN 100 Summer GREEN BAY
ATM OCN 100 Summer IFR – Instrument Flight Rules Red Dots: Ceiling < 1000 ft or Visibility < 3 miles
ATM OCN 100 Summer Current Apparent Temperatures ( o F)
ATM OCN 100 Summer Forecast Heat Indices
ATM OCN 100 Summer Tomorrow AM Forecast Map
ATM OCN 100 Summer Announcements u Homework #3 is due today If you have ??, please see me.
ATM OCN 100 Summer ATM OCN Summer 2002 LECTURE 13 PRECIPITATION & the PRECIPITATION FORMATION PROCESS A. INTRODUCTION Statement of the Problems –What is precipitation? –Why is precipitation important? –How is precipitation formed? –How is precipitation measured?
ATM OCN 100 Summer B. BACKGROUND u Precipitation is –Liquid or solid water that falls from sky; –Examples: Rain, drizzle, snow, hail, ice pellets (sleet), freezing rain. u Precipitation is not: –Liquid or solid water that forms on surfaces; –Examples: Dew, frost, fog.
ATM OCN 100 Summer B. BACKGROUND (con’t.) u Importance of Precipitation u Meteorological Significance u Human Significance –Drought –Floods
ATM OCN 100 Summer C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges –Standard rain gauge; –Tipping bucket; –Weighing bucket. u Doppler Radar-estimated rainfall u Satellite-estimated rainfall
ATM OCN 100 Summer C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges … such as…
ATM OCN 100 Summer Simple Rain gauge
ATM OCN 100 Summer C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges –Standard rain gauge;
ATM OCN 100 Summer Standard Rain Gauge (right)
ATM OCN 100 Summer Standard Rain Gauge From J.M. Moran & WES Project of AMS
ATM OCN 100 Summer Collecting Funnel of a Standard Rain Gauge
ATM OCN 100 Summer Operation of Standard Rain Gauge (USA Today)
ATM OCN 100 Summer C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges –Standard rain gauge; –Tipping bucket;
ATM OCN 100 Summer Tipping Bucket Rain Gauge From J.M. Moran & WES Project of AMS
ATM OCN 100 Summer Tipping Bucket Rain Gauge (USA Today)
ATM OCN 100 Summer C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Requirements –Away from obstacles; –Only precipitation above open collector is to be measured. u Direct observation by Rain gauges –Standard rain gauge; –Tipping bucket; –Weighing bucket.
ATM OCN 100 Summer Weighing Bucket Gauge
ATM OCN 100 Summer “Rain Sensor” for NWS Automatic Weather Station
ATM OCN 100 Summer Automatic Weather Station in Snow Country
ATM OCN 100 Summer C. OBSERVATIONAL MEASUREMENTS OF PRECIPITATION u Measurement by Remote Sensors –Doppler Radar-estimated rainfall –Satellite-estimated rainfall
ATM OCN 100 Summer Measuring Rain with Weather Radar
ATM OCN 100 Summer Recent National Radar (Reflectivity Mode)
ATM OCN 100 Summer Doppler Radar Estimated Rainfall (in inches) for storm
ATM OCN 100 Summer Recent National Radar (Reflectivity Mode)
ATM OCN 100 Summer Doppler Radar Estimated Rainfall (in inches) for storm From 0700 CDT Monday 15 Jul 2002 to 0931 CDT Wed 15 Jul 2002
ATM OCN 100 Summer
70 Radar Estimated Rainfall [inches] from TS Allison in Houston, TX
ATM OCN 100 Summer Satellite-Derived Precipitation u Tropical Rainfall Measuring Mission (TRMM) –Precipitation radar –Microwave Imager –Visible and Infrared Scanner
ATM OCN 100 Summer Satellite-Derived Precipitation TRMM (Tropical Rainfall Measurement Mission)
ATM OCN 100 Summer Satellite-Derived Precipitation TRMM (Tropical Rainfall Measurement Mission)
ATM OCN 100 Summer How Deep is the Snow?
ATM OCN 100 Summer Snow Measurements u Snowfall –A snow board u Snowfall –Melt snow in rain gauge u Snow cover –A ruler
ATM OCN 100 Summer This Deep !
ATM OCN 100 Summer D. BUILDING A RAINDROP u Requirements for Raindrop Formation “Not all clouds precipitate!” –Build a drop that will fall; –Rain drop must be made rapidly. u The beginning –Cloud droplet formation - Nucleation (Birth) –Plenty of small cloud droplets r cloud = 20 m
ATM OCN 100 Summer A RAINDROP u A MYTH From “Bad Rain” - Alistair B. Fraser
ATM OCN 100 Summer A RAINDROP u A MYTH u But…
ATM OCN 100 Summer D. BUILDING A RAINDROP (con’t.) u Terminal velocity –Maximum speed attained by a falling object; –Caused by frictional drag from air; –Related to the mass to surface area ratio; –Hence, dependent upon cloud droplet size.
ATM OCN 100 Summer
82 D. BUILDING A RAINDROP (con’t.) u The outcome –Typical Rain Drop Sizes (2 - 4 mm. diameter) u Factors opposing Precipitation –Cloud-producing updrafts greater than droplet’s terminal velocity; –Dry atmosphere below cloud base may evaporate droplet to form VIRGA. where...
ATM OCN 100 Summer D. BUILDING A RAINDROP (con’t.) u Terminal velocity –Dependent upon size u Amount of water needed depends upon: –Volume of spherical droplet; –or equivalently, the cube of the radius (Since V = 4/3 r 3, where r = radius).
ATM OCN 100 Summer D. BUILDING A RAINDROP (con’t.) So if r cloud = 20 m, an increase to r rain = 200 m: –then a tenfold increase in radius (200 m Vs. 20 m ) causes a Volume increase that would be 10 3 = 1000 times larger.
ATM OCN 100 Summer D. BUILDING A RAINDROP (con’t.) u Requirements –Need to build Rain Drop from Cloud Droplet –But… amount of water needed is proportional to the cube of the radius! u Factors opposing Precipitation –Cloud-producing updrafts greater than droplet’s terminal velocity; –Dry atmosphere below cloud base may evaporate droplet to form VIRGA. where...
ATM OCN 100 Summer D. BUILDING A RAINDROP (con’t.) u Factors opposing Precipitation –Cloud-producing updrafts greater than droplet’s terminal velocity; –Dry atmosphere below cloud base may evaporate droplet to form VIRGA.
ATM OCN 100 Summer Virga
88 A Convective Rainshower
ATM OCN 100 Summer E. POSSIBLE PRECIPITATION MECHANISMS (Growth of Liquid rain drops) u The current proposed mechanisms: –Simple Condensation by Diffusion Process –The Collision - Coalescence Process –The Ice Crystal or Bergeron-Findeisen Process or specifically,... or specifically,...
ATM OCN 100 Summer PRECIPITATION MECHANISM: CONDENSATION-DIFFUSION PROCESS u Based upon H 2 0 vapor molecules condensing upon cloud droplets; u Competing Effects –Curvature Effect –Solute Effect u Condensation needs to overcome surface tension of droplet; u Process would take 24 to 48 hours; u Hence, process is too slow!
ATM OCN 100 Summer PRECIPITATION MECHANISM: COLLISION-COALESCENCE PROCESS Requires droplets of various sizes, with some greater than 20 m diameter; u Large droplets have greater fall speed; Figure 8.2 Moran & Morgan (1997)
ATM OCN 100 Summer COLLISION-COALESCENCE THEORY (con’t.) u Different sized droplets have different surface electrostatic charges; u Large droplet has a wake “low”; u Thus, large droplets collect smaller droplets and form a rain drop.
ATM OCN 100 Summer PRECIPITATION MECHANISM: ICE CRYSTAL ( or Bergeron-Findeisen) PROCESS u Requires a mixture of ice crystals and supercooled liquid droplets; –supercooled droplet remains a liquid at -40 o C (-40 o F) < T < 0 o C (32 o F); –smaller droplets are more frequently supercooled.
ATM OCN 100 Summer Saturation Vapor Pressure as a Function of Temperature See Fig. 6.3 Moran & Morgan, 1997
ATM OCN 100 Summer
96 ICE CRYSTAL THEORY (con’t.) u Saturation vapor pressure over supercooled liquid >> over ice at same T; u Therefore, ice crystal grows at expense of supercooled water droplet. Figure 8.3 Moran & Morgan (1997)
ATM OCN 100 Summer F. PRECIPITATION TYPES u Distinguishing Features of Precipitation Types –Liquid (Rain, Drizzle) –Frozen (Snow, Ice Pellets, Hail) –Freezing (Freezing Rain, Freezing Drizzle) where --
ATM OCN 100 Summer LIQUID PRECIPITATION National Weather Service
ATM OCN 100 Summer FROZEN PRECIPITATION National Weather Service
ATM OCN 100 Summer Snow
101 Recall PHYSICAL PHASES of H 2 O u Solid (Ice) -- Note Hexagonal (6 sided) Structure
ATM OCN 100 Summer Varieties of Snowflakes
ATM OCN 100 Summer Varieties of Snowflakes (USA Today) See Fig. 8.6, Moran & Morgan, 1997
ATM OCN 100 Summer Varieties of Snowflakes See Fig. 8.6, Moran & Morgan, 1997
ATM OCN 100 Summer FREEZING PRECIPITATION National Weather Service
ATM OCN 100 Summer Freezing Rain
ATM OCN 100 Summer Freezing Rain/Ice Storm
ATM OCN 100 Summer Hail Stones
ATM OCN 100 Summer Hail Stones
ATM OCN 100 Summer Hail Storm
ATM OCN 100 Summer Snow Event
ATM OCN 100 Summer Rain Event
ATM OCN 100 Summer Freezing Rain Event
ATM OCN 100 Summer Ice Pellet (Sleet) Formation
ATM OCN 100 Summer Summary of Precipitation Type Formation
ATM OCN 100 Summer Freezing Rain Climatology
ATM OCN 100 Summer G. PRECIPITATION CLIMATOLOGY - Annual
ATM OCN 100 Summer G. PRECIPITATION CLIMATOLOGY - July
ATM OCN 100 Summer G. PRECIPITATION CLIMATOLOGY - January
ATM OCN 100 Summer H. WEATHER MODIFICATION BACKGROUND u Statement of Problem –Why no precipitation? –Can humans cause rain? u For precipitation, need: –sufficient atmospheric humidity; –a cloud; –sufficiently large raindrops/snowflakes to fall & reach ground as rain or snow.
ATM OCN 100 Summer INTENTIONAL ARTIFICIAL WEATHER MODIFICATION u Goals –Stimulate Precipitation –Dissipate Clouds & Fog –Suppress Hail –Modify Hurricanes
ATM OCN 100 Summer C. WEATHER MODIFICATION (con’t.) u Precipitation Stimulation Techniques - "Cloud seeding" –Early Weather Modification Techniques –Modern Precipitation Stimulation Strategies –Problems F Scientific F Legal
ATM OCN 100 Summer TYPICAL STRATEGIES u WARM CLOUDS –Add large hygroscopic nuclei. u COLD CLOUDS –Freeze all supercooled droplets with Dry Ice (Solid CO 2 ); –Add freezing nuclei with ice-like crystal structure with Silver Iodide (AgI).
ATM OCN 100 Summer ATM OCN Summer 2001 LECTURE 13 (Con’t.) PRECIPITATION & the PRECIPITATION FORMATION PROCESS A. Introduction B. Background C. Observations & Measurements D. Building a Raindrop E. Possible Precipitation Mechanisms F. Precipitation Types G. Precipitation Climatology H. Artificial Weather Modification