10/3/2011 Forms of Cloud Formation Condensation v Clouds v Visible aggregate of minute droplets of water (ice) and v Form as a result of adiabatic cooling v Lifted condensation level Precipitation v Cooled to dew point v Air is saturated Chapter 5 v Needs surface to condense to v Condensation nuclei v Dust, smoke, salt Growth of Clouds Cloud Classification v Condensation nuclei v Cirrus v Hygroscopic v High, white, thin v Effective particles for condensation v Wispy, feathery, curly v Salt, dust, ash, pollen v Cumulus v Hydrophobic v Flat base, rising domes, towers v Not effective particles for condensation v Examples? v Stratus v Sheets, layers v A billion cloud droplets equal one rain drop Cloud Classification Cloud Classification v High v High v Above 6000m v Above 6000m v Composed of ice crystals v Indicate stormy weather coming v Middle v Cirrus v 2000 – 6000m v Form hooks (mares tails) v Cirrostratus v Low v Transparent v Below 2000m v Cover much of the sky v Vertical development v Cirrocumulus v Patches v 2000-6000m v Mackerel sky 1 10/3/2011 Cloud Classification Cloud Classification v Middle v Low v 2000 - 6000m v Below 2000m v Prefix - alto v Stratus v Uniform v Altocumulus v Covers sky v Larger patches v Light precip v Altostratus v Stratocumulus v Formless v Combo of v Grayish v stratus and cumulus v May produce v Nimbostratus v Rain or snow v Nimbus = Rain or snow v Stable Air Cloud Classification Cloud Classification v Vertical Development v 2000 - 6000m v Associated with unstable air v Cumulus v White, puffy v Clear days v Fair weather clouds v Cumulonimbus v Huge towers v Dark, dense v Top = anvil v Thunderstorms Mammatus Types of Fog Types of Fog v Fog v Fog from cooling v Radiation Fog v A cloud with its base or very near the ground v Ground radiates heat v Form from v Ground and air cool rapidly v Cooling v Clear skies and high rel. hum. v Radiation Fog v How thick depends on wind v Advection Fog v Little to no wind v Thin and low to ground v Upslope Fog v Slightly more wind v Thicker and higher up v Evaporation v Thicker in valleys v Cold and dense v Addition of water vapor v Lifting (Not really) v Steam Fog v Ground warms up v Frontal (precip) Fog v Fog dissipates 2 10/3/2011 Types of Fog Types of Fog v Fog from cooling v Fog from cooling v Advection Fog v Upslope Fog v Air moving horizontally v Humid air moves over slope v Warm moist air v Air expands and cools (adiabatically) v Blown over cool surface v Heat loss to surface v Air cools to dew point v Dense v 300 - 600m deep Types of Fog Types of Fog v Fog from evaporation v Fog from evaporation v Steam Fog v Frontal Fog v Cool air moves over warm water v Frontal wedge v Warm water evaporating v Warm air get lifted over cold v Saturates cool air v Rain v Rain evaporates v Cool air becomes saturated Dew and Frost Dew and Frost v Dew v White frost v Condensation of water vapor on objects v Not frozen dew v Cooler objects v Dew point below freezing v Grass is common because of transpiration increasing the v Deposition relative humidity of the air v Water vapor directly to solid 3 10/3/2011 How Precipitation Forms How Precipitation Forms v Cloud droplets v Cloud droplets v Very tiny (.02 mm) v Don’t freeze at 0oC v Supercooled water v Raindrop v Freeze on contact v 2 mm v Freezing nuclei v -10 to -20oC v Mix ice and water v -20oC v All ice How Precipitation Forms How Precipitation Forms v Bergeron Process v The Collision-Coalescence v Ice crystals have lower vapor pressure than liquid droplets v Liquid droplets fall through cloud v More evaporation from liquid droplets v Collect other cloud droplets v Droplet gets bigger (a) v Raises rel. humid. (already 100%) v Bottom flattens out (b) v Supersaturated v Depression (c) v Ice crystals collect more water v At 5 mm raindrop breaks apart v Ice crystals grow larger v Numerous small drops (d) v Rapid growth v Repeats process v Large snowflakes v 10 - 30 ice crystals Forms of Precipitation Forms of Precipitation v Rain v Rain v Snow v .5 - 5 mm v Sleet v Glaze v Drizzle v Hail v .05 to .5 mm v Rime v Mist v Graupel v .005 to .05 mm v Most precip. starts as snow and melts on the way v Precip can evap. before reaching the ground v Produces virga v Rain streaks don’t reach the surface 4 10/3/2011 Forms of Precipitation Forms of Precipitation v Snow v Sleet v Aggregate of ice crystals v Particles of ice v Low temp. v Light fluffy snow v High temp. v Heavy wet snow v Snowballs Forms of Precipitation Forms of Precipitation v Glaze v Hail v Freezing rain v Hard round pellets v Lumps of ice v Layers inside v Form in cumulonimbus clouds v Updrafts and downdrafts v Carry hail up and down v Become larger in size Forms of Precipitation Precipitation Measurement v Rime v Standard rain gauge v Tipping-bucket gauge v Funnel water v Each bucket holds .025 cm v Formed from v Channel 1/10 of funnel v Bucket fills and dumps v Freezing of supercooled fog or v Trace of precipitation v Records measurement on graph cloud droplets v Unmeasurable v Freezes on contact with object v Weighing gauge v Weighs the fallen rain 5 10/3/2011 Precipitation Measurement Precipitation Measurement v Snow v Errors v Measure v Rain fall varies drastically v Depth v Place to place v Multiple spots v Gauges v Water equivalent v Should be far away from objects v Melt v Open fields v Measure as rain v Wind v Gauges should have windscreens v 10 inches of snow equals 1 inch of rain????? Not exactly v 30 cm of light fluffy snow ≈1 cm of rain v 4 cm of heavy wet snow ≈ 1 cm of rain Precipitation Measurement Weather Modification v Radar v Intentional Weather Modification v Sends out radio waves v Deliberate human intervention to influence atmospheric processes v Radio waves reflect off of precip. v 3 categories v Reflected signal called - echo v Energy (heat or air mixing) v Helicopter disperses fog v Changing land and water surfaces v Covering with dark substance v Absorbs solar energy v Increase in temp. v Triggering, intensifying, or redirecting v Cloud seeding v Uses dry ice Weather Modification Weather Modification v Triggering, intensifying, or redirecting v Fog and Cloud Dispersal v Cloud seeding v Dry Ice v With v Water à Ice v Dry ice v Light snow shower v Cools air v Clouds disperse v Silver iodide v Helicopters v Freezing nuclei v Strong downdrafts v Increases precip. v Dry air mixes with saturated v Must have clouds v Heat v Clouds below 0oC v Turboclair v Jet engines heat the air 6 10/3/2011 Weather Modification Weather Modification v Hail Suppression v Frost Prevention v HailStop v 2 methods v Uses sound waves v Conserve heat v Intent to disrupt hail cycle v Cover plants v Does it work????? v Add heat v Water sprinklers v Warms ice v Latent heat released when freezes v Air mixers v Mixes warm air above with cold air below v Heaters 7.