| NATS 101-05 Lecture 8 |
| Condensation, Fog and Clouds |
| Cloud Condensation Nuclei |
| Small, airborne particles are necessary on which water vapor can condense to produce cloud droplets | |
| Without such particles, RH>100% would be needed to produce clouds | |
| Such surfaces are called Cloud Condensation Nuclei (CCN) | |
| CCN are light and stay suspended for days |
| Cloud Condensation Nuclei |
| Sources | |
| Dust, volcanic ash, smoke, soot, salt, sulfate particles | |
| Concentrations | |
| 1,000-10,000 per cc Highest over cities Highest at surface |
| Size of Cloud Droplets |
| What is Fog? |
| Fog - a cloud at the ground | |
| There are four basic types of fog | |
| Radiation (and Valley) Fog | |
| Advection Fog | |
| Upslope Fog | |
| Steam Fog | |
| Combinations exist (Radiation-Advection) |
| Radiation or Ground Fog |
| Valley Fog |
| Radiation Fog in Valley |
| Fog Dissipation in the Morning |
| Advection Fog |
| Advection Fog at Golden Gate |
| Upslope Fog |
| Steam Fog or Sea Smoke |
| Why You See Your Breath on a Cold Winter Night |
| Condensation can occur if moist, warm air mixes with cold, dry air. | |
| Temp RH SVP VP | |
| Air 0oC 20% 6 mb 1 mb | |
| (clear) | |
| Breath 36oC 80% 63 mb 55 mb | |
| (clear) | |
| 50-50 18oC 140% 20 mb 28 mb (cloud) | |
| 90-10 4oC 90% 8 mb 6 mb | |
| (clear) | |
| The 50-50 mix condenses into a cloud that quickly evaporates as your exhalation is diluted further |
| Steam Fog over Thermal Pool |
| Precipitation or Frontal Fog |
| Number of Days with Fog |
| Summary: Condensation |
| Condensation | |
| Can occur by cooling or moistening of air | |
| CCN permit condensation at RH near 100% | |
| Small (<0.2 to 1 microns) airborne particles | |
| Responsible for Haze formation at RH < 100% |
| Summary: Fog |
| Fog - a cloud at the ground | |
| Composed of small (20 micron) water drops | |
| Four primary types of Fog | |
| Radiation-Advection-Upslope-Steam | |
| Occur under distinct weather conditions |
| Cloud Classification |
| A morphological classification scheme developed by Luke Howard (1803) | |
| Latin words used to describe different cloud types as they appear to observer on the ground | |
| Four basic cloud types and combinations | |
| stratus - sheet-like clouds (layer) | |
| cumulus - puffy clouds (heap) | |
| cirrus - wispy clouds (curl of hair) | |
| nimbus - rain clouds (violent rain) |
| Cloud Classification |
| Height grouping modification of Howard scheme (Abercromby and Hildebrandsson, 1887) | |
| Still used today | |
| Ten principle cloud forms | |
| High - Middle - Low - Vertical Development |
| Slide 22 |
| Cloud Classification |
| Other cloud types | |
| Lenticular - stacks like saucers above and downwind of mountains (lens-shaped) | |
| Banner - cloud at top and immediately downwind of mountain peaks | |
| Mammatus - pendulous undulations that occur underneath some thunderstorm anvils (breast) | |
| Pileus - cloud situated just above the top of a thunderstorm top (hat) |
| Cloud Classification |
| Other cloud types | |
| Kelvin-Helmholtz - billowed clouds that resemble breaking waves and form in strong wind shear | |
| Nacreous - thin, sometimes iridescent clouds in stratosphere (30 km height) (mother of pearl) | |
| Noctilucent - thin clouds in upper mesosphere (80 km height), seen in polar twilight (night-light) |
| Cirrus (Ci) |
| Cirrocumulus (Cc) |
| Cirrostratus (Cs) |
| Altocumulus (Ac) |
| Altostratus (As) |
| Nimbostatus (Ns) |
| Stratus (St) |
| Stratocumulus (Sc) |
| Cumulus (Cu) Humilis |
| Cumulus Congestus (Cu) |
| Cumulonimbus (Cb) |
| Supercell Cb |
| Mammatus |
| Pileus |
| Lenticular |
| Lenticular with Rotor |
| Banner Cloud |
| Kelvin-Helmholtz |
| Jet Contrail |
| Summary: Cloud Classification |
| Next Lecture Assignments |
| Topic - Cloud Formation and Types, vertical stability | |
| Reading - Ahrens pages 89-105, 109-118 | |
| Problems - 4.3, 4.13 - 4.16, 5.1, 2, 3, 4, 5, 7 |