Dew and Frost Today Dew Frost Clouds

Condensation nucleus demonstration

Dew and Frost At night the ground cools by radiation. The air in a thin layer in contact with the ground cools as it loses heat to the ground The cooling air may then become saturated Moisture can condense out as droplets on the surface

Dew and Frost This process is aided by the surface itself This provides something for the moisture to condense onto Rough surfaces are better Condensation likes rough surfaces Rough surfaces prevent too much air flow Vegetation gets more dew as it is a source of moisture (air will have higher humidity)

Dew and Frost Types

Rime

Formation of Dew & Frost Figure 6.2 Figure 6.1 As air cools to its saturation, or dew point, vapor molecules slow down and can adhere as dew on the ground surface or as frost when air temperature drops below freezing. Daily temperature lows often occur by radiational cooling, forming dew at night or early morning.

Fog and Dew Most common on clear nights when there are no clouds to reflect (or absorb and re-radiate) the energy emitted by the Earth’s surface Need a source of moisture which is then cooled

CLOUDS

Cloud Groups & Types Clouds are water droplets or ice crystals (or a mixture of the two) suspended in the atmosphere. Clouds are grouped by their elevation as high, middle, low, and those that vertically stretch across many altitudes. There are several cloud types in these 4 groups.

Cloud Classification Classification is based on appearance and the altitude of the clouds. The original classification scheme consisted of four categories: Sheet-like Stratus “Layer” Puffy Clouds Cumulus “Heap” Wispy Clouds Cirrus “Curl of Hair” Rain Clouds Nimbus “Rain”

High Clouds 1. High Clouds - Cirrus (Ci) - Cirrostratus (Cs) Late in the 1800’s, the classification system was expanded to include more descriptive terms. Today there are four major cloud groups. 1. High Clouds - Cirrus (Ci) - Cirrostratus (Cs) - Cirrocumulus (Cc) High clouds are usually above 6000m and consist primarily of ice crystals. They are blown by the upper level winds and are responsible for haloes and sundogs, etc.

Cirrus Clouds High clouds (above 6000 m in middle latitudes) that are thin and wispy and comprised mostly of ice crystals. Figure 6.9

Cirrocumulus Clouds High clouds that are rounded puffs, possibly in rows, are less common than cirrus. Figure 6.10

Cirrostratus Clouds High clouds that thinly cover the entire sky with ice crystals. Light passing through these crystals may form a halo. Figure 6.11

Middle Clouds 2. Middle Clouds - Altostratus (As) - Altocumulus (Ac) Middle clouds are usually between 2000m and 6000m and consist primarily of water droplets. The sun can still be seen through altostratus although there is no halo.

Altocumulus Clouds Middle clouds (between 2000 and 6000m in middle latitudes) that are puffy masses of white with gray edges. With your hand overhead, they are about the size of your fingernail. Figure 6.12

Altostratus Clouds Middle clouds that cover the entire sky and may create a dimly visible or watery sun and diminish formation of shadows. Figure 6.13

Low Clouds 3. Low Clouds - Stratus (St) - Stratocumulus (Sc) - Nimbostatus (Ns) Low clouds are usually below 2000m and consist primarily of water droplets. The sun cannot be seen through stratus clouds.

Nimbostratus Cloud Low clouds (below 2000m) with precipitation that reaches the ground. Shredded parts of these clouds are called stratus fractus or scud. Figure 6.14

Stratocumulus Clouds Figure 6.15 Low clouds with rounded patches that range in color from light to dark gray. With your hand extended overhead, they are about the size of your palm and cover most of the sky.

Stratus Clouds Figure 6.16 Low clouds that resemble a fog, but do not reach the ground, and can generate a light mist or drizzle.

Clouds With Vertical Development - Cumulus (Cu) - Cumulonimbus (Cb)

Cumulus Humilis Clouds Figure 6.17 Clouds with vertical development that take a variety of shapes, separated by sinking air and blue sky. Shredded sections are called cumulus fractus.

Cumulus Congestus Clouds Figure 6.18 Clouds with vertical development that become larger in height, with tops taking a ragged shape similar to cauliflower.

Cumulonimbus Cloud Figure 6.18 Clouds with vertical development that have grown into a towering thunderstorm cloud with a variety of key features, including the anvil top.

Summary of Cloud Types Figure 6.20