3 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 groundThe cooling air may then become saturatedMoisture can condense out as droplets on the surface
4 Dew and Frost This process is aided by the surface itself This provides something for the moisture to condense ontoRough surfaces are betterCondensation likes rough surfacesRough surfaces prevent too much air flowVegetation gets more dew as it is a source of moisture (air will have higher humidity)
7 Formation of Dew & Frost Figure 6.2Figure 6.1As 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.
8 Fog and DewMost common on clear nights when there are no clouds to reflect (or absorb and re-radiate) the energy emitted by the Earth’s surfaceNeed a source of moisture which is then cooled
10 Cloud Groups & TypesClouds 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.
11 Cloud ClassificationClassification is based on appearance and the altitudeof the clouds. The original classification schemeconsisted of four categories:Sheet-like Stratus “Layer”Puffy Clouds Cumulus “Heap”Wispy Clouds Cirrus “Curl of Hair”Rain Clouds Nimbus “Rain”
12 High Clouds 1. High Clouds - Cirrus (Ci) - Cirrostratus (Cs) Late in the 1800’s, the classification system was expandedto include more descriptive terms. Today there are fourmajor cloud groups.1. High Clouds- Cirrus (Ci)- Cirrostratus (Cs)- Cirrocumulus (Cc)High clouds are usually above 6000m and consist primarilyof ice crystals. They are blown by the upper level winds andare responsible for haloes and sundogs, etc.
13 Cirrus CloudsHigh clouds (above 6000 m in middle latitudes) that are thin and wispy and comprised mostly of ice crystals.Figure 6.9
14 Cirrocumulus CloudsHigh clouds that are rounded puffs, possibly in rows, are less common than cirrus.Figure 6.10
15 Cirrostratus CloudsHigh clouds that thinly cover the entire sky with ice crystals.Light passing through these crystals may form a halo.Figure 6.11
16 Middle Clouds 2. Middle Clouds - Altostratus (As) - Altocumulus (Ac) Middle clouds are usually between 2000m and 6000m andconsist primarily of water droplets. The sun can still be seenthrough altostratus although there is no halo.
17 Altocumulus CloudsMiddle 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
18 Altostratus CloudsMiddle clouds that cover the entire sky and may create a dimly visible or watery sun and diminish formation of shadows.Figure 6.13
19 Low Clouds 3. Low Clouds - Stratus (St) - Stratocumulus (Sc) - Nimbostatus (Ns)Low clouds are usually below 2000m and consist primarilyof water droplets. The sun cannot be seen through stratus clouds.
20 Nimbostratus CloudLow clouds (below 2000m) with precipitation that reaches the ground.Shredded parts of these clouds are called stratus fractus or scud.Figure 6.14
21 Stratocumulus CloudsFigure 6.15Low 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.
22 Stratus CloudsFigure 6.16Low clouds that resemble a fog, but do not reach the ground, and can generate a light mist or drizzle.
23 Clouds With Vertical Development - Cumulus (Cu)- Cumulonimbus (Cb)
24 Cumulus Humilis Clouds Figure 6.17Clouds with vertical development that take a variety of shapes, separated by sinking air and blue sky.Shredded sections are called cumulus fractus.
25 Cumulus Congestus Clouds Figure 6.18Clouds with vertical development that become larger in height, with tops taking a ragged shape similar to cauliflower.
26 Cumulonimbus CloudFigure 6.18Clouds with vertical development that have grown into a towering thunderstorm cloud with a variety of key features, including the anvil top.