Course 5 - Section 10 - Synoptic Features Flashcards
Two basic cloud forms1
Stratiform
appear in horizontal layers. They often have very small vertical motions associated with them and they can cover a large area
Cumuliform
Have a more prominent vertical formation and usually do not cover a very large area. They are the result of rising air currents and have significant updrafts and downdrafts
Cumuliform clouds are of particular interest to pilots and ATS personnel due to their impact on flying conditions.
Weather phenomena associated with cumuliform clouds can include precipitation, icing, high wind, turbulence, poor visibility, and runway contamination
weather associated with cumuliform clouds can even cause structural damage to aircraft and aviation infrastructure
List the four types of cumuliform clouds
Cumulus (CU)
Towering cumulus (TCU)
Cumulonimbus (CB)
Altocumulus castellanus (ACC)
Cumulus (CU) clouds
Develop vertically in the form of rising mounds, domes or towers
Have a bulging upper part
appear detached from other clouds
Are generally dense with sharp or ragged outlines
Are mostly brilliant white at the top and their bases are relatively dark and nearly horizontal
GET PROGRESSIVELY LARGER AND POTENTIALLY MORE SEVERE AS THE VERTICAL UPDRAFTS AND DOWNDRAFTS GROW
Towering Cumulus (TCU) clouds
Towering cumulus (TCU) clouds are also known as cumulus congestus
TCUs are made of a rapidly growing cumulus or individual dome shaped cloud. The height of TCU exceeds the width
THE DISTINCTIVE CAULIFLOWER TOP OF A TCU OFTEN MEANS SHOWERS BELOW
GET PROGRESSIVELY LARGER AND POTENTIALLY MORE SEVERE AS THE VERTICAL UPDRAFTS AND DOWNDRAFTS GROW
Cumulonimbus (CB) clouds
Cumulonimbus (CB) clouds are thunderclouds. THEY CONTAIN THUNDERSTORM ACTIVITY
They appear heave and dense with a considerable vertical extent in the form of a mountain or huge tower.
At least part of a CB’s upper portion is smooth, fibrous or striated, and nearly always flattened; this part often spreads out in the shape of an anvil or a vast plume
Low ragged clouds frequently occur under the base of CBs. These clouds may or may not merge with the base of the CB
CBs can attain heights of more than 70 000 feet, however, most CBs in Canada average about 39 000 feet. THESE CLOUDS RESULT IN SIGNIFICANT ICING AND TURBULENCE AND ARE OFTEN A FACTOR IN WEATHER RELATED AIRCRAFT ACCIDENTS
GET PROGRESSIVELY LARGER AND POTENTIALLY MORE SEVERE AS THE VERTICAL UPDRAFTS AND DOWNDRAFTS GROW
Altocumulus Castellanus (ACC) clouds
Altocumulus castellanus (ACC) clouds are white, grey or both white and grey. They contain patches, sheets, or layers of cloud generally with shading
ACCs are composed of laminae, rounded masses and rolls, which are sometimes partly fibrous or diffuse and which may or may not be merged
Most of the regularly arranged small elements have an apparent width of between one and five degrees
ACCs display vertical growth and are the result of mid-level instability which is defined as the up and down movement of air in the middle levels of the atmostphere.
ACCs ARE OFTEN A TELLTALE SIGN OF IMPENDING THUNDERSTORM DEVELOPMENT
Name the types of pressure systems
High pressure
Low pressure
troughs
ridges
High Pressure Areas
A high pressure area is a region where the atmospheric pressure is greater than its surrounding environment, with pressure values increasing towards the centre. It can cover hundreds to thousands of square km
A high pressure area may also be called a high or an anticyclone
On surface weather maps, highs are labelled H
AIR CIRCULATES CLOCKWISE AROUND THE CENTRE OF HIGH PRESSURE SYSTEMS
Low Pressure Areas
A low pressure area is a region where the atmospheric pressure is lower than the surrounding environment, with pressure values decreasing towards the centre. Its diameter can range from ten to hundreds of km
A low pressure area may also be called a low, a cyclone, or a depression
On surface weather maps, lows are labelled L
AIR CIRCULATES COUNTER CLOCKWISE AROUND THE CENTRE OF LOW-PRESSURE SYSTEMS
Troughs
Low pressure systems are often not a perfect circle. Their shape may include arms that extend from their centre. Those arms are called troughs
A trough is essentially an elongated region of relatively low atmospheric pressure, often associated with fronts
Ridges
high pressure systems can also have arms that extend from their centre. These are called ridges
A ridge is essentially an elongated region of relatively high atmospheric pressure
Isobars
Pressure systems are represented on weather maps using isobars
isobars are curved lines that connect points of equal pressure and show variations in pressure at any given time
Specifically, isobars join lines of equal mean sea level pressure (MSLP) and form pressure patterns that outline or enclose high and low pressure areas
- measured in hectopascals (hPa)
- analyzed on meteorological charts
- used to identify high and low pressure systems
- SPACED EVERY 4 hPa above and below 1000 hPa
Pressure Gradient
Pressure gradient is the rate of change of pressure with horizontal distance measured in kilometers
The speed of wind is directly proportional to the pressure gradient. The faster the pressure changes, the stronger the wind will be.
The difference in pressure between isobars is always 4 hPA, while the horizontal spacing or the distance in kilometers between the isobars varies
weak vs steep pressure gradient
How are pressure gradients calculated?
Pressure gradients are always calculated at 4 hPa in “X” kilometers, where “X” is the distance between two consecutive isobars
Steep Pressure Gradient
Isobars are close or crowded together
A low is termed “Deep”
A high is termed “Strong”
Weak pressure gradient
Isobars are far apart
A low is termed “shallow”
A high is termed “weak”
Coriolis force
The coriolis force is caused by the earth’s rotation. In the northern hemisphere, as the air moves from a high pressure area to a low pressure area, the coriolis force deflects moving air to the right.
This is because the earth rotates counter clockwise if you are standing on its surface in the northern hemisphere
The coriolis force does not cause wind; it affects the direction of air movement. Affected air flows parallel to the isobars. If the earth didn’t rotate, wind would flow directly from a high to a low pressure area
Buys Ballots Law
In the northern hemisphere, the pressure gradient force and coriolis force combine to cause air to flow parallel to the isobars, clockwise around a high, counter clock wise around a low
With the wind at your back in the northern hemisphere the area of low pressure lies to your left
veering and backing
veering: wind makes a clockwise change in direction
backing: wind makes a counter clockwise change in direction