Presentation on theme: "What is Weather? Weather is the condition of the atmosphere at a certain time and place. Can you guess the atmospheric conditions at this time and place?"— Presentation transcript:
What is Weather? Weather is the condition of the atmosphere at a certain time and place. Can you guess the atmospheric conditions at this time and place?
The Water Cycle The continuous movement of water from sources on the Earth’s surface into the air and onto the land. Condensation – water vapor cools and changes from a gas to a liquid. Evaporation – liquid water changes into water vapor, a gas. Precipitation – rain, snow, sleet or hail falls from the clouds onto the Earth’s surface. Runoff – water that flows across the land and collects in rivers, streams and flows to the oceans. Groundwater – water located beneath the Earth’s surface. If it is in soil pore spaces, it is called an aquifer.
Humidity Humidity - is the amount of water vapor in the air. As the temperature of the air increases, the air’s ability to hold water also increases.
Relative Humidity Relative humidity – the amount of water vapor in the air compared with the maximum amount of water vapor that the air can hold at a certain temperature. Given as a percentage. When the air holds all the water that it can at a given temperature, we say the air is saturated. The air then has a relative humidity of 100% and would be very uncomfortable.
Why is 100% humidity uncomfortable?
How to calculate relative humidity? Actual water vapor content x 100 saturation water vapor content = relative humidity % Practice calculation: Assume 1 m 3 of air at 25 o C contains 11 g of water vapor. At this temperature the air can hold 24g/m 3 of water vapor. Calculate the relative humidity of the air.
Answer 11 g/m 3 24 g/m 3 X 100 =46%
Two Factors Affecting Relative Humidity 1.) Water vapor in the air 2.) Temperature At a constant temperature and pressure, as the amount of water vapor in the air changes, the relative humidity changes. The more water vapor in the air, the higher the relative humidity. If the amount of water vapor in the air stays the same but the temperature changes, the relative humidity changes too. Relative humidity decreases as temperature rises and increases as temperature drops.
How to Measure Relative Humidity? Psychrometer – an instrument used to measure relative humidity. Made of two thermometers. One thermometer has a cloth around it’s bulb which is moistened. This is called the “wet bulb.” The other thermometer has no cloth and is called the “dry bulb.”
The difference in the readings between the two thermometers indicates the amount of water vapor in the air according to this chart:
How does the wet bulb work? The wet bulb thermometer works differently than the dry bulb. The dry bulb just measures the surrounding air temperature. On the wet bulb, air passes over the cloth and the water in the cloth evaporates, cooling the bulb. If the humidity is low, the water in the cloth will evaporate more quickly and the temperature will drop lower. If the humidity in the surroundings is high, the water from the cloth will not evaporate as easily, and the temperature change will be smaller.
Dew Point Dew Point - the temperature at which a gas condenses into a liquid. Before a gas can condense, it must have a surface to condense upon—like the blades of grass.
Frost Frost is the solid deposition of water vapor from humid air when the temperature of the solid surface is below the freezing point of water.
CLOUDS Types and details
How Clouds Form Form when water vapor in the air condenses in to liquid drops or ice crystals. Must condense on small particles in the air (dust, pollen, etc…) Condense when vapor reaches upper levels of the troposphere and cool.
Classification of Clouds Clouds are classified into 4 main types of clouds based on their altitude and shape. The word parts of each of these 4 types are combined to create over 10 cloud names.
Cumulus Description: fluffy, cotton ball like clouds. Associated with good weather. Altitude: low to the ground (lower than 2km)
Stratus Description: Flat layered clouds that cover most of the sky. As they thicken, they may produce rain. Altitude: low
Cirrus Description: Wispy, feathery clouds made of ice crystals. Altitude: High in the sky (above 6km)
Nimbus Description: Dark grey clouds that cover the whole sky and produce rain. Altitude: Low
Can you ID this one?
The Combination Clouds Most clouds are combinations of two or more basic types. If clouds are in the mid layers (2-6km), we use the prefix alto- Altocumulus