Transcript Weather Variables

• WEATHER - DAILY CHANGES IN THE
EARTH’S ATMOSPHERE
• CLIMATE - LONG-TERM,
SYSTEMATIC CHANGES IN THE
EARTH’S CLIMATE OF A MULTI-YEAR
SCALE
WEATHER VARIABLES
- PRESSURE
- TEMPERATURE
- DEW POINT
- HUMIDITY
- WIND SPEED / DIRECTION
- CLOUD COVER
• PRESSURE IS THE
FORCE IN WHICH THE
ATMOSPHERE ABOVE
YOU EXHURTS ON YOU
*2
*3
• UNITS FOR MEASURING PRESSURE
*1
*6
• PRESSURE
DECREASES
AS ALTITUDE
INCREASES
*1
• PRESSURE GRADIENTS (OR VARIATIONS
IN PRESSURE) CAUSE THE WIND TO BLOW
FROM HIGH PRESSURE TO LOW
PRESSURE AREAS
*1
HEAT IN THE ATMOSPHERE
TEMPERATURE
IS THE
MEASUREMENT
OF THE HEAT
ENERGY IN THE
AIR
*7
HEAT IN THE ATMOSPHERE
WATER VAPOR
INFLUENCES
MUCH OF THE
ATMOSPHERE’S
ENERGY,
ESPECIALLY
DURING PHASE
CHANGES
*6
HEAT ENERGY VOCABULARY
HEAT OF FUSION – ENERGY REQUIRED TO
CHANGE 1 GRAM FROM SOLID TO LIQUID
HEAT OF VAPORIZATION – ENERGY
REQUIRED TO CHANGE 1 GRAM FROM
LIQUID TO GAS
*6
HEAT ENERGY VOCABULARY
HEAT OF FUSION
WATER = 80 CALORIES/GRAM
HEAT OF VAPORIZATION
WATER = 540 CALORIES/GRAM
*6
HEAT ENERGY VOCABULARY
*6
SPECIFIC HEAT OF WATER
WATER REQUIRES
MORE ENERGY
THAN MOST
MATERIALS TO
RAISE ITS
TEMPERATURE
BEFCAUSE IT
HAS A HIGH
SPECIFIC HEAT
*6
THE AMOUNT OF WATER VAPOR IN THE AIR
ABSOLUTE HUMIDITY – THE WEIGHT OF THE
WATER VAPOR IN A VOLUME OF AIR
RELATIVE HUMIDITY – THE PERCENTAGE OF
WATER VAPOR IN THE SURROUND AIR
THE AMOUNT OF WATER VAPOR IN THE AIR
*8
CONDENSATION OF WATER
DEW POINT- THE
TEMPERATURE
AT WHICH AN
AMOUNT OF
WATER VAPOR
WILL BEGIN TO
CONDENSE FROM
A GAS TO A
LIQUID STATE
*9
CONDENSATION OF WATER
SATURATED – REACHED THE MAXIMUM
POTENTIAL HOLDING CAPACITY
UNSATURATED – HAVING THE ABILITY TO
ABSORB MORE VAPOR
CONDENSATION OF WATER
THE HIGHER THE TEMPERATURE, THE
MORE WATER VAPOR THAT CAN BE
HELD IN THE SURROUNDING AIR
PSYCHROMETER
A PSYCHROMETER
MEASURES
HUMIDITY AND
DEWPOINT BY
MEASURING THE
CURRENT AIR
TEMPERATURE
COMPARED TO THE
SATURATED AIR
TEMPERATURE
*10
Psychromotor
Dry Bulb Temperature
•
The Dry Bulb temperature, usually referred to as air temperature, is the air property that is most common
used.
•
When people refer to the temperature of the air, they are normally referring to its dry bulb temperature.
Wet Bulb Temperature
•
The Wet Bulb temperature is the temperature of complete saturation. This is the temperature indicated by
a moistened thermometer bulb exposed to the air flow.
•
Wet Bulb temperature can be measured by using a thermometer with the bulb wrapped in wet muslin.
•
The rate of evaporation from the wet bandage on the bulb, and the temperature difference between the dry
bulb and wet bulb, depends on the humidity of the air. The evaporation is reduced when the air contains
more water vapor.
•
The wet bulb temperature is always lower than the dry bulb temperature but will be identical with 100%
relative humidity (the air is at the saturation line).
Combining the dry bulb and wet bulb temperature in a psychrometric
diagram or Mollier chart, gives the state of the humid air. Lines of
constant wet bulb temperatures run diagonally from the upper left to the
lower right in the Psychrometric Chart.
http://www.kwangu.com/work/psychrometric.htm
CONVECTION
CONVECTION
CREATES RISING
AIR CURRENTS
THROUGH LESS
DENSE (WARMER)
AIR RISING OVER
THE MORE DENSE
(COLDER) AIR
*11
HARRIS HILL, NEW YORK
*11
CONDENSATION OF WATER
CLOUDS FORM WHEN RISING AIR COOLS
(AS IT EXPANDS) WHICH CAUSES THE AIR
THE AIR TEMPERATURE TO FALL TO ITS
DEW POINT.
STRATUS CLOUDS
*12
CUMULUS CLOUDS
*12
CIRRUS CLOUDS
*12
CONDENSATION OF WATER
http://www.youtube.com/watch?v=vPC5i6w3yDI
&feature=related
Isotherms
• Isotherms are lines of constant or equal temperature.
• They are often used on weather maps by meteorologists to give a large
scale view of temperatures across the U.S.
•
If you have ever looked at a weather map in a newspaper, the
isotherms are used to divide the color-filled temperatures
•
•
For example, in the map below, temperatures in the 60's may be represented
by a yellow color, while temperatures in the 70's may be represented by an
orange color.
The line that divides the yellow from the orange is the isotherm. All of the
locations between the 60 degree isotherm and the 70 degree isotherm will have
a temperature between 60 and 70 degrees.
Isobars
• Isobars are lines of constant or equal pressure on a weather map.
• They can be used to find areas of low or high pressure over a broad
area (like the U.S.), and they can tell us how intense the system may
be.
•
On weather maps, you may have noticed areas that have a large “L” or
“H” over a region with lines circling around them. The lines circling
them are isobars
•
Generally the lowest pressure is where precipitation is most likely to
fall, and high pressures are usually associated with clear and sunny
conditions. Where the isobars are close together, windy conditions may
be expected. Elongated areas of low pressure on surface and upper air
weather maps are called "troughs" and elongated areas of high pressure
are called "ridges."
So why do we use isotherms and isobars?
• Isotherms and isobars allow us to view large scale processes much
more easily than looking at the raw data from individual weather
stations itself.
Figure C: Raw Data
Figure D: Isotherms Added