ATMOSPHERIC MOISTUREA STUDY IN METEOROLOGY

ATMOSPHERIC MOISTURE

• AS WE KNOW, WATER IS IN THE ATMOSPHERE IN THE FORM OF VAPOR.

• WHAT YOU MAY NOT KNOW IS THAT THIS WATER CARRIES WITH IT A LOT OF ENERGY.

ATMOSPHERIC MOISTURE

• AS WATER IS HEATED, THE TEMPERATURE INCREASES UNTIL YOU REACH THE BOILING POINT.

ATMOSPHERIC MOISTURE

• AS THE WATER STARTS TO TURN TO STEAM, ITS TEMPERATURE STOPS RISING.

ATMOSPHERIC MOISTURE

• THE WATER KEEPS ABSORBING HEAT, BUT STAYS AT THE SAME TEMPERATURE.

ATMOSPHERIC MOISTURE

• WHEN ALL THE LIQUID HAS BEEN CONVERTED TO A GAS, THE TEMPERATURE STARTS TO RISE AGAIN.

ATMOSPHERIC MOISTURE

• THIS EXCESS OF STORED THERMAL ENERGY IS KNOWN AS LATENT HEAT

ATMOSPHERIC MOISTURE

• WHEN GAS RE-CONDENSES INTO A LIQUID. THIS EXTRA THERMAL ENERGY ALSO GETS RELEASED INTO THE ATMOSPHERE.

• THIS EXCESS THERMAL ENERGY IS OFTEN A CRUCIAL PART IN STORM DEVELOPMENT.

ATMOSPHERIC MOISTURE

• WHEN WATER VAPOR RE CONDENSES INTO A LIQUID. THIS EXTRA THERMAL ENERGY ALSO GETS RELEASED INTO THE ATMOSPHERE.

• THIS EXCESS THERMAL ENERGY IS OFTEN A CRUCIAL PART IN STORM DEVELOPMENT.

ATMOSPHERIC MOISTURE

• IF YOU RECALL TO TURN A LIQUID INTO A GAS THE TEMPERATURE HAS TO BE ABOVE ITS BOILING POINT.

• SO HOW DOES WATER VAPORIZE IF THE TEMPERATURE ISN’T ABOVE 212̊̊̊̊ F?

ATMOSPHERIC MOISTURE

• SIMPLE ANSWER…IT DOESN’T.

• WATER DOESN’T VAPORIZE (OR BOIL) INSTEAD IT EVAPORATES

• I KNOW, I KNOW, THERE THE SAME THING RIGHT…NOPE!

ATMOSPHERIC MOISTURE

• COMPLICATED ANSWER. THE WATER MOLECULES MOVING IN A FLUID HAVE A CERTAIN AMOUNT OF ENERGY. RANDOM OR BROWNIAN MOTION ON THE SURFACE OR INTERFACE OF THE FLUID CAUSES SOME OF THESE MOLECULES TO HAVE ENOUGH ENERGY TO ESCAPE FROM THE REST OF THE WATER.

ATMOSPHERIC MOISTURE

• AT THIS POINT THE WATER IS STILL A LIQUID, BUT THE DROPLETS ARE SMALL ENOUGH AND LIGHT ENOUGH (WITH ENOUGH ENERGY) TO BE TRANSPORTED BY THE AIR MOVEMENT.

ATMOSPHERIC MOISTURE

• TEMPERATURE GRADIENT, ATMOSPHERIC PRESSURE, RELATIVE HUMIDITY ALL HAVE AN EFFECT ON HOW FAST EVAPORATION TAKES PLACE.

• THE SAME PROCESS HAPPENS WITH SNOW, WHICH IS WHY SNOW CAN MELT OR SHRINK EVEN IF THE TEMPERATURE DOESN’T RISE ABOVE FREEZING.

ATMOSPHERIC MOISTURE

• MOISTURE IN THE AIR IS ALSO REACTING TO JOIN THE LIQUID AT ITS INTERFACE. THESE TWO PROCESSES ARE IN COMPETITION WITH EACH OTHER.

• RECALL THAT WHEN THE REACTION RATE IS BALANCED THE SYSTEM IS SAID TO HAVE REACHED EQUILIBRIUM.

ATMOSPHERIC MOISTURE

• ABSOLUTE HUMIDITY IS THE AMOUNT OF WATER VAPOR IN THE AIR.

• IT IS MEASURED IN GRAMS PER CUBIC METER AS SHOWN BELOW

ATMOSPHERIC MOISTURE

• RELATIVE HUMIDITY IS THE RATIO OF THE AMOUNT OF WATER VAPOR IN THE AIR TO THE AMOUNT OF WATER VAPOR THAT IT CAN HOLD (AT THAT TEMPERATURE AND PRESSURE)

ATMOSPHERIC MOISTURE

• BASED ON THE CURRENT ABSOLUTE HUMIDITY AND ATMOSPHERIC PRESSURE, THERE IS A TEMPERATURE AT WHICH THE AIR WILL NO LONGER BE ABLE TO HOLD THE AMOUNT OF WATER IT CURRENTLY HOLDS.

• THIS TEMPERATURE IS CALLED THE DEW POINT.

ATMOSPHERIC MOISTURE

• THERE ARE MULTIPLE WAYS TO MEASURE RELATIVE HUMIDITY.

• SOME INCLUDE USING MEMBRANES AND ELECTRICAL SIGNALS, OTHERS INVOLVE THE RESISTANCE OR DENSITY OF THE AIR, AND SOME SIMPLY RELY ON CHANGING TEMPERATURES IN DIFFERENT FLUIDS.

• BUT THEY ALL MEASURE THE SAME THING, HOW MUCH WATER IS IN THE AIR, COMPARED TO HOW MUCH WATER IT CAN HOLD.

ATMOSPHERIC MOISTURE

• TAKE A MINUTE TO THINK OF A WAY THAT YOU MIGHT BE ABLE TO MEASURE THE AMOUNT OF WATER IN THE AIR…

• DISCUSS IT WITH YOUR TABLE AND THEN WRITE IT DOWN.