lecture 3: Water in the atmosphere 4

Question 1

RELATIVE HUMIDITY: DIURNAL & MERIDIONAL VARIABILITY

Answer 1

• Relative humidity varies throughout the day, mostly because of the diurnal temperature variation (with rather unchanged amounts of water vapour in the air at the same time).
• The meridional (= across latitudes) variation of relative humidity shows high values in the moist-warm tropical regions and in the cold high-latitude regions. Low RH values can be found at 30o N and S at the location of large deserts.
( compare this with the meridional distribution of specific humidities!)

Question 2

RELATIVE HUMIDITY IN THE HOME

Answer 2

• Cold winter air contains very little water vapour.

* Warming of the air through central heating will reduce the relative humidity to as low as a few percent.

Question 3

RELATIVE HUMIDITY IN THE HOME- effects

Answer 3

As a consequence following adverse effects may happen:
• Evapotranspiration from indoor plants will be very high (more watering required)
• Irritations of the human skin due to moisture evaporation (cracking, dryness, itching)
• Mucousmembranesinthehuman respiratory system suffer from dryness: incubation of bacteria is easier possible resulting in infections of the respiratory system.

Question 4

Dew and frost

Answer 4

• During clear & calm nights the earth’s surface cools rapidly due to radiative cooling.
• Air that comes in contact with cold surfaces cools by conduction.
• As leaves, twigs and blades of grass cool below the dew point temperature
water begins to condense upon them, called dew.
• If the air cools below freezing point the dew will freeze, resulting in frozen
dew.
• When the dew point is below 0 oC then the water vapour can deposit directly as frost (ice crystals).