Physics 137 - Introduction to the Atmosphere and Weather                                                                                Homework Key - Assignment #16
Revised 02 November, 2009

16-QT2.  When glaciation was at a maximum (about 18,000 years ago) was global precipitation greater or less than at present?  Explain your reasoning.

    Probably less, because of lower temperatures and consequent lower atmospheric water content.

16-QT4. Explain why periods of glacial advance in the higher latitudes tend to occur with warmer winters and cooler summers.

    Warmer winters would tend to produce increased high latitude snowfall because of the higher atmospheric water content. Cooler summers would retard the melting of that greater snowfall, causing an increased rate of snow accumulation and glaciation.

16-QT5. Explain two different ways that an increase in sulfate particles might lower surface air temperatures.

    Sulfate aerosols tends to promote surface cooling by (1) reducing the solar radiation reaching the surface by scattering incident solar radiation directly back into space, and (2) by serving as condensation nuclei for cloud formation, thereby resulting in clouds with more but smaller water droplets which would therefore be more reflective of solar radiation. This would also reduce the amount of radiation reaching the surface.

16-QT6. Are ice ages in the Northern Hemisphere more likely when:  (a) The tilt of the earth is at a maximum or a minimum?  (b) the sun is closest to the earth during summer in the Northern Hemisphere, or during winter?  Explain your reasoning for both (a) and (b).

    (a)  Ice ages are more likely when the tilt is at a minimum. A tilt minimum tends to moderate seasonal effects with consequent warmer winters and cooler summers. For reasons given in QT2 above this would tend to trigger glacial advance at higher latitudes, which glaciation would then encroach on lower latitudes.

    (b) For the same reason, a moderating of seasonal effects with a resultant increase in glaciation, ice ages are more likely when the earth is closest to the sun during winter.

16-QT8.  The oceans are a major sink (absorber) of CO₂.  One hypothesis states that as warming increases, less of CO₂ will be dissolved in the oceans.  Would
    you expect the earth to warm or to cool further?  Why?

    If warming reduces the amount of CO₂ dissolved in the oceans, that will release more CO₂ to enter the atmosphere.  Such a change would enhance the greenhouse effect, causing even further warming.  Thus the associated feedback will be positive.

16-PE1. If the annual precipitation near Hudson Bay (latitude 55°N) is 38 cm (15 in.) per year, calculate how long it would take snow falling this region to reach a thickness of 3000 m (about 10,000 ft). (Assume that all the precipitation falls as snow, that there is no melting during the summer, and that the annual precipitation remains constant. To account for compaction of the snow, use a water equivalent of 5 to 1.)

Time =	(3000 m snow)	= 1580 yrs.
	(0.38 m water/yr)(5 m snow/m water)