Class 16 - Earth, Venus, Mars - Dynamics 2

Reading:

Atmospheres - Goody & Walker Chapter 4
New Solar System - Ch 13.

Venus - SO2 Cycle
Mars - CO2 Cycle

Venus - SO2 Cycle

Venus in UV, Visible and IR

The dark in UV is due to some unknown absorber (ask Larry Esposito next week what he thinks it is). Visible is just cloudy. The near IR sees through the top layers of the clouds to the lower clouds.

So, what's with the sulfuric acid clouds? Here's the SO2 cycle for Venus - the simple version

and now the more complicated version (constructed by Bruce Fegley)

Note:

Photochemistry above, thermochemistry below (high density, remember)
two cycles - a reduction cycle and an oxidation cycle - coinciding.
Some think LIFE could have developed in these clouds.... next thursday's guest lecture by Larry Esposito
Remember - low down in the high density troposphere winds are thought to be very gentle. High above there are broad, racing streams circling the planet in 4 days (60 times rotation rate).

Weather forecast for Venus?

Mars - CO2 ice ("Frost") Cycle

With Mars the presence of water is less important for affecting heat sources/losses/transportation - it's CO2 and DUST.

And seasons.... But first let's look at the Mars Global Circulation Model - MGCM

Fig 4-17 - early theoretical models circa 1972

?? make sense??

Here's a 2003 diagram that might help

A 2-cell Hadley system....similar to Venus.... with a small cell at high latitudes? Note 2 westerly jet streams

But there is a strong seasonal asymmetry - we need to look at seasons on Mars.

Seasons on Mars

Mars' orbit: semi-major axis a=1.52 AU, eccentricity e=0.0934, obliquity=25.19 degrees. Albedo = 0.15

Puzzler 1: What is the subsolar heat flux (W m²) at (a) aphelion~N.summer and (b) perihelion~S. summer?

Puzzler 2: What is the temperature at the subsolar point at (a) aphelion~N.summer and (b) perihelion~S. summer?

Top plot shows solar heating, bottom shows pressure - vs. time of year

Now compare the circulation pattern at Northern winter / Southern summer solstice

single, trans-equatorial Hadley cell, smaller cell at winter pole. One E jet, one W jet.

Seasonal Polar Caps

Mike Caplinger Site - about season, shows S polar cap receeding

Sizes of the N (left) and S (right) polar caps - RED = residual polar caps. BLUE - elevated regions of layered/eroded material

Laser altimetry of the N polar cap

Changes in the N polar cap over a couple of years.

High resolution view of the layered structures left when the polar cap sublimes.

and the S pole - reflectivity - indication of snow cover

How much of the polar caps are CO2 vs. H2O? Good question. 2003 papers suggest ~half.

Why do polar caps never get colder than 150K? That's the freezing temperature of CO2. What is released when CO2 freezes?

How deep is the winter snow on Mars? Movie - Not much - about a meter (all that fuss for 1 measily meter of snow???) - the total mass is a few percent of mass of Mars. Note N vs. S.

And the seasonal change in mass....

Water vapor distribution vs. time/season - units = "precipitable microns" - that is microns of water (covering a unit area). Lowest humidity on Earth, anyone?

[Note that if we take the average amount of water vapor on Earth to be 1/100th that of air - then the surface density of water vapor is ro = 1.2/100 kg m^-3and the column mass of water vapor is Mc= ro H = 0.012 x 8000 kg m^-2~ 100 kg m^-2. If all this water then condenses, how thick a layer of water would this make? Well, the density of water is 1000 kg m^-3 -the total column mass is the same - so the depth of liquid would would be 100 kg m^-2/ 1000 kg m^-3 = 0.1 m=10 cm. Not that thick - but a heck of a lot more than the microns of water on Mars!]

Fig 6 - Seasonal variation in water ice cloud abundance from the MGCM

Now add DUST....

The dust storms can have a huge effect on the temperature profiles

Summary of Mars' atmospheric circulation....