Comments on: Flight 447 and the ITCZ https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/ Sat, 14 May 2011 03:19:01 +0000 hourly 1 https://wordpress.org/?v=6.4.8 By: Greg Laden https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502957 Sat, 14 May 2011 03:19:01 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502957 “Can’t remember where I heard all of this, but I always tell my students about it in my intro met class. ”

There should be a wiki of just stuff we all tell our students in intro classes even though we don’t really remember how we know them.

]]> By: Doug https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502956 Fri, 13 May 2011 22:59:06 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502956 Actually the axial tilt is about 23.5 degrees relative to a plane normal to the ecliptic. It’s 66.5 degrees off the ecliptic itself. The variation in tilt is why the north star is not always the north star. I once heard a theory that the Arthurian legend was rooted in the movement of the axis. At one time, celestial north was in the constellation Draco, the dragon, but it has shifted to polarism which is in Ursa minor (the small bear). Arthur means “the bear”, and Arthur’s father was Pendragon, which means “head of the dragon.” Can’t remember where I heard all of this, but I always tell my students about it in my intro met class.

]]> By: Greg Laden https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502955 Fri, 13 May 2011 20:30:45 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502955 More on the tilt and relationship to climate change here:

http://scienceblogs.com/gregladen/2009/01/global_warming_the_blog_epic_0_6.php

Also, this docuentary is pretty darn good: Nova: Crash of Flight 447

]]> By: Greg Laden https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502954 Fri, 13 May 2011 20:21:59 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502954 Eunoia,

Actually, that isn’t correct either. The tilt of the axis varies over time and is almost never exactly 23 degrees. That’s why we have ice ages!!!

Ah, a little pedant to pedant battle does one good…

But seriously, yes, you are almost exactly correct. Indeed, there is a thing called the “Climatological” or “Climatic” equator, which reflects the offset of the equator against the sun’s plane and tracks the seasonality.

]]> By: Eunoia https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502953 Fri, 13 May 2011 20:06:33 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502953 You wrote “The earth is a big ball, and spins on an axis that is perpendicular to the plane of the sun.”

Er, no, that’s wrong. The axis of spin is 23° off the plane of the ecliptic. That’s why we have seasons 🙂

]]> By: MadScientist https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502952 Fri, 13 May 2011 15:55:11 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502952 @gwen: It’s not always rough everywhere when crossing the equator (and the ITCZ can drift a few degrees N and S as well). However, when it *is* rough, as Greg pointed out, commercial aircraft can’t dodge it. Near the equator the turbulence can extend to over 16km altitude as opposed to jet aircraft ceiling (max) altitudes of 12-14km depending on the aircraft type, nor do aircraft typically cruise at their max. altitude. Another hazard to aircraft are ‘gravity waves’ which occur in the vicinity of mountains (the Rockies are notorious) and I’d rather have a nice ride in the ITCZ. I flew through gravity waves around New Zealand once and it was the roughest ride I’d ever had in a heavy aircraft. As in teh case of the ITCZ, flying over/near a mountain won’t necessarily give you a rough ride.

]]> By: gwen https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502951 Fri, 13 May 2011 05:54:56 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502951 Wow, I’d never even heard of the ITCZ!! I have flown near the equator (in a prop plane, pre-jet flight), but never across the equator. I’ll keep that in mind next time I decide on a travel destination.

]]> By: daedalus2u https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502950 Fri, 13 May 2011 04:28:15 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502950 When I make my multi-million km2 floating plantations to make biofuels from plants growing in sea water, I will start by putting them at the equator to avoid hurricanes.

Once they get big enough to reach far enough from the equator to be hit by hurricanes, I will be able to control the weather sufficiently that they will not be hit.

]]> By: Doug https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502949 Fri, 13 May 2011 04:06:56 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502949 I’ve always considered the ITCZ to be misnamed. It should be the Intertropical Nonconvergence Zone, because the trade winds generated by the Hadley circulation don’t mix. The “gap” in between them can be a place of eery calm. I’ve read accounts of sailors (and I mean real sailors, on sailing vessels) get becalmed there for weeks at a time due to migration of the thermal equator. Sometimes, they starved or went mad.

]]> By: daedalus2u https://gregladen.com/blog/2011/05/12/flight-447-and-the-itcz/#comment-502948 Fri, 13 May 2011 01:17:31 +0000 http://scienceblogs.com/gregladen/2011/05/12/flight-447-and-the-itcz/#comment-502948 The reason that rising air always causes thunderstorms is because of adiabatic expansion. As air expands, the volume increases and it takes energy for the volume elements to push against atmospheric pressure and generate work while it is expanding. That is why expanding gases always cool.

The vapor pressure of water is exponential with temperature, so as the air cools, the vapor pressure of water goes down and the water condenses, liberating its heat of vaporization.

If the temperature gets below the freezing point, the water freezes and you get hail. That might be what happened with flight 447, there was hail, a piece of hail hit one of the pitot tubes used to measure air pressure and wind speed and they lost that data. Water can also get supercooled, so it is liquid but at -20. Then when it hits surfaces it can freeze. That can block pitot tubes too, and can accumulate on wings and reduce lift.

The reason that it usually becomes clear at night is because the air near the ground cools, the air above it falls, by falling the air is compressed, it heats via adiabatic compression and the little drops of water that comprise clouds evaporate.

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