Navagear » Climate and Weather

Why does smoke cause a reddish sun? And why is the sky blue?

Tim — Thu, 05 Aug 2010 12:57:00 +0000

Until today, I didn’t actually know why the sky is blue, and now I do. You may think you know why the sky is blue, but perhaps you’ve been misled all these years? I was!

Pacific Northwest weather guru Cliff Mass has the story at his blog:

On Sunday a number of you noted the reddish color of the sky and the orange-red hue of the sun. I mentioned in my blog that day that this was the result of smoke from wildfires, blowing in from BC (the main origin) and eastern Washington.

But why does smoke cause the red coloration?

The reason? The scattering of light by small particles in the atmosphere–also known as Rayleigh Scattering. It also explains why the sky is blue!

The light from the sun contains all wavelengths and is essentially white. White light possesses contributions from all wavelengths (or colors) in the visible spectrum (see figure). On the shorter wavelength side there is blue and on the longer wavelength side there is red.

It turns out the small particles in the air (small compared to the wavelength of light) can scatter incoming light into various directions and that they scatter short wavelengths (purple and blue) much more than longer wavelengths (orange and red).

So the light coming in from the sun is white with all wavelengths, but the molecules in the atmosphere scatter blue light more than other wavelengths.

Weather alert for boaters from Cliff Mass

Tim — Sat, 31 Jul 2010 16:06:16 +0000

Cliff Mass’s wonderful weather blog has this item today, which discusses the weekend’s weather patterns, but also mentions a project that regional mariners ought to be aware of:

Please help researchers evaluate how to communicate weather forecast information. The survey will take you only 20 minutes to complete. Survey data will be used to improve weather forecast products designed for boaters. If you own a boat and would like to participate, please click on the link below. Thank you.

Click to take the survey

Davis Vantage Vue weather station

Tim — Tue, 02 Feb 2010 23:02:07 +0000

I’ve got a sort of terrible weather station at home. Not much more than a pair of temperature sensors and humidity and barometric pressure sensors.

It’s much better than nothing, but sometimes I wish I really had the whole kit –n- kaboodle.

Behold the Davis Wireless Vantage Vue weather station…

Very cool, and you can see one at North Pacific Marketing (C2113, upstairs). Or check out the website at vantagevue.com.

Weems & Plath Electronic Barometer

Tim — Mon, 14 Dec 2009 21:40:00 +0000

My friend Dan Richman has an excellent review of the Weems & Plath 4002 electronic barometer over at Three Sheets Northwest. Here’s an excerpt:

Watching the change in barometric pressure is a time-honored way to predict the weather.

Yet barometers don’t make that easy to do. Barographs, which chart those changes, are obviously far more useful. But traditionally they have been large, delicate mechanical devices unsuitable for anything except ships.

The Weems & Plath Electronic Barometer 4002 is a digital barometer with an LCD current-pressure display and a separate LCD barograph display. Retailing for $170 to $205, it’s an excellent weather instrument, ideal for home use and for consultation before a day sail. Yet it has numerous design shortcomings, and I’m not sure it’s weatherproof enough to be used on board. I do not recommend it as a timepiece, moon phase indicator, yacht-race timer or anything else it purports to be.