Parhelic Circles, Ice Haloes and Sun dogs over Jerusalem

A few weeks ago, a few students saw a nice phenomenon in the sky. Knowing I liked this kind of stuff (and that I may be able to explain it), they called me out of the office to look at the sky. Above us was a nice and almost complete parhelic circle. Unlike the usual 22° halo, often seen around the moon and occasionally around the sun, the parhelic circle keeps a fixed angle from the horizon, not from the bright object.

On the IPCC's summary for policy makers, and on getting interviewed without noticing

Yesterday I was surprised to find out that the IPCC didn't really come out with the Fourth Assessment Report (4AR). I was also surprised to find an article with something which appeared to look like an interview of me. Since I am not senile (getting there, but not just yet) I found it strange that I didn't remember actually being interviewed!

Climate Sensitivity - an interesting IPCC bias

Some time ago, I noticed an interesting bias in the TAR scientific report (the third assessment report of the IPCC - the intergovernmental panel for climate change) regarding the climate sensitivity, that is by how much the average global temperature will increase if we double the amount of CO2. The report mentions quite a few times that climate sensitivity "is likely to be in the range of 1.5 to 4.5°C". Why is this interesting? Because ...

On Climate Sensitivity and why it is probably small

What is climate sensitivity?

The equilibrium climate sensitivity refers to the equilibrium change in average global surface air temperature following a unit change in the radiative forcing. This sensitivity (often denoted as λ) therefore has units of °C/(W/m2).

Often, instead &\lambda;, the sensitivity is expressed through the temperature change &Delta Tx2, in response to a doubled atmospheric CO2 content, which is equivalent to a radiative forcing of 3.8 W/m2. Thus, &Delta Tx2 = 3.8 W/m2 λ

"SKY" experiment demonstrates link between cosmic rays and condensation nuclei!

After a long embargo, results from the Danish National Space Center (DNSC) Sky experiment were finally published in the Proceedings of the Royal Society. The results demonstrate a clear link between cosmic ray induced atmospheric ionization and the formation of condensation nuclei, thus strengthening the claims that cosmic rays affect cloud cover and climate (and consequently implying that a large fraction of 20th century global warming should be attributed to the increased solar activity).

Comments on nature's "A cosmic connection"

Last week, a report by Jeff Kanipe appeared in nature. In it, Kanipe explains the solar → cosmic-ray → climate connection, and the planned CLOUD experiment in CERN, expected to finally resolve the issue. Given that my work is mentioned in the review, I through I should mention a few relevant points.

The coming of another ice-age?

Blog topic: 
A few days ago I stumbled upon an interesting article from Time magazine, entitled: "Another Ice Age?". No it is not a recent article. It is politically incorrect to talk about global cooling these days. The article appeared in 1974, after "three decades of cooling" prompted some to believe that an imminent ice-age may be coming. It is interesting to read it in perspective, and perhaps there is a lesson we could learn from it. Here are a few excerpts from it. Read and enjoy.

Exhale Condensation Calculator

If the temperature is low enough or the humidity high, you can observe condensation (i.e., "fog") forming in your exhaled breath. This calculator estimates whether your exhaled breath will condense, and if so, the range of mixing ratios for which the "fog" will form and the maximum condensed water content (the higher it is, the "thicker" the condensation).

If you're interested, there is a much more detailed explanations of the condensation process.

Exhaled Condensation Calculator
Using the above equations, we can calculate whether the exhaled air will condense. Enter the conditions of the outside air (and modify the exhaled air parameters if you wish), to see whether your breath will condense, or not.

Snow at above freezing temperatures

Did you ever wonder how can it snow at above freezing temperatures? Well, the naive explanation is that it simple takes time for the snowflakes to melt once they penertrate above freezing air, as they descent downwards to the ground. As it turns out, this is the reaons why hail can fall in warm weather. The hail stones simple fall fast, too fast to let the warm air melt the hail.

With snow flakes, this isn't the case. The flakes fall very slowly and the large surface to volume ratio ensure that the flakes can reach thermal equilibrium with the environment on time scales much shorter than their descend time. So, how can the flakes remain frozen as they fall?