Kelvin Helmholtz Clouds in the Jerusalem Skies

Blog topic: 
Yesterday, while talking to my wife, I noticed that Kelvin-Helmholtz Clouds were forming in the sky behind her. These are cirrus clouds that due to the Kelvin-Helmholtz instability grow vortex billows. They arise from very large shears in the velocity fields, which is this example arise just below the jet stream.

The phenomenon is very similar to the excitation of sea waves by the wind, or waves on the surface of the small water flow coming out of a faucet (the later formation of drops is due to surface tension, an altogether different phenomenon).

Here is a picture I took, while a time lapse movie I made can be found here. Due to the lack of any prior notice, I used a very low tech method to capture the movie's frames... a still camera, a stop watch and my finger. This is also the reason for the slight jitter in the movie. (The time lapse movie is 360 times faster than real time).
Kelvin Helmholtz Clouds forming south of Jerusalem. The clouds top is at about 8 kms above sea level (the hilltops are about 0.8 km above sea level. The photograph was taken from Mevasseret Zion (a suburb 10 kms WNW of Jerusalem. The villages of Ora and Aminadav are on the top of the background ridge. Halfway up the ridge is the Ein Karem Medical campus of the Hebrew University and Hadassah Hospital. The valley between the foreground and background ridges is that of Soreq, while the foregroud is of course Mevasseret Zion).


Comments (5)

  • anon

    Hi Nir!

    Congratulations for your superb work! It is refreshing to read about the dark side of the moon, that is, about these alternative theories of yours regarding the actual causes of global warming. Although I am not an astrophysicist, climatologist, geophysicist and what not – I am only a medical scientist who spends all of his time trying to understand the physical, structural, functional and physiological properties a certain membrane proteins – I have never quite understood how the IPCC group had managed (over the years) to come up with such hard evidence that global warming was anthropogenic and I have always been (and am still concerned) about this climate sensitivity issue (among other things).

    In fact, my main concern at this stage is that empirical simulation models are being used to draw very strong and potentially very influential conclusions while most, if not all of these models have probably never been truly validated for obvious reasons. I am always wondering whether climate scientists do know if the variables they use in these models are weighted correctly against each another and whether they are not missing a whole bunch of other variables (besides the clouds…) that could have a drastic impact on climate changes. Am I mistaking? I have the impression that many postulates have been made just before or even after the hockey stick era and this, on the basis of oversimplistic assumptions and that many scientists are trying to impose their views despite the uncertainties of climate predictions.

    Be that as it may, I am wondering if you could answer three questions of mine (perhaps simple to you) that have been puzzling me for quite some times. Any input would be greatly appreciated.

    First question: Are there any evidence that the terrestrial nucleus could actually be changing over time and account for some of the differences that have been observed in mean surface temperatures throughout various centuries? Would the impact of the “nucleus variable” be null (given that sun and cosmic rays appear to exert differential effects on climate changes) or do we really know?

    Second question: Is it appropriate to model climate changes based on mean “pan-terrestrial” variables? Has anyone really validated this method of quantifying “warming” in the past? In other words, do models describing mean temperature changes make a good job at describing local temperature changes all around the world and are we sure that the weights of individual variables are the same across the planetary surface? What if the variables that drive climate in the North Pole (NP) differ markedly from those that drive climate in the equator? How can we then really address the issue of anthropogenic warming in a concise way? If region A (the NP), considered by many to be at the center of future catastrophes, has warmed up drastically mainly because of variable “x”, and if region B (Southern Canada for instance) has warmed up mainly because of variable “y”, should the mean temperatures of A+B be explained by the mean effect of x+y? So if this is the whole idea behind global warming, are we not assuming quite simplistically that these means can be correlated against one another simply because x and y = CO2 to a large extent? Do we know this for a fact?

    Third question: What is actually going on in the North Pole? This puzzles me a lot and I am not sure that the climate circulation models (based on mean temperatures across the globe) really help us understand why this region has become so warm in the last decade or so, and why other regions have probably “resisted” to such drastic variations or have even become cooler. Given that the mean (global) temperature of the earth has increased by less than 1 degree but that of the North Pole by less by more than 1 degree, other regions must have cooled off a little, no? What do you think Nir? What is going on in the North Pole?

    Thanks again for all of your interesting thoughts on the subject of global warming. I had posted a message a few days ago but might have had screwed up somewhere around the “posting” step. I hope that you will publish my message and provide me with some answers. I think that your relatively recent incursion in the field of CO2-driven climate changes is going to make a lot of good to this world even if many IPCC members appear to think otherwise. Keep up the good work!



    Feb 27, 2007
  • anon

    I'm not sure I understood your questions properly, especially not the first one, though I think I can shed some light for you on the north pole.

    The reason that the pole appears to warm (or cool, depending on the period) more than say the equatorial region has to to do with the way that the polar regions are warmed. In the equator, the temperature is reached primarily through the equilibrium between radiation being absorbed and radiation being emitted. In higher latitudes however, this is not the whole story, because energy is advected polewards from equatorial regions using latent heat of water vapor (water evaporates at low latitudes, takes heat, and when it condenses at high latitudes, it releases that heat again back to the system). For this reason, the polar regions don't just depend on Earth's radiative equilibrium but also on the internal energy advection efficiency.

    The next interesting point to note is that as Earth warms, there is much more water vapor in the atmosphere, this implies that a warm Earth and more efficiently warm the poles, and the equatorial-polar temperature different decreases. For this reason, climate variations are much more pronounced in the poles.

    With respect to the area, the equatorial regions are way more important than the poles. For this reason, the polewards fluxes are not very important for the equatorial regions.

    -- Nir

    Apr 07, 2007
  • anon
    Organic Chemistry (not verified)

    I have never seen clouds like that before. Very interesting. My only question: is the Kelvin that the phenomenon is named after the same Kelvin as the Kelvin temp scale/absolute zero?

    Apr 06, 2007
  • anon

    Same Kelvin. A century ago, science was less specialized than today so people generally contributed in more fields than is possible today.
    -- Nir

    Apr 07, 2007
  • anon

    I saw some very much like that in the sky over northern Kentucky once, but didn't have a camera. Thanks.

    Nov 04, 2009