I think it's fair to say that the Arctic is really not a place for sun lovers. Well, of course it's dark for half the year in the Arctic. In fact, if we are at the North Pole as we remember, the sun is below the horizon for six months of the year. Now of course, in the summer we can have the 24 hours sun right. That's the Midnight Sun, so you might think that's great for sun lovers. But the point is, is that the Arctic is a very, very cloudy place, and so even though the sun maybe above the horizon for 24 hours a day. For long periods of time the sun just is not shining, and it's because of the clouds, of course. So the Arctic really is, for the most part, pretty cloudy place. Certainly there's exceptions. The top of the Greenland ice cap for ice sheet, for example, is doesn't have as much cloud cover as other areas. But really, the Arctic is a pretty cloudy place, especially on the Atlantic side of the Arctic. The Atlantic side of the Arctic it is particularly cloudy. Now there's many different cloud types in the Arctic of many of the cloud types that we find in the Arctic are just the sort of things that we would see in middle or lower latitude. Cirrus clouds, cumulus clouds, altocumulus and the like. But it's also very, very important to recognize is that clouds in the Arctic have tremendous impacts on the surface energy exchanges. How much solar energy gets down to the surface is very, very dependent on cloud. Clouds are also important because they emit long wave radiation that is radiation in longer wavelength down to the surface. So clouds can be very, very, very important. There's also some evidence, although it's still a bit controversial. That Arctic cloud cover may in fact be increasing. Well, what does the Arctic look like from space? Well if you look down at the Arctic from space from a satellite image and that's what I'm kind of showing here. Which is a mosaic of a number of satellite passes from something called a moderate resolution imaging spectral radiometer aboard a NASA satellite. This is in summer and it's just looking down at the Arctic basically from the pole. Now you can see a Greenland down kind of at the bottom left. It's very white because it's an ice sheet, but also not a lot of clouds there. But if you look elsewhere yet is sea ice there. But it's a very, very, very cloudy place too. So the Arctic looked quite from outer space because you've got sea ice. You've got snow, but also a lot of clouds and clouds of course, are white. Well, let's get back for a minute and 1st asked the question. What are clouds actually made of? Well, the answer is that clouds could be made of either liquid water droplet or ice crystals, or actually a combination of both. In other words, they could be made of one or either or both. They're not really made of pleasant dreams, although I suppose in a more metaphorical sense they might be. But some people think all clouds is water vapor, no clouds are actually liquid droplets or ice crystals. Now those droplets get big enough precipitation could fall if the ice crystals get big enough, then snow could occur as well. But the clouds themselves are made of either liquid droplets or ice crystals, or actually a combination of both. And these mixed face clouds that are liquid water and ice crystals are quite common in the Arctic. Makes sense because we have a lot of snow. Let's think about the extent and types of clouds that we see in the Arctic. Well in terms of the extent Over the central Arctic Ocean. What we tend to have is generally 60 to 80% cloud cover. That's a lot of clouds. And, a lot on the Atlantic sector. I mentioned this particularly cloudy. It's more than 80% really just year round. It's just a pretty darn cloudy place. What do we see in summer? We see a lot of Arctic Stratus. This is just list low level stratus. When you see these sheet clouds that cover most of the Sky and there are fairly low level in the atmosphere, maybe they've secured the mountains and things like that. That'll tend to be what we call stratus cloud the sheet clouds we see a lot of that in the Arctic to get even as a special name Arctic Stratus. But the Arctic, as I noted, is also home to many different cloud types. Many of them that we're familiar with down in the middle latitudes, including even cumulonimbus clouds. Cumulonimbus clouds are those clouds that we associate with thunderstorms that have that big an Volt off at the very top that really made of ice crystals. So the Arctic, as you know, as I say, clouds that we're familiar with. In terms of the amounts of cloud, this is the seasonal pattern of cloud cover over the central Arctic Ocean. What I'm showing from left to right in the X axis is month and the middle that basically June middle of the year and on the Y axis what I'm showing is the percent of cloud cover. That is basically if you would look up in the sky and say what percentage of the cloud is what percentage of the sky is covered by clouds. This is what you'd see, so these are actually from surface observations. Well, it turns out in the central Arctic Ocean. If you look at just that dark line, the Black line solid line. You range from about 60% cloud cover in the winter to about 80% in the summer, so somewhat less in the winter than in the summer. Makes a little bit of sense because of course in the winter is colder, not as much water vapor in the atmosphere. So it's actually harder to get clouds to form. That dotted line below it, just shows the amount of low cloud cover. What I mean by that is this cloud cover that is near the surface, which is generally this Arctic stratus that I mentioned. So yeah, 60% in winter 80% in summer. Now of course in the winter if you're a sun lover, doesn't matter. because the sun is probably going to be below the horizon, but in the summer it's just a cloudy place. Here's the Atlantic side of the Arctic. Same kind of image, but I'm showing the Atlantic side of the Arctic. Basically 80% cloud cover across the year. There's very little seasonal cycle and most of that is as low cloud cover this Arctic Stratus. So yeah, it's a pretty darn cloudy place. This is a photograph I took some time ago around Serreze bar. And it just shows some of that Arctic stratus that just kind of grey ,low Arctic stratus is looking back up from the ocean there. Out to some glaciers and ice caps, but that is pretty much like a lot of the Arctic is going to look like in summer. Just a lot of clouds. This figure here also I forget who took that of me, but it was some years ago in Ken on the North slope of Alaska. But it was showing some of the clouds that we're familiar with. There's some cirrus clouds there. Cirrus clouds are these clouds that are high in the atmosphere, they're called mayors tales. These wispy clouds that you often see coming across the Sky. Those are made of ice crystals. Those are ice crystal clouds. Below that we see clouds at a lower level. These are cumulus clouds. Cumulus clouds like we see in middle latitudes, these puffy clouds they can look like castles in the sky and things like that. They can eventually grow into cumulonimbus, which is we associate with thunderstorm. But we don't have too many thunderstorms up there, although they do actually occur once in awhile. Here's one, this was a crazy one. This was a photograph I believe I took this one back in 1982. When I was doing work on northern Ellesmere Island, 82 degrees north. And this actually was a cumulonimbus cloud in the very, very high Arctic not a lot of vertical development like we would see in the lower latitude. But yeah, we had some electrical discharge from it scrambled some of our electrical equipment. Never seen anything like it may never see anything like it again, but it was pretty remarkable. The background you can kind of see one of our tents and looks like the clouds right over there tent. I think it actually was at that point. A question, how do clouds actually form? Well, the answer is not that they just do what we don't know why. Well, we certainly know how clouds form. Well, it goes back to the cooling and condensation of rising parcels of air. We have parcels of air such as a kilogram of air, say, and if it rises through some mechanism, a warm front, cold front. Convective processes like we'd associate with thunderstorm, it's going to cool and it could cool to its dewpoint. That's where the relative humidity is 100%. And condensation would occur and the water vapor would transform into liquid water droplets or ice crystals. Because clouds could be really one or the other, or both, so it's cooling and condensation of rising air. It's not cooling and condensation of descending air because air descends, it actually warms up, and that's not what we want. We want the air to be rising and cooling so that condensation can occur, and it's not that solar radiation excites water vapor. No, that's not it either. Cooling and condensation of rising air til we get to 100% relative humidity or we called the dew point and then clouds will form. Another interesting thing about Arctic clouds is the pronounce. Cloud radiative effects has been a great deal of work on this. The thing is, clouds have two effects on the surface energy receipts that we get at the surface from longwave radiation and solar radiation. Clouds reflect solar radiation back into space. Clouds are white. They have a high albedo. They reflect solar radiation back into space. But clouds also emit longwave radiation back to the surface. They're very very affective in doing so. There's always longwave radiation emitted from the atmosphere back to the surface because there are greenhouse gases in the atmosphere. But cloud cover tends to accentuate that effect. In other words, under clouds, we have more longwave radiation reaching the surface than when it's clear. Well, so there's two kind of competing effects here. The reflectivity of the cloud and the effect of clouds on promoting more longwave radiation to the surface. And the thing in the Arctic is, except for summer, the latter tends to win, the longwave effects of cloud for most of the early Arctic are warming agent, kind of counter to what we experience in the middle latitudes. This little cartoon here's I'm trying to show list the situation with no cloud. There is shortwave what we call solar radiation reaching the surface, that shown in the blue arrow. There's also longwave radiation being received at the service and that's because there are greenhouse gases in the atmosphere. But now let's introduce cloud. What happens if we introduce a cloud layer? Well, shortwave radiation, again in the blue, it comes down, but some of this just reflected away fraud by cloud so we don't have as much coming to the surface as we would if it was clear. But as I mentioned, the clouds actually lead to a greater emission of longwave radiation to the surface. They accentuate, or let's say they work in tandem with the effects of the greenhouse gases in the atmosphere. So we have more longwave radiation received at the surface when we have cloud then when we don't. So as it turns out, don't you have clouds? There's more total energy coming down to the surface from radiation shortwave and longwave than with no clouds. So for most of the Arctic and most of the year, clouds actually warm the surface. This is another very, very important effect of clouds. Evidence, for changing cloud cover, is Arctic cloud cover changing? There is some evidence that it is. Well, especially in autumn, were CIs has been lost because if we have now areas of open water where we didn't have it before, now we have a moisture source. We can put water vapor in the atmosphere, more likely to get cloud formation, probably more likely to get more precipitation as well. And this also may be contributing to Arctic warming. because as I noted, with more clouds, clouds tend to warm the surface. So as we move into a new environment through the 21st century with less sea ice, could we be seeing more cloud cover, especially in autumn, contributing to the strong Arctic warming that we've already seen? So this is really a big research question out there. And just illustrates, again, the importance of cloud cover and the fascinating processes that occur in the Arctic. Thank you.
