Howdy everyone and thank you for continuing on with module 8. In this video, we're going to explore water in our atmosphere. Like what is water vapor? Why should we care? And how do clouds form? One of the most amazing properties of water is that it has the ability to exist at all three phases at or near the Earth's surface. The solid form of water or ice is composed of molecules bound to one another by strong intermolecular attractions and this results in a highly ordered lattice pattern that gives ice its solid structure. Remember these lattice patterns are a property of minerals and ice is technically a mineral. Now heat energy can weaken those bonds and if enough heat is provided ice will lose its highly ordered pattern and it takes on a liquid form we know as water. Now this process is called melting and the heat involved in melting is called the latent heat of fusion. It takes approximately 336 jewels or 80 calories to change one g of water from solid ice to liquid. It then takes even more 2,260 Jewles or almost 600 calories to change the state of 1 g of water to a gas known as water vapor. Now this change is called evaporation or vaporization and the heat associated with that is known as the latent heat of vaporization. Now sometimes ice can change directly into water vapor and that process is called sublimation and that requires 2594 jewels per gram or about 680 calories and that just equals the latent heat of fusion and the latent heat of vaporization added together. Now as you know all of these processes are interchangeable. Water vapor can change back into water through condensation. Water can change into ice through freezing and even water vapor can change directly into ice and that's called deposition. In all of these reverse processes, the same amount of latent heat is given off. Now, water vapor is very important when we're talking about our atmosphere, and it's especially important when we begin our study of climate and weather. Now, there are many different ways we can measure water vapor or ways that water vapor is described in weather reports. You've probably heard the term humidity, dueoint temperature, specific humidity, and relative humidity and thought, well, what actually is the difference between all of these? Well, when we say humidity, we're talking about the amount of water vapor that is present in a column of air. How much water vapor exists at that point in our atmosphere. Now the Dupoint temperature is very important especially as we start talking about clouds. Now the Dupoint temperature is the temperature at which air becomes saturated. So the air can no longer hold any more water vapor. And when that happens we start to have condensation occurring. This means the water vapor um is starting to turn back into liquid water. That's because the air cannot hold any more water vapor. It's kicking it out turning it into liquid water. and that occurs at a specific temperature. We call our Dupoint temperature. Now, specific humidity is the ratio of the weight of water in the air to the combined weight of the water vapor plus that air itself. Whereas the relative humidity is the proportion of water vapor present in a parcel of air relative to the maximum amount of water vapor that could be present in the air at the same temperature. And this is what I have shown here. So, what do I mean by relative humidity? Well, depending on what temperature your air is at, there is a certain amount of water vapor can hold. So, the warmer the air is, the more water vapor can hold. And vice versa, the colder your air is, the less water vapor it can hold. So, relative humidity is talking about how much water vapor there is relative to the amount it can actually hold. So, the blue circle in each of these scenarios is the same size. So, we're talking about the same amount of water vapor. However, as you can see, the amount of relative humidity is different in each scenario, even though it's the same amount of water. That's because again, at different temperatures, we can hold different amounts of water. So, at 50° F, this amount of water has reached 100% relative humidity. It cannot hold any more water. This is the Dupoint temperature. So that means any more water vapor that is added is actually going to condense out into liquid water. We're going to have condensation occurring at this point. But if we heat that parcel of air up to 68° F, then we have a little bit more accommodation space. We can actually hold more water vapor here. So by changing it by 18° F here, you can see we went from 100% relative humidity to 52% relative humidity. So that means any water that is evaporated into the atmosphere here will actually be able to be held as water vapor because we have not reached our capacity. We're only 52% full of water. That makes sense. And if you heat that up even more to 86° F, we can hold even more water. That changes the relative humidity to 28%. So same amount of water in each scenario, but vastly different relative humidities. And that's because temperature is so important. Now, the hydraologic cycle describes how water is continuously circulated between the atmosphere, land surfaces, plants, the ocean, and even freshwater bodies. The largest amount of water transferred in any component of the water cycle are those involved in the direct evaporation from the ocean to the atmosphere and then in precipitation back over the ocean. Now precipitation includes any liquid water or ice that falls to the surface through the atmosphere. And the passage of water to the atmosphere through leaf pores is called transpiration. And the term evapo transpiration is the combined total water that is evaporated from the land surface and transpired from plants. If not all the precipitation at the land surface is evaporated then it is removed by the surface network of streams called runoff. Remember and in other places the water can info in infiltrate or soak into the ground and travels through groundwater before emerging back to stream flow and transfer from the land to the ocean again. Now, the water cycle operates as a closed system. So, nothing is added or lost. We're not adding water to our planet Earth, and we're not losing water from our planet Earth. We're talking about relatively the same amount of water. It's just constantly being cycled. It's a closed system. Now, clouds are the direct result of condensation in the atmosphere. And clouds are visible masses of suspended water droplets or ice crystals. And two conditions are necessary for the formation of clouds. One, the air must be saturated. And that's normally by cooling it down to the Dupoint temperature, which remember when we get to our Dupoint temperature, that's going to cause water vapor to condense because it cannot hold any more water vapor. And air most often cools to produce condensation when it is vertically lifted in the atmosphere and it experiences cooling by expansion. Another way air cools is by contact with colder air masses through mixing. Okay. Second condition for class to form. There must be substantial amount of small airborne particles called condensation nuclei around which liquid droplets can form. when the wa water vapor begins to condense. So we need something for the water to stick to more or less and clays are the most common nuclei but sea salt and even pollution provides nuclei for clouds to form. So remember clouds are the direct result of condensation in the atmosphere. They are visible masses of suspended water droplets or ice crystals and they need two conditions to form. The air has to be saturated and we have to have small airborne particles called condensation nuclei. There are three major cloud types stratus, cumulus and cirrus. Now stratus clouds have a layered appearance. They are also thin and normally cover a wide area. We classify these clouds based on altitude. When they're below 3 km in our atmosphere, they're simply called stratus clouds or nimbo stratus if they're precipitating. Between 3 and 6 km, they are called altoratus. Higher than 6 km, they're called seror stratus. Now, a second major cloud type is cumulus, which are thick, puffy, billowing masses that often develop to great heights. I call these my Toy Story clouds. These clouds are also subclassified by altitude. A stratouilis or just a cumulus, an alto cumulus and a cereumalis. Now very tall cumulus clouds extending from about 500 meters or 1600 feet at the base to over 12 kilometers or almost 8 miles at the top where they have their anvil-shaped heads are called cumulo nimbus. These clouds are often associated with violent weather including heavy rain, high winds, lightning, thunder, and even tornadoes. Now, a third type of cloud is cirrus clouds. They are thin and wispy streak-like clouds that consist of ice particles rather than water droplets. And I used to always remember them as looking like tales of horses. Now, they're only able to occur at altitudes higher than 6 km. and they're often marked by the prefix zero. Here are some examples of stratus clouds. Remember them as low clouds, layered, flat, cover wide areas. They're responsible for a lot of those gray days, and they're called nimbo stratus when they're precipitating. Now, again, these are responsible for those gray days that that we sometimes get in central Texas. We don't get them as much as we do in northern parts of our country. Um, but they're more common, I think, in the winter. But when you see strato as a prefix or suffix, know that it is referring to a flat layerike cloud. Now, cumulus are lowish clouds. Cumulus are puffy and fluffy. When you see a cumulus or cumulo as a prefix or suffix, know that we're talking about a puffy cloud like shown here. Again, Toy Story clouds. If you guys have ever watched Toy Story growing up, you'll know what I'm talking about. Then cirrus are high clouds, wispy, horsetailike. When you see as a prefix, know we're talking about a high altitude clouds because these only exist at high altitudes. So putting those prefixes and suffixes together, we can kind of interpret what we're talking about when we say stratouille. Strato means layered or flat. Cumulus means fluffy. So stratouilis is a lowaltitude cloud that is fluffy occurring in sheets like shown here. Alto stratus. Alto meaning midle. Stratus meaning layered or flat. Alto stratus means stratus clouds found at mid altitudes. Alto cumulus. Alto means midle again. Cumulus puffy and fluffy. So that means altoumulus are cumulus clouds found at mid altitudes. Cer stratus zero meaning high altitude stratus layered or flat. So zero stratus is stratus found at high altitudes. Hopefully you're getting the pattern here. Cerumulus zero meaning high altitude. Cumulus meaning puffy and fluffy. So sierra cumulus are cumulus found at high altitudes. And then my absolute favorite cumulone nimbus. Menacing looking multilevel clouds that extend high into the sky in towers or plumes and sometimes even look like a mushroom cloud. It is the only cloud that can produce hail, thunder, and lightning. It is dense, forming from water vapor carried by powerful upward air currents. And these are sometimes referred to as thunderheads. And we'll talk a lot about these when we get to inclement weather like severe thunderstorms and tornadoes. Now, condensation and cloud formation are critical for precipitation to occur. And that's probably intuitive because when it's raining or snowing outside, the skies aren't obviously clear. We have clouds. So, we need clouds in order to form precipitation. But not all clouds normally lead to precipitation. When water droplets within clouds first form, they are so small that the slightest upward air current keeps them airborne for long periods of time. So, they can never make it to the ground. Even if there were no air movement, the tiny water droplets would probably be evaporated as they travel through the unsaturated air below before they even hit the ground. Cloud droplets and tiny ice crystals must grow by a factor of 1 million if they are to fall fast enough to survive the descent to the surface. And here are the many different forms of precipitation that we have that we will revisit again when we get to inclement weather. But as you can see, just to introduce it, we have rain. This is, and again, a lot of this precipitation actually starts off as frozen higher up in the atmosphere. But rain obviously reaches warm air fairly quickly as it falls down. Freezing rain enters a warm air column, but right before it hits the ground, it enters cold air again. So, it freezes when it reaches the cold surface on contact. Sleet, same thing except for you're reaching cold air sooner in its descent. So, it freezes before it hits the ground and it hits the ground as little ice pellets. And then snow remains frozen the entire descent. Again, we're going to revisit all these precipitation types when we get to our inclement weather. And that's because precipitation causes a lot of hazards. Heavy rain or long duration rain leads to flooding. And we talked about flooding already this semester. Freezing rain is probably the most hazardous when we're talking about driving conditions because they can bring down trees and utility poles like shown here in these pictures. Sleet also leads to hazardous driving conditions. And then we have blizzards which are hazardous and they provide lots of hazardous driving conditions. They can cause hypothermia, frostbite. Carbon monoxide poisoning is very common in blizzards and they also can bring down trees and utility poles. And we'll spend more time talking about different kinds of precipitation hazards when we get to inclement weather. But that's all we're going to talk about in terms of water vapor and water in our atmosphere. I'll see you in our next video.