So I wanted to start off this thread with a little bit of knowledge on the basics and when I mean basics we have to start at the bottom to work ourselves to the numerous other topics later on. This will be an introductory and will add onto this thread more as some may need a little more detail on certain topics. If you have any other ideas please feel free to leave a comment but this will not be the Q&A section that was designated as such and this will just be the knowledge portion.
Let us start off with some basics the atmosphere with the multiple layers, as many know we live in the troposphere this is where all of our weather exists. In the picture above (1A) you can see that this goes from the sea surface up to about 11km, lower in the Arctic/Antarctic ~8-9km versus higher in the Tropics reaching to about 13km, for our interests in the mid latitudes. At this point we see changes in the atmospheric composition and a rise in the temperature signifying we have entered into a new region known as the Stratosphere. This region goes from about 11km- 46km (give or take); in this portion of the atmosphere is the ever important Ozone layer. Above this we have the mesosphere where we see the next temp change and then the thermosphere. In the thermosphere there are two key partitions if you will, the ionosphere and exosphere, just at the top edge or embody the upper thermosphere. This is where a lot of the Aurora takes place and the exosphere is the last portion before reaching space. Let us bring it down to the troposphere though at standard sea level pressure you will see one value but different pressure readings, 1013.25mb=1013.25hPa=29.92 in Hg= 101325 Pa they are all the same value just different ways of showing pressure. Pressure in the atmosphere is logarithmic so by the time you reach up to about 500mb, where most of our upper level highs and lows are located, is half of the atmosphere so that by time you reach the top of the troposphere nearly 90% of the atmosphere is below you; this can be seen in the pressure map above(1B). From the Meteorology Today the composition is listed as follows: Nitrogen= 78.08%, Oxygen=20.95% as the two main gases with trace gases of Argon, Neon, Helium, Hydrogen, Xenon, Water Vapor (which varies due to differences in weather and location), Carbon Dioxide, Methane, CFC (Chloroflurocarbons), and Nitric Oxide. The two main trace gases we tend to look at are CO2 and Water vapor, methane is understood but not as widely monitored with changes as CO2 and water vapor. These are GHG’s that are important for life to thrive on the planet. Imbalances can and do occur with the many changes we are currently seeing with CO2 hitting around 410ppm (parts per million) and evaporation rates increasing across the oceans we are seeing large climatic changes occurring. This though can be discussed further in other sections.
There are three different ways that we see the transfer of energy in and throughout the Earth system: Conduction, Convection, and radiation (shortwave and longwave). These mechanisms are responsible for transferring heat and help with the warming of the lower atmosphere with radiation (solar radiation) being the largest proprietor of the warming and the other two mechanisms mainly being a transfer or re-positioning if you will of the warmth at the lower levels. There a number of laws and formulas that can be found in the laws/formulas section; since everything emits and absorbs radiation it is an important process by which these laws help you understand the wavelength the energy is emitted and the total potential energy output of an object. Here is the Earth Energy Budget in the form of W/m^2 this is how we warm and maintain temps of the lower atmosphere.
With the radiation entering the system we have multiple outlets it gets absorbed by vegetation, different materials (rocks, sidewalks, oceans, etc) at the surface as well as animals, mammals, and other creatures. In a perfect system incoming radiation would equal outgoing radiation but we have the GHG’s that help secure some of this energy at the surface. The energy from all this helps moderate our surface temperature to an average of 59F (15C) for the Earth as a whole with areas in the far north/south cooler and near the tropics warmer. A general temp curve with solar max and mins looks something like this:
You receive variation in temps across the globe due to a number of factors but the biggest being the tilt of the Earth to which the sun angle is present, which gives us our seasons. The further north you go the larger the extremes in temperature become since you go through periods of time with either little to no sun, at 60N/S to the poles, in the winter and during summer experiencing sun all day. More local factors tend to be vegetation cover, moisture content of the air, type of soil, proximity to a body of water, etc. As we move through the day the sun does work on the system heating it up and causing a temp profile that can resemble one of these two variations in the lower troposphere, can also be different but these are the two more common modes:
Windy days you can completely mix the lower levels (boundary layer) and have a temp profile sometimes the same temp through a large portion of the column or when you have clear calm days you get a more logarithmic look to the temp curve. This can also be replicated at nighttime as well instead the lines bend backward as you get more cooling at the surface then aloft. The process of cooling the lower levels faster than aloft is known as an inversion. Many locations experience an inversion at multiple times throughout the year, a lot of us in the east tend to see inversions setup on the clear autumn nights and during our east coast storms two different processes but still inversions.
From here we see how the atmosphere is setup from bottom to top with a focus on the troposphere, we see the influences of radiation on the lower atmosphere and how it affects temperatures. Now let us take a focus on how weather systems come about. Boundaries are key in talking about the formation of the many storms we see in winter/summer. The basic earth circulation pattern is as such:
Here we see the wind pattern that sets up from the three different atmospheric cells (Hadley (tropics), Ferrel (mid latitudes), and the Polar cell). Low pressures and rising air near the equator fan out into the horse latitudes (~30N/S) there we have descending sinking air and high pressure; as we move further north and south we continue the pattern with low pressure and rising air around 60N/S and finally descending air/ high pressure at the poles. We then start to evolve a more intricate surface pressure pattern due to these variations in the cells as you go north and south from the equator. The bending/turning of the arrow/winds is due to coriolis forcing with the earth going in a direction from west to east, in the northern hemisphere things get deflected to the right and in the southern hemisphere to the left. It gets tricky due to position and direction you are facing but this is the general idea. Trust me it boggles the mind a little based on perspective of the individual. We see the development of these surface pressure structures due to location of land masses and bodies of water playing a large influence.
How do the surface and upper level pressure patterns come about? Well a lot of this has to do with the overall circulation patterns we had mentioned earlier from the three cells. In between the cells are jet streams, regions of locally channeled air due to temperature differences as you move north/south of the equator. These jet streams are locally responsible for pushing through different weather patterns/ storm systems. There are two different jet streams in which play large parts in our sensible (everyday) weather one being the subtropical jet and the other the polar jet, sometimes there is a third jet (arctic jet) but that doesn’t come into play as often as these two, at least in the mid latitudes, and very rarely does polar and even subtropical influence the tropics. The jet forms, as mentioned above, due to temperature differences in between the two cells with the jet strength being a function of the temperature differences across the area.
The jet stream becomes localized as areas of energy within the flow help carve out a general trough and ridge pattern. The jet itself can be quite difficult to fully understand but here is a schematic of the basic jet structure, think of it as a 3D oblong sphere, almost like a football, where you have jet maxima and then as you go out in all directions you lower the winds speeds. In your jet structure you have an entrance (left in schematic) and an exit (right in schematic) region. To break it down into further sections we draw down the center in both directions of the jet maxima. In the entrance area you have a left and right, left being the convergence and right being the divergence regions and the exit is just the opposite so left would be the divergence region and right convergence. In areas of convergence aloft you will have air pushing together causing sinking of air or NVA (negative vorticity advection) and areas where you have diverging air aloft so air must rise to replace this you have PVA (positive vorticity advection). Well since you have air motion in these regions the air has to come from or go to somewhere and it happens to be the lower troposphere. I highlight aloft in this section because it is important to note this is an occurrence that takes place aloft there are different processes that occur at the surface from the same convergence and divergence.
To add to this when you get strong upper level divergence and weak low level convergence you have the ability to strengthen the low pressure system at the surface. You have strong low level convergence but weak upper level divergence you will weaken the system as there is not the extra added removal and thus lift for the system. If you have both equally strong or equally weak low level convergence and upper level divergence the system tends to remain in a steady state and not much weakening or strengthening will occur. For high pressure systems this also remains similar in the idea. If you have strong upper level convergence and weak low level divergence you can strengthen the high. If you have weak upper level convergence but strong low level divergence you will have a weakening high pressure system. Finally with both upper level convergence and low level divergence being both strong or both weak the high pressure system will remain in a steady state.
Aloft creates the conditions that the lower atmosphere then follows. In areas of upper level convergence you tend to get descending air and building of pressure at lower levels causing a high pressure system at the surface with areas of divergence aloft you tend to get lifting so air rises from the lower levels creating a lower pressure and thus our low pressure system begins to form. One thing of note in these schematics is the tilt that occurs from surface to aloft where at the surface we start out to the right of the upper level trough or ridge and tilt left into the upper atmosphere. This is important in storm formation and high pressure formation; if things become vertically stacked we have a stagnant slow moving pattern, stuck pattern, as everything is being pushed along at the same speed if at all unless disrupted by energy from incoming troughs with the flow of the jet stream or begins to break down as the weather constantly wants to bring itself into balance.
Fronts/ Air masses/ Low Pressure formation
So as we move from aloft to see how pressure patterns at the surface take shape it is important to note that where these systems come from/originate at plays a huge role in what type of weather we see. There are 4 main regions of weather origination cP/cA, mP,mT,cT. cP/cA continental polar and continental arctic is when you have origination taking place over the continent in a colder region this is mainly a thing we see in the U.S. when we have air the plunges down from Canada and the arctic the weather tends to be dry and cold to sometimes extremely cold. mP is maritime polar so origination still in a colder part of the world but more so over a water basin tends to have cool, damp conditions with it many of times when we get low level flow in the east this is the type of air mass we see. mT is maritime tropical again since it is maritime it is formed over a water basin but with a tropical/warm temperature regime, in the east we tend to see this with the Bermuda high that pushes in and bathes us in high moisture content and warm temperatures. Lastly cT is continental tropical this air mass originates over land usually in arid or even desert like conditions we see this take place in the SW U.S. where temperatures can be warm to excessively hot with little to no moisture in the air mass. In between these air masses we have clashes and thus we tend to get our storm systems/low pressures that form.
Now looking at the surface again in between these air masses we have boundaries that setup these boundaries we know them as fronts there are several different types of fronts such as cold front, warm front, occluded front, dry line, stationary front, etc. For this purpose we look at an idealized situation of a boundary where we having clashing air masses one side cold with winds out of the north and northeast and the other side warmth with a south or southwest wind; moisture content is variable within the air mass and applies to where the air masses originated. In this case we have a stalled boundary that sets up as energy/vorticity aloft collocates itself over this boundary with jet interaction we start to see the process unfold.
This process is known by many meteorologists as the Norwegian cyclone model as most storms tend to form in such a manner.
This will be all for now we may add more information as we get things situated and others have questions about certain processes. We have learned how the atmosphere is portioned, what is in the atmosphere, radiation impacts in the atmosphere, basic Earth cell functions in the atmosphere, jet understanding, and storm formation.
Professor Dr. Yalda Met 101 notes I have her information if someone would like to contact.
I will edit to add credit to meteorology today for a good chunk of the pictures.
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