Atm Ocn 100 Edition 1nd Lecture 17 Outline of Last Lecture I Review for the test a Study Guide questions Outline of Current Lecture II Current Weather III Cumulonimbus IV Thunderstorms V Precipitation process in a Cumulonimbus VI Wind Shear VII What causes a thunderstorm to form Current Lecture Current Weather There is a Bermuda tropical cyclone going on right now We can see the eye in the area of green coloring It doesn t look quite as impressive as it did yesterday There s a pressure of 947 MB Seems like this is an El Nino year storms do not form in the Atlantic as readily There is an overall suppression sinking motion in the Atlantic from the El Nino There is no official El Nino yet but it looks like it is occurring This season has not been a great season in the Atlantic for tropical storms But there have been a lot of storms in the Eastern Pacific Now there is one going on in Hawaii Storms in the Mid Pacific are quite unusual We can see even in El Nino season s storms that approach Hawaii Reminders Homework 3 due tonight by 11 59PM Homework 4 Due Friday October 31 2014 TYU Ch 20 1 3 4 7 20 TYPSS 3 TYU Ch 21 1 5 6 9 11 TYPSS 2 TYU Ch 22 1 2 3 4 TYPSS 3 Cumulonimbus A cumulus cloud which has produced precipitation Updrafts rise to equilibrium level often the tropopause Forms in an environment of conditional instability Extra notes Nimbus the word comes from the meaning of dark base The dark base indicates shadowing on the cloud this is from the sunshine on the top which doesn t penetrate through A thick cumulonimbus is one that will have precipitation it will have a darkened based Some cumulous s don t reach the tropopause Not even half will reach it around the world Cumulous clouds always form in conditional unstable environments Conditional instability is when a parcel is only unstable in the case of being unsaturated this can build so if it a parcel isn t saturated the parcel can remain in a stable configuration And then you can make it more and more conditionally unstable without making it unstable The way conditional instability is built is by increasing the moisture If there is gulf moisture it could be building conditional instability without releasing it This can also happen by increasing temperature Conditional instability in the afternoon can be greater then in the morning If the potential temperature of the air is warmer then the temperature above it will overturn But if you keep putting moisture all the way up to saturation before a parcel or the environment becomes unstable this allows for a big production of conditional instability If warm air is rising then cold air is sinking warm air doesn t realize its warm air until it s saturated Air can build up a lot of conditional instability and then rise and become big thunderstorms and cumulonimbus clouds As we know from prior lectures this process requires something to push the air up to a point which then protects the environment from overturning and allows it to build large instabilities Graph from Miami This graph sounding depicts the buoyancy of parcel temperature and environmental temperature If we add all of the area up between the parcel path and the environment it would equal the area of the total amount of energy available for CAPE The graph shows parcel path parcel temperature etc Equilibrium is where a parcel would rise along moist adiabatic It is a point at which the path intersects again with sounding it the parcel went beyond this point it would keep rising but then be colder than the environment so it would fall back to its original place Because of this air parcels rise to this equilibrium level and then stay there and spread out This is then what creates thunderstorms The CAPE as we have discussed before is between the temperature and the parcel path You can measure CAPE in joules The bigger the area the stronger the updraft of the cloud would be Thunderstorms In the picture we are looking at the anvil has reached the tropopause The anvil is the horizontally extended upper part of a cumulonimbus cloud Thunderstorm is considered the whole entity It is composed of smaller parts as well which are cells A cell is an individual updraft pushing up there are new ones that are coming up on the left There is a sinking motion that is associated with that Newer cells are being formed to the left Cells form within a thunderstorm they are individual cells For this particular picture we are looking at a multicellular thunderstorms which means it has many individual cells The lifetime for an individual cell ranges from 20 minutes to a half hour The entire thunderstorm can keep forming new cells on one side and the whole thunderstorm may last for hours When precipitation falls to the ground it cools the air This is from the evaporation of precipitation Opposite of the process in which air raises and is heated this process involves sinking currents with precipitation which then will cool the air through the evaporation of precipitation This is reverse of condensation This is taking heat out of the air And in that sense it cools the air and than the cool air produces a front called a gust front As the gust front moves it pushes air up The cooling effect or cool air produces new cells on the downshear side of the cloud Downshear is a wind shear that occurs in the direction of the upper level wind compared to the lower level wind Wind shear is the calculation of upper level wind minus the lower level wind Downshear will have some wind momentum of the wind shear Air will push left and lift air that then produces new cumulus cells Overall a thunderstorm survives underneath warm air because new cells form and then there is a discontinuous pulsing process This is an example of a multicellular thunderstorm which most thunderstorms are Thunderstorm A thunderstorm is a group of one or more cumulus cells supporting a common density current cold pool at the surface and a common anvil Technically a thunderstorm should have lightning which occurs in a cumulonimbus cloud when ice is present A thunderstorm is a type of cumulonimbus Types of thunderstorms Pulse or air mass thunderstorms These are short lived single celled cumulonimbus having a lifetime of about 20 minutes Multicell Thunderstorm These are a grouping of more than one cumulus cell in succession or simultaneously organized around a common density current Supercell Thunderstorm This is a thunderstorm system organized around a single long lived dominant cell Subsidiary