Three-dimensional Structure in Midlatitude Cyclones. ATMS 370 Due Friday, March 9, 2018

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1 Three-dimensional Structure in Midlatitude Cyclones ATMS 370 Due Friday, March 9, 2018 In this lab, we exam a cross-section for a case that occurred in January 1996 and use backwards calculated trajectories to explain the features that are evident in the cross-section. The supported figures are all posted on the web on our class web page: Scroll down to Trajectory Lab Links. There are trajectories, text files from the trajectory model runs, and figures made from GARP. At the end of this assignment, there are also instructions for using GARP yourself in case you want to look at other fields I didn t provide. A black and white version of the cross-section and a copy of the operational surface map is given in this homework and also is posted on the website. Important Notes about the Trajectories Each graphic is a set of trajectories that all end along the line of the cross-section and at a specific pressure level (i.e. they end at 850 hpa, or at 700 hpa, etc.). You can tell the pressure level they end at by the file name which shows up in the window at the top of the loop. Both the color coding of the trajectories and the text output tell you the pressure level along the trajectory and its geographical position. Use these together to figure out the path each parcel took and whether it was a rising or sinking parcel. Each trajectory corresponds to EVERY OTHER sounding in the cross-section. The furthest west trajectory is at DDC and the furthest east trajectory is at GSO, and the ones in between correspond to every other sounding between these two stations. The text files give you information that looks like: UNITS: SPD-knots OMG-microbars/sec DD TT LAT LON PRS DIR SPD OMG The first two columns are the date and time of the parcel, going backwards in time, then the latitude and longitude of the parcel, then the pressure level. The last three columns are the direction, speed and vertical motion (in terms of omega) of the parcel. When omega is positive, that is sinking motion, negative is rising motion. This is the text output that corresponds to the graphical output. The first parcel listed is the one furthest west, followed by the adjacent parcel to the east and so on.

2 Overview of cross-section 1. The cross section goes from Dodge City, KA (DDC) to Greensboro, NC (GSO). Look at the satellite image, the satellite image with sea level pressure overlaid and the satellite image with 300 hpa isotachs overlaid. What features does this cross-section intersect (surface fronts, jetstreaks, clouds, etc.)? Cross-Section features 2. On the black and white cross-section provided (you can use the color version online to help you), shade with colored pencils, the following items: a. Regions of cold and/or warm air advection (use the turning of the winds with height) b. Regions of strong horizontal temperature gradients c. Regions of high humidity 3. On the cross-section, indicate the positions of the following: a. The cold front b. A strong upper-level humidity gradient (look above 700 hpa) Low-level features Instructions Look at the loop of the trajectories and stop at the 850 hpa trajectories Open another browser window and loop the GARP graphics and stop at the map with 850 hpa heights, temperature and relative humidity at 00 UTC 27 January Compare and contrast the nature of the trajectories that end west of the cold front (postfrontal trajectories) to the trajectories that end east of the cold front (pre-frontal trajectories). Describe features that include the origins of the parcels, the vertical motion experienced by the parcels, and the resulting relative humidity. Use the surface map provided and the 850 hpa map created in GARP to help you put the trajectories in perspective. Draw a rough sketch of the trajectories ending at 850 hpa grouping together trajectories with similar pathways and indicate their location with respect to the model frontal position. 5. Look at the trajectories that end at 700 hpa and the 700 hpa heights, temperature and relative humidity map from GARP. There is a region of low relative humidity in the middle of the cross-section at 700 hpa. How do the trajectories differ within this region compared to the rest of the trajectories ending along 700 hpa? Upper-level features Look at trajectories that end at 500 hpa and 300 hpa and the 500 hpa GARP graphic. 6. Compare and contrast the nature of the trajectories that end on each side of the upperlevel humidity gradient you highlighted in question #2 above. Include features such as the origin of the parcels and the vertical motion experience by the parcels.

3 Satellite features Instructions Look at the satellite image in one window and the trajectories that end at 850, 700 and 500 hpa in another window. 7. Relate these trajectories to the cloud pattern evident in the satellite image. What are the origins of the parcels that end in the cloud regions? Dry regions? What are the vertical motions experienced by these parcels in these regions? 8. In lecture, three types of airstreams were described, the warm conveyor belt, the cold conveyor belt, and the dry sinking airstream. Are these three airstreams present in this case? Cite your supporting evidence. *** OPTIONAL *** Instructions for GARP To make your own version of the cross section do the following: Type garp_jan96-new. To create a cross-section (6 th button) doing the following: Select the NGM model (default is ETA). Have the cross-section go from Dodge City, KS to Greensboro, NC: ddc>gso Plot Theta_K using a contour interval of 2.5 (using the more button). Plot Wind, using the more button to plot wind barbs (not arrows) Plot relative humidity, RelHum%, select the color fill option, then the regions of high humidity are shaded. To make your own maps, use the NGM model, and note, to plot sea level pressure you ll need to do the following Select MSLP mb Edit PMSL%NONE@0 to read PMSL%PRES@0

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