Download Cold Air Damming Group 1

Cold Air Damming Group 1 1. There is a pronounced ridge axis located to the east of the mountains, with a trough axis located to the west of the mountains. Towards the southern and eastern extent of the ridge axis there is a strong area of frontogenesis along the edge of where the cold air is located. This area of frontogenesis is located in “kinks” of lower pressures in the pressure field, which indicates there is a front located at the edge of the CAD east of the mountains. This is likely a result of a backdoor cold front sent south from from a high pressure located over New England. This front has since stalled and is now likely a stationary front...located along the coast of NC/SC and inland through central GA. 2. Term A: We see that d(theta)/dx (the along front temperature gradient) is near 0 along most of the front, therefore this term is negligible. Term B: d(theta)/dy is always negative. dv/dy is also negative because winds go from positive to negative in the +y direction. This means that this term is acting frontogenitically. Term C: Since this is surface frontogenesis, omega is near 0, so d(omega)/dy is 0, which makes this entire term negligible. Term D: We see that there are clouds located over the CAD region (via mid level RH) and there are none outside of this area. That makes this term frontogenetical. So term B and term D are the dominant terms in this situation. 3. Throughout the period up until 00z on 02/17 a high pressure builds east into New England. At the same time a low pressure was seen moving northeast towards the mid­Mississippi river valley. As the high pressure builds east into New England, we see that winds begin to turn from the NE over of the Carolinas and mass begins to build up along the mountains...noted by the building ridge. This ridge extends into the Carolinas and Georgia by 00z on the 17z. Also noted was a trough that was deepening west of the mountains as the ridge builds on the eastern side. The area of low pressure moved to the ENE and began to dissipate as it encountered the mountains. Shortly thereafter, the low pressure redevelops to the SE closer to the coastline east of the mountains and CAD. 4. The southward moving component of the air in the NE flow over the Carolinas from the high pressure over New England causes the coriolis force to move the air to the right...in this case towards the mountains. This causes a buildup of mass to the east of the mountains which results in higher pressures and a ridge forming. To the west of the mountains, the coriolis force acts torques the air away from the mountains, creating a minimum in mass and troughing here. Since the mountains block the cold air, the cold front and its associated frontogenesis tends to create a backdoor cold front that extends along the coast and also along the southern extent of the cold air east of the mountains. This front marks the boundary between the colder air of the CAD (the colder air banked up east of the mountains) and the relatively warm air over the ocean and to the south. If the mountains did not exist, then the pressure field would not consist of a ridge or a trough since there is no barrier (mountains) to block the movement of air and pile up the mass. It would just show as an average cold frontal passage...or possibly none at all and the cyclone would likely move east without much change in strength. B. 1. In this case there is no ridge axis over the Carolinas and no CAD evident in the surface pressures. This can be seen in the 278k theta surface as well, since there is not a cold dome extending through the Carolinas. This is due to the fact there was no backdoor cold front that moved through the area. Instead the area of low pressure tracked NE with an associated warm front extending to it’s E (noted in the kinks of lower pressure in the SLP and an area of frontogenesis) with a cold front extending to the SW. 2. In the controlled simulation, the mountains allow for the cyclone to dissipate as it moves over the due to the conservation of absolute vorticity (compression of the column and a reduction in the vorticity). As it moves to the eastern side of the mountain the low pressure system is able to reform due to the stretching increasing the relative vorticity. In the simulation without the mountains, there is no compression or stretching of the column to affect the strength of the vorticity and the cyclone and the cyclone is able to move northeast without much change in strength. The presence of the sharp ridge (CAD or cold dome) immediately east of the mountains will prevent the stretching of the column initially. The stretching was more gradual and more pronounced farther east, near the coast which is where the low pressure reforms. 3. In the simulation with the mountains...we see that the low pressure approaches the mountains and begins to weaken. Farther east of the mountains and the CAD...along the coast, the low pressure reforms due to vorticity stretching (east of the mountains and cold dome). A pronounced ridge was present due to the CAD east of the mountains as well. In the simulation without the terrain..the low simply moves off to the ENE and does not vary much in strength. Instead of a sharp ridge over the Carolinas, there is a warm front lifting north associated with the low pressure.There was likely rainfall and clouds with both situations, however rainfall may have been more pronounced with the CAD as the warm SE flow rode up over the cold dome in the Carolinas and Virginia in the simulation with the terrain. Additionally, without the CAD locked in place, temperature would have been much warmer in the simulation without the terrain...east of the mountains, especially after the warm frontal passage.