TEAM 2

Sanders & Li

295K

300K

305K

310K

295K

300K

305K

310K

900mb

850mb

Map Synopsis

The isentropic analysis clearly depicts areas of rising and descending motion. Rising motion is seen on the isentropic analysis in the southern U.S. just to the north of the Gulf of Mexico. Rising motion can also be seen over northern New England. This is evident in the GARP figures where the wind is crossing the pressure surfaces from high pressure to low pressure. The visible satellite image supports this theory because there are clouds where rising motion is occurring. The GARP figures also depict areas of descending motion. This is occurring where the wind is crossing the pressure surfaces from low to high. In these areas of descending motion the satellite image depicts no clouds. Such a processes is occurring through the Mid Mississippi River Valley and eastward through the Ohio River Valley. The rising and descending motion is seen best on the 300 K level although it is visible on the levels just above and below this. The GARP figures containing the RH fields further support this notion. The RH is greatest where rising motion is taking place and least where descending motion is occurring. It is interesting to note that the RH is greater on the 295K surface than at higher levels. This means that the moisture is at lower levels.

The 900mb and 850mb maps further support this notion. WAA is seen on the pressure map in the southern U.S. just north of the Gulf of Mexico. This is the same location that the isentropic maps depicted rising motion. CAA is occurring on the pressure maps over the regions were descending motion was occurring on the isentropic maps. The level of the moisture also corresponds between the pressure and isentropic maps. There is more moisture in the 900mb and 295k maps than there is in the 850mb and 305k maps. This clearly demonstrates that these two types of maps are showing the same information but just in a different manner. In the 900mb map there is a dry area in the Gulf of Mexico, but on the 295K map the same area has high RH. This is because the isentropic map actually goes down in the altitude as we go south, where there is more moisture than above.

Air is ascending from 1000mb to the 850mb surface. This is a vertical distance of roughly 1.6km and occurs from SW IL to NE IL. Air is descending from 420mb to 850mb over a vertical distance of 5.5km over MT to SE SD. In the WAA pattern air will continue to rise roughly to 550mb. In the CAA pattern air will fall until it hits the surface. The isentropic analysis shows that the RH in lower levels of the atmosphere is quite low, between 40% and 60% at 900mb. This means at the surface the RH will be even lower. Even at high levels, above 600mb, the RH is just above 80%. Not much precipitation will be produced by this system because any precipitation in the upper levels will evaporate before it hits the ground. We will probably see a lot of virga on the radar as this system passes over the Great Lakes.

The wind on isentropic surface is close to geostrophic wind, which means that even when air is ascending or descending, there is not much dynamic forcing in the synoptic scale, the movement of the air parcel is largely in geostrophic balance.

The wind on 850mb is just the wind at that pressure level. On the isentropic map the wind follows the movement of air parcel.