Tropical Upper Tropospheric Trough—July 2001
The tropical upper tropospheric trough (TUTT) can play a role in hurricane forecasting, since it is associated with westerly shear and discourages the development of hurricanes. Chris Landsea showed some years ago that the MRF tended to fail to forecast TUTTs well. The operational MRF of July 2001 still appears to have trouble forecasting and maintaining TUTTs, at least in the example shown here. TUTT appears to be a very difficult test of our ability to model the tropical atmosphere.
During July 2001 an anticyclone dominated the upper tropospheric circulation over North America over the central United States to the north and east of its climatological position; a double trough could be seen over the western Atlantic. One trough was near 70W in the analyses, extending south to 15N, but gradually weakened and disappeared in the forecasts; another was initially near 50W to the northeast of the first and shifts to the east in the forecasts.
Monthly mean circulation
140W-0
equator-50N
July 2001
|
850 hPa |
200 hPa |
150 hPa |
|
|
|
|
Forecast errors in monthly mean circulation
Against analyses
140W-0
equator-50N
July 2001
|
850 hPa |
200 hPa |
150 hPa |
Vertical cross-sections at 15N show strong vertical shear at 70W in the analyses that gradually disappears in the forecasts.
Vertical cross-section of zonal wind
140W-0
15N
July 2001
|
Analyses and forecasts |
Forecast errors (against analyses) |
|
|
Longitude-time diagrams at 15N show the presence most of the two months of westerlies at 70W, with some tendency to move westwards; an easterly bias can be seen in the error diagrams. A five-day running mean removes synoptic activity.
Longitude-time diagrams of zonal wind
15N
0-360
Daily values
|
|
||
Five day running means
|
|
||
