Tropical Upper Tropospheric Trough—July 2001

 

Glenn.White@noaa.gov

 

            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

 

1979-98 NCAR/NCEP climatology

 

Analyses and 1 day fcsts

Analyses and 1 day fcsts

Analyses and 1 day fcsts

3 and 5 day fcsts

3 and 5 day fcsts

3 and 5 day fcsts

7 and 10 day fcsts

7 and 10 day fcsts

7 and 10 day fcsts

15 day fcsts

15 day fcsts

15 day fcsts

 

Forecast errors in monthly mean circulation

Against analyses

140W-0

equator-50N

July 2001

 

850 hPa

200 hPa

150 hPa

1 and 3 day fcst errors

1 and 3 day fcst errors

1 and 3 day fcst errors

5 and 7 day fcst errors

5 and 7 day fcst errors

5 and 7 day fcst errors

10 and 15 day fcst errors 

 10 and 15 day fcst errors

 10 and 15 day fcst errors

 

            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)

Analyses and 7 day forecasts

1 and 3 day fcst errors

Analyses and 15 day forecasts

5 and 7 day fcst errors

 

10 and 15 day fcst errors

 

            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

 

1 day forecasts

Verifying analyses

3 day forecasts

Verifying analyses

3 day errors ag. analyses

5 day forecasts

Verifying analyses

5 day errors ag. analyses

7 day forecasts

Verifying analyses

7 day errors ag. analyses

8 day forecasts

Verifying analyses

8 day errors ag. analyses

10 day forecasts

Verifying analyses

10 day errors ag. analyses

15 day forecasts

Verifying analyses

15 day errors ag. analyses

 

Five day running means

 

1 day forecasts

Verifying analyses

3 day forecasts

Verifying analyses

3 day errors ag. analyses

5 day forecasts

Verifying analyses

5 day errors ag. analyses

7 day forecasts

Verifying analyses

7 day errors ag. analyses

8 day forecasts

Verifying analyses

8 day errors ag. analyses

10 day forecasts

Verifying analyses

10 day errors ag. analyses

15 day forecasts

Verifying analyses

15 day errors ag. analyses