Vertical cross sections at latitudes 15° S, 25° S and 35° S, across the smoke plume contribute to depict the distribution of the meridional transport of PM2.5 (in pgmUs-1) (Figure 10) and water vapour mixing ratio (in gmkg-V1) (Figure 11). The cross-sections clearly illustrate the role of the SALLJ as a transport mechanism. In general, the meridional transport of PM2.5 is limited to the layer between the surface and 4000 m and the higher values are near the emission sources. In the case of the water vapour the vertical extent is greater, reaching 8000m.

At 15° S (Figure 10a), on 23 August, the meridional flux of PM2.5 was mainly southward and on the layer between 1000 and 4000m, with the maximum located between 1500 and 2000m with values between -60 and -180 pgmrV1. The transport was on a narrow region east of the Andes range, centred at 65° W. During the following day, the level of maximum meridional transport was closer to the surface and the longitudinal extent increased. The values were similar than those on the previous day. On 25 August, two relative maxima were present, one close to the surface at 65° W and the other one between 1500 and 3500m above the ground at 62.5° W, ranging from -60 to -300 pgmUs-1. During the following day, the conditions were almost similar, but the maximum close to the surface weakened. During 27 August, the southward transport east of the Andes was comparable, ranging from -180 to -240 pgm-2s-1 and a secondary maximum west of the mountain range near 3000m was present. On 28 and 29August, the southward transport was mainly in the layer between the surface and 3000m, with a longitudinal extent from 72.5° W to 55° W. The maximum values varied from -240 to -360 pgm"2s_1. A narrow elevated maximum occurred, at upper levels and 40° W. On 30 August, the southerlies reached this latitude, and a northward transport occurred near the surface from 65° W to 50° W with values between 80 and 120 pgm-2sA The southward transport persisted at upper levels close to the Andes, but gradually vanished according to the cold front movement. During 31 August, the northward flux near the surface prevailed, ranging from 80 to 140 pgm-2sA

At 25° S (Figure 10b), on 23 August, the meridional flux showed a maximum of -120 pgm-2s_1 centred at 60° W. The next day the maximum flux occurred westward, at 62.5° W and ranged from -120 to -240 pgm-2sA During 25 August, the location was similar and the values increased, varying from -180 to -360 pgm-2s-h On the following two days, one region of maximum transport was located close to the Andes from surface up to 3500 m, with values that ranged from -300 to -660 pgm-2s_1 and the second one, was near the surface centred at 57.5° W, varied from -60 to -180 pgm-2s_1 and spanned ten degrees east of 65° W.

During 27 August, there is also a transport towards the south between 3000 and 4000m west of the Andes. The next day, the transport had similar longitudinal and vertical span and values from -360 to -600 pgm-2s_1. By 29 August the southward flux was -180 to -600 pgm-2s_1 between 62.5° and 50° W and the northward transport was centred at 60° W, ranging from 60 to 260 pgm-2s-h During 30 August the northward flux occurred between 63° and 50° W and values from 20 to 60 pgm-2s_1 and towards the south in upper levels at 47° W ranging from — 180 to -80 pgm"2s_1. The last day of the studied period had very light northward transport smaller and equal than 20 pgm-2s-1, and southward flux in upper levels from 45° to 40° W with a maximum of -60 pgm-2s-h

Figure 10c illustrates the PM2.5 meridional flux at 35° S. The southward flux started on 24 August, the plume was near the surface between 60° and 50° W, with values from -60 to -120 ^gm-2s-1.

Fig. 10b. Vertical cross-sections at 25° S of PM2.5 meridional transport (pgm’2s-1) against the height above the surface. Terrain height profile is included.

During the next day, two maxima appeared, one located near the surface and the other one centred at 2000m and values ranging from -60 to -120 pgm-2s-1. During 26 August, the upper
level maximum, centred at 2500m and east of 60° W strengthened, the values ranged from — 60 to -360 pgm-2s-1. On 27 August the southward transport was widespread and ranged from -60 to -420 pgm-2s-1. On the following day, the smoke transport extended up to 5000m, remaining towards the south and east of 60° W and the maximum values ranged from -60 to -360 pgm-2s-h Close to the mountains a northward transport occurred near the surface, with values between 20 and 100 pgm-2s_1. By 29 August the plume was over the Atlantic Ocean and the northward transport was west of 55° W, ranging from 40 to 60 pgm"2s_1. During the next two days the flux gradually disappeared at this latitude due to the fast movement of the cold front.

rv meridional flux — 15 S 25AUG2002 rv meridional flux — 15 S 2BAUG2002

Fig. 11a. Vertical cross-sections at 15° S of water vapour mixing ratio meridional transport (g m kg-1 s-1) against the height above the surface. Terrain height profile is included.

Figure 11 shows the vertical cross sections at similar latitudes, but illustrates in this case, the water vapour meridional transport. At 15° S (Figure 11a) on 23 August there was a prevalence of the southward transport of water vapour, spanning from 72.5° W to 47° W, from the surface up to 3000m, and the maximum flux centred at 1500m with a mean daily value of -60 gmkg-1s_1. The northward transport took place over the oceans near the surface. The next day the pattern was similar and the value of the meridional flux increased. On the following three days the longitudinal extent of the zone with southward flux was narrower and the values -80 and -60 gmkg-V1 respectively. West of the Andes, at upper levels the water vapour southward flux also occurred. The northward transport over the oceans was still present. On 28 and 29 August the longitudinal extent increased as well as the value of the maximum flux, the difference is the location near the surface. The northward water vapour transport increased over the Pacific Ocean. During 30 August, the incursion of the cold front caused a northward flux near the surface between 65° and 50° W. The flux from the north was restricted next to the Andes centred at 1000m. The following day the pattern was nearly similar, with a decrease in the southward transport.

At 25° S (Figure 11b) from 23 to 28 August, there was a southward flux at all longitudes east of the Andes from the surface up to middle levels in the troposphere.

rv meridional flux — 25 S 25AUG2002 rv meridional flux — 25 S 26AUG2002

Fig. 11c. Vertical cross-sections at 35° S of water vapour mixing ratio meridional transport (g m kg-1 s-1) against the height above the surface. Terrain height profile is included.

The values ranged from -140 to -260 gmkg^s-1. West of the mountain range, the southward flux also occurred on 26 and 27 August reaching a daily maximum of -80 gmkg-1s-1. From 29 to 31 August the progression of the cold front caused a northward flow that varied between 20 and 120 gmkg-1s-1 with a longitudinal range that moved to the east.

Figure 11c depicts the water vapour meridional transport at 35° S. The southward water vapour transport was present from 23 to 27 August from the surface up to 8000m and 75° W and 35° W, the maximum values varied from -100 to -260 gmkg-1s-1. The opposite transport directions associated with the surface cold front is sharply marked in the cross-sections on 28 and 29 August, and the maximum values are located near the surface. The next days showed the contrast in the air masses water vapour as well.