Outflow of winter smog over north Indian Ocean

By HansPeter Roesli (Switzerland)

There was a similar case on 24 December 2010, but this time the outflow occurred over a much longer stretch of the west Indian coastline.

The smog is difficult to detect in infrared imagery, due to very low thermal contrast between the smog and the underlying ocean. However, the much enhanced Natural Colour RGBs from Meteosat-8 allowed for identification of the smog, as shown on the animation between 03:00 UTC and 13:00 UTC (Figure 1).

The comparison between a True Colour RGB from OLCI on Sentinel-3 and a Meteosat-8 Natural Colour RGB around 06:47 UTC (Figure 2) shows a relatively complex structure along the smog front. e.g. the two whirls, the more southern one leading the main front, that temporarily formed off the Pakistani coast (red arrows on Sentinel image).

Even closer to the Pakistani coast the cloud/haze features can be seen moving backwards (in the opposite direction of the front’s displacement, red arrow in Figure 3). This counter motion, occurring above the smog top, can be better seen on the second part of the animation in Figure 1.

The smog outbreak from the east was preceded the day before by a dust outbreak from the north.

The sequence of Meteosat-8 Natural Colour RGBs (Figure 4), shows that Sistan winds drove dust veils into the Sea of Oman and the Arabian Sea off the Iranian-Pakistani coasts.

Winds at the 975hPa-level from the GFS analyses at 06:00 UTC on both days (Figure 5) confirmed the rapid change in the low-level wind field over the area.