Strong winds and heavy rains pummeled the North African coast over the period from 9 November 10 to November 2001 in association with the movement of a deep upper level trough over the region from the northwest. Heavy rain fell in the city of Algiers beginning late Friday November 9 and ending near noon on Saturday November 10. Over 100mm of rain fell in a 6-hour period early that Saturday. The rains were accom- panied with strong winds. The heavy rains led to massive flooding killing 737 people in Algeria and leaving 23,000 homeless. This amounted to the worst flooding and second worst natural disaster to hit Algeria since independence in 1962. The unusual weather continued for nearly 48 hours and was associated with strong winds along the Mediterranean coast, and yellow clouds producing heavy dust laden rains in Rome. CNR lidar measurements confirmed the heavy dust presence on 12 and 14 November. In this paper, a high-resolution numerical simulation of the storm is presented. Results show that the storm was preceded by a southward penetration of the jet stream into northern Africa associated with an unusually deep tropopause fold. With the fold was a strong potential vorticity maximum aloft that spawned an intense low-level response producing a strong surge of low-level flow from the north in the western Mediterranean and a strong low-level surge from the south into the south-central Mediterranean north of Libya. It was the northerly flow surge that picked up moisture from the Mediter- ranean and produced the orographic rains and wind affecting Algiers. The southerly surge built northward, producing the strong winds over Rome. The two wind streams together created strong low-level vorticity and together with the moisture drawn from the Mediterranean and convection resulting created conditions favorable of the trop- ical (warm-core) storm genesis. The result was the growth of an intense low-level cyclone with unusually strong winds and tropical characteristics north of Algiers and west of Sardinia that moved northward slowly and persisted into November 11. The event was interesting not only because of the damage suffered, but because of the se- ries of mesoscale and synoptic scale interactions that led to its development including the effects of several mountain ranges, the fluxes of moisture from the water surface and associated deep moist convection, and thermal fluxes from the floor of the Sa- hara desert. Together these events came together to produce 2001Ss most significant weather event. Modeling results depicting how these mesoscale structures evolved will be discussed at the oral presentation.
The 9-10 November, 2001 Algerian Flood: A Mesoscale Numerical Study
Dietrich S;Panegrossi G;Mugnai A
2002
Abstract
Strong winds and heavy rains pummeled the North African coast over the period from 9 November 10 to November 2001 in association with the movement of a deep upper level trough over the region from the northwest. Heavy rain fell in the city of Algiers beginning late Friday November 9 and ending near noon on Saturday November 10. Over 100mm of rain fell in a 6-hour period early that Saturday. The rains were accom- panied with strong winds. The heavy rains led to massive flooding killing 737 people in Algeria and leaving 23,000 homeless. This amounted to the worst flooding and second worst natural disaster to hit Algeria since independence in 1962. The unusual weather continued for nearly 48 hours and was associated with strong winds along the Mediterranean coast, and yellow clouds producing heavy dust laden rains in Rome. CNR lidar measurements confirmed the heavy dust presence on 12 and 14 November. In this paper, a high-resolution numerical simulation of the storm is presented. Results show that the storm was preceded by a southward penetration of the jet stream into northern Africa associated with an unusually deep tropopause fold. With the fold was a strong potential vorticity maximum aloft that spawned an intense low-level response producing a strong surge of low-level flow from the north in the western Mediterranean and a strong low-level surge from the south into the south-central Mediterranean north of Libya. It was the northerly flow surge that picked up moisture from the Mediter- ranean and produced the orographic rains and wind affecting Algiers. The southerly surge built northward, producing the strong winds over Rome. The two wind streams together created strong low-level vorticity and together with the moisture drawn from the Mediterranean and convection resulting created conditions favorable of the trop- ical (warm-core) storm genesis. The result was the growth of an intense low-level cyclone with unusually strong winds and tropical characteristics north of Algiers and west of Sardinia that moved northward slowly and persisted into November 11. The event was interesting not only because of the damage suffered, but because of the se- ries of mesoscale and synoptic scale interactions that led to its development including the effects of several mountain ranges, the fluxes of moisture from the water surface and associated deep moist convection, and thermal fluxes from the floor of the Sa- hara desert. Together these events came together to produce 2001Ss most significant weather event. Modeling results depicting how these mesoscale structures evolved will be discussed at the oral presentation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
