US EPA

3236299 

Journal Article 

Formation mechanisms for convection over the Ligurian Sea during MAP IOP-8 

Lin, YL; Reeves, HD; Chen, SY; Chiao, S 

2005 

1 

Monthly Weather Review
ISSN: 0027-0644
EISSN: 1520-0493 

133 

8 

2227-2245 

WOS:000231250500008 

The dynamical impacts of an unusually strong stable layer
that developed over the Po Valley and northern Ligurian Sea during Mesoscale Alpine Program (MAP)
intensive observation period 8 (IOP-8) on the formation of convection over the Ligurian Sea are
explored. Based on numerically simulated equivalent potential temperature, wind vectors, and by a
trajectory analysis of parcels both beneath and above the stable layer, it is shown that the
stable layer behaved as a material surface or ""effective mountain"" to the airstreams impinging
on it from the south. Additional analyses show that the leading edge of the stable layer was
collocated with maxima in upward motion and a strong positive moisture flux. Hence, it was
further argued and demonstrated through inspection of soundings upstream of the cold dome and
trajectory analyses that lifting by the stable layer enhanced convective activities over the
Ligurian Sea. Finally, processes contributing to the maintenance of the stable layer during IOP-8
were explored. It was found that the differential advection of a warm, less stable air mass on
top of a cooler, more stable air mass helped maintain the stable layer. The Ligurian Apennines
made a secondary contribution to the stagnation of the cool air in the Po Valley by partially
blocking this air mass from exiting the valley to the south.