4:30 PM - 4:45 PM
[MIS21-05] A Vortex-Vortex Interaction as the Maintenance Process of a Cutoff Low: A Case of July 2021 in Europe
Keywords:cutoff low, eddy kinetic energy, trajectory analysis, maintenance process, diabatic effect, cyclonic-anticyclonic asymmetry
Heavy rainfall and flood seriously damaged Central Europe from July 12 to 15, 2021, resulting in more than 200 fatalities. A maintained cutoff low over there is thought to be one of the causes of the disaster. This cutoff low (hereafter ‘C1’) forms through a cutoff of a deepened trough around July 11 and lasts distinctly up to around July 19. C1 merges with another cutoff low (hereafter ‘C2’) around July 12 and experiences a second cutoff around July 14.
First, we analyze eddy kinetic energy inside a fixed area surrounding C1 for a few days including the period July 12 - 14. It is found that C2 supplies energy to C1, which contributes maintenance of C1 after its second cutoff. Second, we calculate three-day backward trajectories (from 00 UTC July 14 to 00 UTC July 11) of tracers inside C1 at 00 UTC July 14. Approximately 12 % of the tracers are from C2 and have high potential vorticity (PV) values. They show significant decrease of PV valued compared with counterparts that stay in C1 during the calculation period. The timing of noticeable decrease of the high PV values corresponds with when tracers flow from C2 into C1, which supports strong diabatic effects work especially during the inflow. We then calculate three-day forward trajectories (from 00 UTC July 11 to 00 UTC July 14) of tracers inside C2 at 00 UTC July 11. Some of them flow into C1 from the northwest and move counterclockwise along its edge. Last, we quantitatively diagnose classification and spatiotemporal distribution of the diabatic effects above along them by using first-guess forecast values.
These results uncover C2 is an important energy source for maintenance of C1 in terms of a vortex-vortex interaction, while diabatic effects should not be ignored. In the meeting, we will also discuss the asymmetry between these results and the maintenence process of anticyclonic (i.e., high pressure) systems proposed by precede studies.
First, we analyze eddy kinetic energy inside a fixed area surrounding C1 for a few days including the period July 12 - 14. It is found that C2 supplies energy to C1, which contributes maintenance of C1 after its second cutoff. Second, we calculate three-day backward trajectories (from 00 UTC July 14 to 00 UTC July 11) of tracers inside C1 at 00 UTC July 14. Approximately 12 % of the tracers are from C2 and have high potential vorticity (PV) values. They show significant decrease of PV valued compared with counterparts that stay in C1 during the calculation period. The timing of noticeable decrease of the high PV values corresponds with when tracers flow from C2 into C1, which supports strong diabatic effects work especially during the inflow. We then calculate three-day forward trajectories (from 00 UTC July 11 to 00 UTC July 14) of tracers inside C2 at 00 UTC July 11. Some of them flow into C1 from the northwest and move counterclockwise along its edge. Last, we quantitatively diagnose classification and spatiotemporal distribution of the diabatic effects above along them by using first-guess forecast values.
These results uncover C2 is an important energy source for maintenance of C1 in terms of a vortex-vortex interaction, while diabatic effects should not be ignored. In the meeting, we will also discuss the asymmetry between these results and the maintenence process of anticyclonic (i.e., high pressure) systems proposed by precede studies.