A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima
This paper investigates the formation and evolution of deep convection inside the east–west oriented rainbands associated with a low-level jet (LLJ) in Typhoon Morakot (2009). With the typhoon center to the northwest of Taiwan, the westerly LLJ occurred as a result from the interaction of typhoon ci...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2015-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/15/11097/2015/acp-15-11097-2015.pdf |
| _version_ | 1811193192902557696 |
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| author | C.-C. Wang H.-C. Kuo R. H. Johnson C.-Y. Lee S.-Y. Huang Y.-H. Chen |
| author_facet | C.-C. Wang H.-C. Kuo R. H. Johnson C.-Y. Lee S.-Y. Huang Y.-H. Chen |
| author_sort | C.-C. Wang |
| collection | DOAJ |
| description | This paper investigates the formation and evolution of deep convection inside
the east–west oriented rainbands associated with a low-level jet (LLJ) in
Typhoon Morakot (2009). With the typhoon center to the northwest of Taiwan, the
westerly LLJ occurred as a result from the interaction of typhoon circulation with
the southwest monsoon flow, which supplied the water vapor for the extreme
rainfall (of ~ 1000 mm) over southwestern Taiwan. The Cloud-Resolving
Storm Simulator with 1 km grid spacing was used to simulate the event, and it
successfully reproduced the slow-moving rainbands, the embedded cells, and
the dynamics of merger and back-building (BB) on 8 August as observed. Our
model results suggest that the intense convection interacted strongly with
the westerly LLJ that provided reversed vertical wind shear below and above
the jet core. Inside mature cells, significant dynamical pressure
perturbations (<i>p'</i><sub>d</sub>) are induced with positive (negative)
<i>p'</i><sub>d</sub> at the western (eastern) flank of the updraft near the surface
and a reversed pattern aloft (> 2 km). This configuration produced an
upward-directed pressure gradient force (PGF) to the rear side and favors new
development to the west, which further leads to cell merging as the mature
cells slowdown in eastward propagation. The strong updrafts also acted to
elevate the jet and enhance the local vertical wind shear at the rear flank.
Additional analysis reveals that the upward PGF there is resulted mainly by
the shearing effect but also by the extension of upward acceleration at low
levels. In the horizontal, the upstream-directed PGF induced by the rear-side
positive <i>p'</i><sub>d</sub> near the surface is much smaller, but can provide
additional convergence for BB development upstream. Finally, the cold-pool
mechanism for BB appears to be not important in the Morakot case, as the
conditions for strong evaporation in downdrafts do not exist. |
| first_indexed | 2024-04-12T00:04:26Z |
| format | Article |
| id | doaj.art-d05bdb32404843fba812eb096f1952e7 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-12T00:04:26Z |
| publishDate | 2015-10-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-d05bdb32404843fba812eb096f1952e72022-12-22T03:56:09ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242015-10-011519110971111510.5194/acp-15-11097-2015A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maximaC.-C. Wang0H.-C. Kuo1R. H. Johnson2C.-Y. Lee3S.-Y. Huang4Y.-H. Chen5Department of Earth Sciences, National Taiwan Normal University, Taipei, TaiwanDepartment of Atmospheric Sciences, National Taiwan University, Taipei, TaiwanDepartment of Atmospheric Sciences, Colorado State University, Fort Collins, CO, USADepartment of Atmospheric Sciences, National Taiwan University, Taipei, TaiwanDepartment of Earth Sciences, National Taiwan Normal University, Taipei, TaiwanDepartment of Atmospheric Sciences, National Taiwan University, Taipei, TaiwanThis paper investigates the formation and evolution of deep convection inside the east–west oriented rainbands associated with a low-level jet (LLJ) in Typhoon Morakot (2009). With the typhoon center to the northwest of Taiwan, the westerly LLJ occurred as a result from the interaction of typhoon circulation with the southwest monsoon flow, which supplied the water vapor for the extreme rainfall (of ~ 1000 mm) over southwestern Taiwan. The Cloud-Resolving Storm Simulator with 1 km grid spacing was used to simulate the event, and it successfully reproduced the slow-moving rainbands, the embedded cells, and the dynamics of merger and back-building (BB) on 8 August as observed. Our model results suggest that the intense convection interacted strongly with the westerly LLJ that provided reversed vertical wind shear below and above the jet core. Inside mature cells, significant dynamical pressure perturbations (<i>p'</i><sub>d</sub>) are induced with positive (negative) <i>p'</i><sub>d</sub> at the western (eastern) flank of the updraft near the surface and a reversed pattern aloft (> 2 km). This configuration produced an upward-directed pressure gradient force (PGF) to the rear side and favors new development to the west, which further leads to cell merging as the mature cells slowdown in eastward propagation. The strong updrafts also acted to elevate the jet and enhance the local vertical wind shear at the rear flank. Additional analysis reveals that the upward PGF there is resulted mainly by the shearing effect but also by the extension of upward acceleration at low levels. In the horizontal, the upstream-directed PGF induced by the rear-side positive <i>p'</i><sub>d</sub> near the surface is much smaller, but can provide additional convergence for BB development upstream. Finally, the cold-pool mechanism for BB appears to be not important in the Morakot case, as the conditions for strong evaporation in downdrafts do not exist.http://www.atmos-chem-phys.net/15/11097/2015/acp-15-11097-2015.pdf |
| spellingShingle | C.-C. Wang H.-C. Kuo R. H. Johnson C.-Y. Lee S.-Y. Huang Y.-H. Chen A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima Atmospheric Chemistry and Physics |
| title | A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima |
| title_full | A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima |
| title_fullStr | A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima |
| title_full_unstemmed | A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima |
| title_short | A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima |
| title_sort | numerical study of convection in rainbands of typhoon morakot 2009 with extreme rainfall roles of pressure perturbations with low level wind maxima |
| url | http://www.atmos-chem-phys.net/15/11097/2015/acp-15-11097-2015.pdf |
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