Case Study of the Leeside Mesolow and Mesocyclone in TAMEX

Chung-Chieh Wang Department of Environmental Management, Jin-Wen Institute of Technology, Taipei, Taiwan, Republic of China

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George Tai-Jen Chen Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan, Republic of China

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Abstract

An observational study was performed on a leeside mesolow case that occurred 8 June 1987 during the Taiwan Area Mesoscale Experiment (TAMEX). The case developed as prevailing west-southwest winds strengthened and interacted with the terrain of Taiwan, with a Froude number (Fr = U/Nh) increasing from below 0.3 to over 0.5. A quasi-stationary mesolow formed to the southeast of Taiwan with no closed circulation through most of its 13-h life stages until passage of the Mei-yu front. A stationary and localized mesovortex also formed about 90 km southwest of the low center, but little adjustment was observed between the mesolow and the vortex.

Results suggest that airflow at lower levels was blocked and moved around the terrain of the southern Central Mountain Range (CMR). This led to the formation of low-level jets (LLJs) both to the northwest and southeast of Taiwan. The latter branch provided shear vorticity in the background region of the vortex. Air parcels at higher levels, on the other hand, tended to climb over the mountain and caused precipitation on the windward slope, then subsided at the lee side. The subsidence produced the mesolow through adiabatic warming and drying, which was strongest between 1 and 2 km. Latent heat release at the windward side was estimated to contribute a maximum of about 55%–60% of the total warming. Eventually, as the Mei-yu front moved southward along the eastern coast of Taiwan, the mesolow merged with the front and transformed into a migratory mesocyclone along the front.

Corresponding author address: Dr. George Tai-Jen Chen, Department of Atmospheric Sciences, National Taiwan University, 61, Ln. 144, Sec. 4, Keelung Rd., Taipei 10772, Taiwan. Email: george@george2.as.ntu.edu.tw

Abstract

An observational study was performed on a leeside mesolow case that occurred 8 June 1987 during the Taiwan Area Mesoscale Experiment (TAMEX). The case developed as prevailing west-southwest winds strengthened and interacted with the terrain of Taiwan, with a Froude number (Fr = U/Nh) increasing from below 0.3 to over 0.5. A quasi-stationary mesolow formed to the southeast of Taiwan with no closed circulation through most of its 13-h life stages until passage of the Mei-yu front. A stationary and localized mesovortex also formed about 90 km southwest of the low center, but little adjustment was observed between the mesolow and the vortex.

Results suggest that airflow at lower levels was blocked and moved around the terrain of the southern Central Mountain Range (CMR). This led to the formation of low-level jets (LLJs) both to the northwest and southeast of Taiwan. The latter branch provided shear vorticity in the background region of the vortex. Air parcels at higher levels, on the other hand, tended to climb over the mountain and caused precipitation on the windward slope, then subsided at the lee side. The subsidence produced the mesolow through adiabatic warming and drying, which was strongest between 1 and 2 km. Latent heat release at the windward side was estimated to contribute a maximum of about 55%–60% of the total warming. Eventually, as the Mei-yu front moved southward along the eastern coast of Taiwan, the mesolow merged with the front and transformed into a migratory mesocyclone along the front.

Corresponding author address: Dr. George Tai-Jen Chen, Department of Atmospheric Sciences, National Taiwan University, 61, Ln. 144, Sec. 4, Keelung Rd., Taipei 10772, Taiwan. Email: george@george2.as.ntu.edu.tw

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  • Baines, P. G., 1995: Topographic effects in stratified flows. Cambridge University Press, 482 pp.

  • Bell, G. D., and L. F. Bosart, 1988: Appalachian cold-air damming. Mon. Wea. Rev., 116 , 137161.

  • Bougeault, P., and Coauthors. 2001: The MAP Special Observing Period. Bull. Amer. Meteor. Soc., 82 , 433462.

  • Chen, G. T. J., 1991: Observational study on mesoscale features in Taiwan Mei-Yu season (I). Research Rep. NTUATM-1991-001, (in Chinese with English abstract). Department of Atmospheric Sciences, National Taiwan University, 136 pp.

    • Search Google Scholar
    • Export Citation
  • Chen, G. T. J., . 1992a: Mesoscale features observed in Taiwan Mei-Yu season. J. Meteor. Soc. Japan, 70 , 497516.

  • Chen, G. T. J., . 1992b: Observational study on mesoscale features in Taiwan Mei-Yu season (II). Research Rep. NTUATM-1992-001, (in Chinese with English abstract). Department of Atmospheric Sciences, National Taiwan University, 185 pp.

    • Search Google Scholar
    • Export Citation
  • Crook, N. A., T. L. Clark, and M. W. Moncrieff, 1990: The Denver Cyclone. Part I: Generation in low Froude number flow. J. Atmos. Sci., 47 , 27252742.

    • Search Google Scholar
    • Export Citation
  • Davis, C. A., 1997: Mesoscale anticyclone circulations in the lee of the central Rocky Mountains. Mon. Wea. Rev., 125 , 28382855.

  • Ferber, G. K., and C. F. Mass, 1990: Surface pressure perturbations produced by an isolated mesoscale topographic barrier. Part II: Influence on regional circulations. Mon. Wea. Rev., 118 , 25972606.

    • Search Google Scholar
    • Export Citation
  • Forbes, G. S., R. A. Anthes, and D. W. Thompson, 1987: Synoptic and mesoscale aspects of an Appalachian ice storm associated with cold-air damming. Mon. Wea. Rev., 115 , 564591.

    • Search Google Scholar
    • Export Citation
  • Georgelin, M., E. Richard, and M. Petididier, 1996: The impact of diurnal cycle on a low-Froude number flow observed during the PYREX Experiment. Mon. Wea. Rev., 124 , 11191131.

    • Search Google Scholar
    • Export Citation
  • Holton, J. R., 1992: An Introduction to Dynamic Meteorology. 3d ed. Academic Press, 511 pp.

  • Hunt, J. C. R., and W. H. Snyder, 1980: Experiments on stably and neutrally stratified flow of a model three-dimensional hill. J. Fluid Mech., 96 , 671704.

    • Search Google Scholar
    • Export Citation
  • Kuo, Y-H., and G. T. J. Chen, 1990: Taiwan Area Mesoscale Experiment. An Overview. Bull. Amer. Meteor. Soc., 71 , 488503.

  • Lee, T-Y., Y-Y. Park, and Y-L. Lin, 1998: A numerical modeling study of mesoscale cyclogenesis to the east of the Korean peninsula. Mon. Wea. Rev., 126 , 23052329.

    • Search Google Scholar
    • Export Citation
  • Li, J., and Y-L. Chen, 1998: Barrier jets during TAMEX. Mon. Wea. Rev., 126 , 959971.

  • Lin, Y-L., N-H. Lin, and R. P. Weglarz, 1992: Numerical modeling studies of lee mesolows, mesovortices and mesocyclones with application to the formation of Taiwan mesolows. Meteor. Atmos. Phys., 49 , 4367.

    • Search Google Scholar
    • Export Citation
  • Manins, P. C., and B. L. Sawford, 1982: Mesoscale observations of upstream blocking. Quart. J. Roy. Meteor. Soc., 108 , 427434.

  • Peng, M. S., S-W. Li, S. W. Chang, and R. T. Williams, 1995: Flow over mountains: Coriolis force, transient troughs and three dimensionality. Quart. J. Roy. Meteor. Soc., 121 , 593613.

    • Search Google Scholar
    • Export Citation
  • Reisner, J. M., and P. K. Smolarkiewicz, 1994: Thermally forced low Froude number flow past three-dimensional obstacles. J. Atmos. Sci., 51 , 117133.

    • Search Google Scholar
    • Export Citation
  • Rotunno, R., V. Grubisic, and P. K. Smolarkiewicz, 1999: Vorticity and potential vorticity in mountain wakes. J. Atmos. Sci., 56 , 27962810.

    • Search Google Scholar
    • Export Citation
  • Schär, C., and R. B. Smith, 1993: Shallow-water flow past isolated topography. Part I: Vorticity production and wake formation. J. Atmos. Sci., 50 , 13731400.

    • Search Google Scholar
    • Export Citation
  • Sheppard, P. A., 1956: Airflow over mountains. Quart. J. Roy. Meteor. Soc., 82 , 528529.

  • Smith, R. B., 1980: Linear theory of stratified hydrostatic flow past an isolated mountain. Tellus, 32 , 348364.

  • Smith, R. B., . 1982: Synoptic observations and theory of orographically disturbed wind and pressure. J. Atmos. Sci., 39 , 6070.

  • Smith, R. B., . 1989: Hydrostatic airflow over mountains. Advances in Geophysics, Vol. 31, Academic Press, 1–41.

  • Smith, R. B., . 1990: Why can't stably stratified air rise over high ground? Atmospheric Processes over Complex Terrain, W. Blumen, Ed., Meteor. Monogr., No. 23, Amer. Meteor. Soc., 105–107.

    • Search Google Scholar
    • Export Citation
  • Smith, R. B., and V. Grubišić, 1993: Aerial observations of Hawaii's wake. J. Atmos. Sci., 50 , 37283750.

  • Smolarkiewicz, P. K., and R. Rotunno, 1989: Low Froude number flow past three-dimensional obstacles. Part I: Baroclinically generated lee vortices. J. Atmos. Sci., 46 , 11541164.

    • Search Google Scholar
    • Export Citation
  • Smolarkiewicz, P. K., R. Rasmussen, and T. L. Clark, 1988: On the dynamics of Hawaiian cloud band: Island forcing. J. Atmos. Sci., 45 , 18721905.

    • Search Google Scholar
    • Export Citation
  • Sun, W-Y., and J-D. Chern, 1993: Diurnal variation of lee vortices in Taiwan and the surrounding area. J. Atmos. Sci., 50 , 34043430.

  • Wang, S. T., 1990: Subjective mesoscale analysis data during Taiwan Area Mesoscale Experiment (TAMEX). Vol. 1, Original Surface Map Collection during TAMEX Intensive Observing Periods (IOPs), Central Weather Bureau of ROC, 479 pp. [Available from the Dept. of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan, ROC.].

    • Search Google Scholar
    • Export Citation
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