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    High-Resolution Observations of the Trowal–Warm-Frontal Region of Two Continental Winter Cyclones

    Source: Monthly Weather Review:;2007:;volume( 135 ):;issue: 005::page 1629
    Author:
    Grim, Joseph A.
    ,
    Rauber, Robert M.
    ,
    Ramamurthy, Mohan K.
    ,
    Jewett, Brian F.
    ,
    Han, Mei
    DOI: 10.1175/MWR3378.1
    Publisher: American Meteorological Society
    Abstract: This paper compares the structure of the trough of warm air aloft (trowal)?warm-frontal region of two continental wintertime cyclones. The cyclones were observed over the central Great Lakes region during the Lake-Induced Convection Experiment/Snowband Dynamics Project field campaign. The cyclones had different origins, with the first forming east of the Colorado Rockies and the second forming over the Gulf of Mexico. They were associated with different upper-level flow regimes, one located just north of a nearly zonal jet and the other located just west of a nearly meridional jet. Both storms produced heavy swaths of snow across the states of Illinois, Wisconsin, and Michigan. High-resolution observations of frontal structure were made during flights of the National Center for Atmospheric Research Electra aircraft using dropsondes and the Electra Doppler Radar tail radar system. The high-resolution observations suggest a different arrangement of air masses in the trowal region compared with the classical occlusion model, where the trowal axis forms at the intersection of a warm front and a cold front that has overtaken and subsequently ascended the warm front. In both cyclones dry air intruded over the warm front, isolating the warm, moist airflow within the trowal airstream. Very sharp moisture gradients were present at the leading edge of the dry air in both cyclones. In each case, relative humidity differences of over 50% were observed over distances of 10?20 km. The thermal gradient near the leading edge of the dry air in one cyclone was diffuse, so that the moist?dry boundary could best be characterized as an upper-level humidity front. In the other cyclone, the thermal gradient was sharper and aligned with the moisture boundary and was best characterized as a cold front aloft. The analyses suggest that the classical conceptual model of the trowal, at least in some cyclones such as the two illustrated here, needs to be revised to include the possibility that the warm moist airstream aloft may sometimes be bounded on its south side by an upper-level front rather than a surface-based cold front. Since the two cyclones discussed here had different origins, tracks, and flow regimes, the similarity of their structure suggests that these features may be common.
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      High-Resolution Observations of the Trowal–Warm-Frontal Region of Two Continental Winter Cyclones

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    http://yetl.yabesh.ir/yetl1/handle/yetl/4229425
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    contributor authorGrim, Joseph A.
    contributor authorRauber, Robert M.
    contributor authorRamamurthy, Mohan K.
    contributor authorJewett, Brian F.
    contributor authorHan, Mei
    date accessioned2017-06-09T17:28:28Z
    date available2017-06-09T17:28:28Z
    date copyright2007/05/01
    date issued2007
    identifier issn0027-0644
    identifier otherams-85924.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4229425
    description abstractThis paper compares the structure of the trough of warm air aloft (trowal)?warm-frontal region of two continental wintertime cyclones. The cyclones were observed over the central Great Lakes region during the Lake-Induced Convection Experiment/Snowband Dynamics Project field campaign. The cyclones had different origins, with the first forming east of the Colorado Rockies and the second forming over the Gulf of Mexico. They were associated with different upper-level flow regimes, one located just north of a nearly zonal jet and the other located just west of a nearly meridional jet. Both storms produced heavy swaths of snow across the states of Illinois, Wisconsin, and Michigan. High-resolution observations of frontal structure were made during flights of the National Center for Atmospheric Research Electra aircraft using dropsondes and the Electra Doppler Radar tail radar system. The high-resolution observations suggest a different arrangement of air masses in the trowal region compared with the classical occlusion model, where the trowal axis forms at the intersection of a warm front and a cold front that has overtaken and subsequently ascended the warm front. In both cyclones dry air intruded over the warm front, isolating the warm, moist airflow within the trowal airstream. Very sharp moisture gradients were present at the leading edge of the dry air in both cyclones. In each case, relative humidity differences of over 50% were observed over distances of 10?20 km. The thermal gradient near the leading edge of the dry air in one cyclone was diffuse, so that the moist?dry boundary could best be characterized as an upper-level humidity front. In the other cyclone, the thermal gradient was sharper and aligned with the moisture boundary and was best characterized as a cold front aloft. The analyses suggest that the classical conceptual model of the trowal, at least in some cyclones such as the two illustrated here, needs to be revised to include the possibility that the warm moist airstream aloft may sometimes be bounded on its south side by an upper-level front rather than a surface-based cold front. Since the two cyclones discussed here had different origins, tracks, and flow regimes, the similarity of their structure suggests that these features may be common.
    publisherAmerican Meteorological Society
    titleHigh-Resolution Observations of the Trowal–Warm-Frontal Region of Two Continental Winter Cyclones
    typeJournal Paper
    journal volume135
    journal issue5
    journal titleMonthly Weather Review
    identifier doi10.1175/MWR3378.1
    journal fristpage1629
    journal lastpage1646
    treeMonthly Weather Review:;2007:;volume( 135 ):;issue: 005
    contenttypeFulltext
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