Identification

Title

Distant effects of a recurving tropical cyclone on rainfall in a midlatitude convective system: A high-impact predecessor rain event

Abstract

Recent research has identified predecessor rain events (PREs), which are mesoscale regions of heavy rainfall that occur 1000 km poleward and downshear of recurving tropical cyclones (TCs). PREs typically occur 24 - 36 h prior to the arrival of the main rain shield associated with the TC, and frequently result in damaging flooding. A distinguishing feature of a PRE is that it is enhanced by a broad region of deep tropical moisture directly associated with the TC that is transported well poleward ahead of the TC. This study will quantify the effects of the tropical moisture from one TC on a record-breaking rain and flood event over the northern Great Plains and southern Great Lakes region on 18 - 19 August 2007. In this event, which occurred ahead of TC Erin, a southerly stream of deep tropical moisture (precipitable water values >50 mm) moved poleward and intersected a northwest - southeast-oriented quasi-stationary baroclinic zone beneath the equatorward entrance region of an upper-level jet streak. A slow-moving mesoscale convective system (MCS) developed and produced widespread heavy rainfall, with local amounts exceeding 380 mm that resulted in historic flooding in Minnesota and Wisconsin. Observations and numerical simulations using the Advanced Research Weather Research and Forecasting model (ARW-WRF) indicate that low-level frontogenesis was maximized during the overnight hours of 19 August 2007 and provided the forcing for vigorous ascent during the mature stage of the PRE. A control simulation, which included the poleward transport of TC Erin-related moisture, reproduced the extreme rainfall amounts, although the simulated rainfall was displaced from where it was observed. A sensitivity simulation in which the moisture associated with TC Erin was removed (referred to as "NOPLUME") shows reduced convective available potential energy (CAPE) in the inflow region of the PRE and a less vigorous MCS. In all, there was an approximately 50% reduction in the maximum precipitation amount and a 25% reduction in the total precipitation from the control simulation to the NOPLUME run. Or, considered in the context of rainfall enhancement by the Erin-related moisture, there was a near doubling of the maximum amount and a 33% increase in the total rainfall. The extent of these differences underscores the importance of moisture originating from TC Erin in transforming a heavy rain event into a high-impact, record-breaking rain event.

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document

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http://n2t.net/ark:/85065/d7r211xj

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eng

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geoscientificInformation

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publication

effective date

2016-01-01T00:00:00Z

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publication

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2011-02-01T00:00:00Z

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Copyright 2011 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be "fair use" under Section 107 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Law (17 USC, as revised by P.L. 94-553) does not require the Society's permission. Republication, systematic reproduction, posting in electronic form on servers, or other uses of this material, except as exempted by the above statements, requires written permission or license from the AMS. Additional details are provided in the AMS Copyright Policies, available from the AMS at 617-227-2425 or amspubs@ametsoc.org. Permission to place a copy of this work on this server has been provided by the AMS. The AMS does not guarantee that the copy provided here is an accurate copy of the published work.

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OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

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