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Caitlin C. Crossett and Nicholas D. Metz

1. Introduction Cold air is frequently advected along the lee side of high terrain and channeled equatorward, creating a cold surge. Cold surges are shallow regions of cold, stable air that extend approximately 500–1000 km, or one Rossby radius of deformation away from high terrain ( Pierrehumbert and Wyman 1985 ). Cold surges typically have a coherent signature from two days up to an entire week and are often associated with strong low-level equatorward flow exceeding 20 m s −1 , decreases in

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Jianqiong Zhan, Wenyuan Chang, Wei Li, Yanming Wang, Liqi Chen, and Jinpei Yan

humidity ( Qu et al. 2015 ; S.-H. Wang et al. 2016 ). As cold surges propagate to the south, massive amounts of northern particulates are brought to the southeastern continental edge within a shallow layer approximately 1 km above the surface ( Hsu et al. 2010 ; Yan et al. 2015 ; S.-H. Wang et al. 2016 ) and have consequently degraded air quality in the southeastern coastal region. This is different from the haze events in the NCP, where high PM 2.5 concentrations have been suggested to be mainly

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Kevin C. Prince and Clark Evans

Cordillera, cold surges that propagate through eastern Brazil occur in the absence of both an intense surface anticyclone and highly amplified upper-tropospheric longwave pattern (not shown). These situations occur in the presence of a surface cyclone off the eastern coast of South America, allowing maritime polar air to flow equatorward west of the cyclone’s center ( Lupo et al. 2001 ). Fig . 1. Topographic map of South America with the synoptic climatology of cyclone (red) and anticyclone (blue) tracks

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Jiachuan Yang and Elie Bou-Zeid

makers on the need for appropriate mitigation measures that limit summertime UHI with negligible change to the wintertime UHI. 2. Method a. Temperature data The early 2014 North American cold wave was selected as our study period. The extreme event was caused by a southward-moving cold air mass resulting from an atypical polar vortex, which reached as far south as Dallas, Texas, and set more than 49 record lows on 7 January across the United States. We collected hourly air temperature data at weather

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James S. Risbey, Didier P. Monselesan, Terence J. O’Kane, Carly R. Tozer, Michael J. Pook, and Peter T. Hayman

, 379 – 402 , . 10.1175/MWR-D-16-0291.1 Perrin , G. , and I. Simmonds , 1995 : The origin and characteristics of cold air outbreaks over Melbourne . Aust. Meteor. Mag. , 44 , 41 – 59 . Pezza , A. , and T. Ambrizzi , 2005 : Dynamical conditions and synoptic tracks associated with different types of cold surge over tropical South America . Int. J. Climatol. , 25 , 215 – 241 , . 10.1002/joc.1080 Pook , M. , J

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Thomas Haiden, C. David Whiteman, Sebastian W. Hoch, and Manuela Lehner

. 2008 ). While there was continuous cooling, a near-isothermal stratification persisted throughout the night in much of the crater atmosphere ( Fig. 1 ). A surface-based strong stability layer was present only in the lowest 20% of the crater atmosphere. This behavior was observed during several nights and represented a recurring, systematic phenomenon. On the basis of the available data, a conceptual model was proposed ( Whiteman et al. 2010 ). The conceptual model states that cold air that forms on

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Baoleerqimuge Bao and Guoyu Ren

1. Introduction Sea-effect precipitation (SEP) and lake-effect precipitation (LEP) are local or mesoscale precipitation phenomena that appear over and downwind of the sea or a lake ( Laird et al. 2009a , b ) when cold air flows over the relatively warmer water. They occur mostly in mid–high-latitude regions in late autumn and winter and are characterized by cloud streets, limited spatial distribution, short duration, and mostly snow ( Steenburgh et al. 2000 ; Yu et al. 2009 ; Laird et al

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Zhiwei Wu, Hai Lin, Yun Li, and Youmin Tang

-shifted Hawaiian high pressure system and favors cold air from the north. Fig . 4. The AM (a) climatology in SLP (contours in hectopascals), surface air temperature (Ts; color shadings in degrees Celsius), and 925-hPa winds (vectors in meters per second), and their anomalies regressed to the (b) KFF(DC) and (c) KFF(IA), as defined in Fig. 3 . Only wind speed anomalies above 1 m s −1 are plotted. For a high KFF(IA) year ( Fig. 4c ), the surface circulation pattern is similar to that of a high KFF(DC), except

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Chenjie Huang, Y-L. Lin, M. L. Kaplan, and J. J. Charney

-tropospheric northeasterly winds at the northeast periphery of a high pressure ridge that was just off the western U.S. coast advected the dry air southwestward toward the California coast; 3) the increasing curvature of the upper-level jet-front system and the strong cold-air advection over the southwestern United States strengthened the meso- α -scale subsidence; 4) the first dry-air surge within the PBL in southern California before 0000 UTC 26 October was caused by moisture divergence associated with the surface

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José A. Marengo, Carlos A. Nobre, and Alistair D. Culf

Introduction Surges of cold polar air that move across southeastern Brazil and the Amazon region from the south, greatly modifying the atmospheric structure and climatic conditions, are known locally as friagens (friagem in singular). These events can produce severe frosts in the coffee growing areas of southern Brazil and substantial cooling in the Amazon basin. The cold front heading these thrusts of polar air may reach as far north as the equator. The events are relatively common in the

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