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Xiaoqing Peng, Tingjun Zhang, Yijing Liu, and Jing Luo

; Devaraju et al. 2015 ; Betts et al. 2016 ). Relative to the global mean temperature, the rate and magnitude of temperature rise were much greater at high latitudes ( Symon et al. 2004 ; Screen and Simmonds 2010 ) and in high-altitude regions ( Pepin et al. 2015 ; Guo and Wang 2016 ; Wang et al. 2016 ). Permafrost regions and regions with seasonally frozen ground occupy about 24.91 × 10 6 km 2 (25.6%) and 48.12 × 10 6 km 2 (50.5%) of the exposed land surface in the Northern Hemisphere

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Gwangyong Choi, David A. Robinson, and Sinkyu Kang

1. Introduction Snowfall is a transient seasonal phenomenon over Eurasia and North America. Depending on when and where it falls, snow may remain on the ground for hours to many months. In a given location, it may accumulate and disappear several times over the course of the season. For example, this may be the case in Arctic locales during the fall, whereas it may be common throughout the winter in the middle latitudes. Northern Hemisphere continental snow extent approaches 47 × 10 6 km 2 in

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U. Ulbrich, J. G. Pinto, H. Kupfer, G. C. Leckebusch, T. Spangehl, and M. Reyers

find any apparent changes in the geographical distribution of events, as identified in a 13-member multimodel ensemble. Geng and Sugi (2003) found an increase in the number of intense cyclones, along with decreasing overall numbers for Northern Hemisphere summer and winter in a high-resolution (T106) scenario run performed with the model of the Japanese Meteorological Agency. These opposing tendencies in the total number of cyclone events versus the number of intense events were also identified

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Lizzie S. R. Froude

number of planned studies, presenting a basic analysis of the prediction of Northern Hemisphere cyclones. Further studies will perform a more in-depth regional analysis for both the Northern and Southern Hemispheres and will also attempt to understand any differences seen in the prediction of the cyclones by the different EPSs. This paper continues with a description of the data in section 2 , which is followed by a description of the analysis methodology in section 3 . In section 4 the results

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Robert X. Black and Brent A. McDaniel

frequent than SSW events, which occur at a frequency of 0.6 events per year ( Charlton and Polvani 2007 , hereafter CP ). Circumpolar (annular) variability in the Northern Hemisphere circulation provides a strong link between the winter stratospheric polar vortex and tropospheric climate ( Thompson and Wallace 2000 ; Baldwin and Dunkerton 2001 ; Thompson et al. 2005 ). In particular, the polar vortex strength is strongly connected to the Northern Hemisphere annular mode (NAM) and anomalous

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Tsing-Chang Chen

1. Introduction The Northern Hemispheric summer circulation is characterized by three monsoons: Asian, North American, and West African. In the upper troposphere, the first two monsoons are distinguished by the Tibetan and Mexican highs, which are separated by the North Pacific and North Atlantic oceanic troughs. The West African monsoon, which has a more complicated vertical structure than the other two monsoons, is reflected by the midtropospheric Saharan high, which is overlaid by the

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E. Tyrlis and B. J. Hoskins

1. Introduction A comprehensive climatology of Northern Hemisphere (NH) blocking according to the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data has been presented in Tyrlis and Hoskins (2008 , hereafter TH ). This study was based on the use of an index, B , of the meridional contrast about a central blocking latitude (CBL) of the potential temperature ( θ ) on a potential vorticity (PV) surface considered to be the dynamical tropopause, the 2-PVU

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Ross D. Brown and Philip W. Mote

and economic balance of regions far downstream by delaying the release of water months after precipitation events. Persistent changes in snow accumulation or melt can therefore have significant ecologic and economic consequences. Snow cover is also integrally linked with observed changes in global climate, especially for Northern Hemisphere (NH) land areas, through its role in modifying surface albedo. Observed monthly mean snow cover extent over the NH is strongly anticorrelated with air

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E. Tyrlis and B. J. Hoskins

blocking is sometimes related to severe droughts and heat waves (e.g., Green 1977 ; Black et al. 2004 ). The first attempt to identify the synoptic characteristics of blocking was presented by Namias (1947) in his investigation of the evolution of the Northern Hemisphere circulation anomalies during the abnormal winter of 1947/48. Berggen et al. (1949) conducted a more in-depth study of the horizontal and vertical structures of the thermal and wind fields during the European blocking event of

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Ming Cai and R-C. Ren

1. Introduction The Northern Hemisphere annular mode (NAM) is the most dominant recurrent pattern of the Northern Hemisphere (NH) atmospheric variability in winter with a time scale from a week to a few months ( Thompson and Wallace 1998 ; Baldwin and Dunkerton 1999 ). It is characterized with a ringlike seesaw oscillatory pattern between the subtropics and extratropics in both thermal and momentum fields (e.g., Thompson and Lorenz 2004 , and the references therein). The positive phase of the

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