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Using the Weather Research and Forecasting model, numerical experiments with reconstructed ideal zonally uniform sea surface temperatures were designed to discuss the midlatitude upper‐level zonal wind response to the change of subtropical front strength over the North Pacific in winter. The results show that the enhancement of the subtropical frontal zone (STFZ) of the North Pacific leads to the stronger upper zonal wind, without considering the lateral boundary barotropic and baroclinic disturbances in this regional model. The enhanced STFZ first results in positive meridional temperature gradient anomalies by affecting the sea surface sensible heat flux. Then the low‐level wind increases because of the increased thermal wind. In addition, the temperature gradient anomalies spread to middle and upper troposphere by baroclinic waves, causing the increase of Eady growth rate and enhanced storm tracks on the southern side of the STFZ and the decrease on the northern side. The strengthened storm tracks give rise to a stronger midlatitude westerly jet accompanied with a southward movement through wave‐mean flow interaction, including both barotropical energy conversion and the Rossby wave breaking.

Different hepatitis C virus (HCV) genotypes exhibit differences in disease pathogenesis and progression, as well as disease outcomes and response to therapy. Tracking the change of HCV genotypes in various epidemiological settings is critical for both disease surveillance and the development of improved antiviral treatment. Here, we tracked the changes in the prevalence of the HCV genotypes in China between 2004-2007 and 2008-2011. HCV-RNA-positive sera were collected from volunteer blood donors during the period 2008-2011. The genotypes were determined by phylogenic analysis using the NS5B and E1 sequences. Geographical and demographic distribution patterns related to the HCV genotypes obtained in 2008-2011 were compared with our previous study, which recorded data in the period 2004-2007. Pearson chi-square test and t-test were used to statistically analyze the results. In 2008-2011, HCV subtypes 1b and 6a were detected in 43.8 % (184/420) and 34.3 % (144/420), respectively. The male/female ratio was found to be higher for HCV genotype 6 than for genotypes 1 and 2. When compared with the period of 2004-2007, although no significant difference was found in gender or age for genotypes 1, 2, 3 and 6, the subtype 6a frequency was significantly increased from 11 % to 26.5 % in the blood donors from outside of Guangdong Province in 2008-2011. A pattern of increase in HCV subtype 6a was found in blood donors outside of Guangdong Province, indicating that HCV subtype 6a has rapidly spread from Guangdong to other regions of China over the past 10 years.Electronic supplementary materialThe online version of this article (doi:10.1007/s00705-014-2185-1) contains supplementary material, which is available to authorized users.