| Cold air activity is an important weather process that affects our weather and climate,which will bring about dramatic changes of meteorological factors and have an important impact on human health and weather sensitive diseases.Especially under the background of global climate change,cold weather and climate events closely related to extreme low temperature weather events occur more frequently,bringing more significant impact on respiratory diseases such as weather-sensitive diseases.In this paper,we study the temporal and spatial distribution characteristics of cold air and the chill index in our country by means of the latest developped index.On this basis,we choose Nanjing and Lanzhou as the representatives of the north and south cities to study the effects of cold air on respiratory diseases and its mechanism.The main conclusions are as follows:(1)China’s cold air activity is characterized by mode of strong north-south and north-south distribution.The frequency of cold air was decreasing from 1961 to 2014 as a whole.By dividing the whole China into five regions,it was found that the frequency of cold air in the four areas has increased,and the frequency of the other four regions have reduced.There are obvious interdecadal variations in cold air activity.The frequency of cold air was more frequent in the 1960 s and 1970 s,significantly reduced in the 1980 s and 1990 s,and rebounded after 2000.Single cold air strength has been enhanced but not significantly,it’s duration is mainly 3-4 days.The distribution of wind chill index shows distinct characteristics of opposite distribution between the north and south.With the increasement of the wind chill from 4 to-6,the corresponding daily distribution shows the reverse phase of the north and the south,and the number of the wind chill index(-1--6)in the cold air process is the same.The 3 regions of the north were characterized as moderate cold or severe cold.Southern 2 regions areof mild cold-based.There are also some interdecadal characteristics of the time variation of the number of days of coldness,but not so obvious as cold air process.(2)The distribution of somatosensory distribution in Nanjing area in 2005-2008 was mainly dominated by heat field,and the peak of death caused by respiratory disease mainly occurred in 1,2 and 12 months each year,which was negatively correlated with the distribution of wind chill index.The correlation coefficient of monthly average number of respiratory disease deaths and the wind chill index was-0.87.The effect of meteorological factors on respiratory diseases has a significant lag effect with the correlation coefficient up to 0.63 on the third day.The thresholds of changes in meteorological factors during the cold air process with abnormal high number of respiratory diseases were: air pressure increasement was 8.6 hPa,humidity was ± 0.16,and wind chill index was-1.83.A typical cold wave process in Nanjing area was selected as a case to study,showing that the blocking high during the process were stronger,and the Siberian high pressure was significantly stronger,which resulted in a significant change in the meteorological factors.The air pressure increased by 22.1 hPa,the humidity added by 0.23,the cold index of-2.3,are more than the threshold range obtained in this paper,ultimately leading to abnormally more respiratory disease deaths.(3)A study on the effect of cold air process on respiratory diseases in Lanzhou City from 2001 to 2005 showed: the somatosentory of Lanzhou City was mainly cold days in the whole year from 2001 to 2005,and the number of patients admitted to respiratory diseases was the highest in winter.The distribution of hospitalization in cold reasons was significantly correlated with moderate number of cold days and the correlation coefficient was 0.8.Impacts of old air on the respiratory diseases are the same period,lag,early impact.Lag impact was mainly after the cold air 1-4 days,and the early impact was mainly before the cold air 1-3 days.the impact are stronger for people over 65 years of age than who was under 65 years.Respiratory system diseases in patients with unusually high meteorological factor threshold were: air pressure was 8.1hPa,the lowest temperature droppment was 3.9?C,wind chill index was-1.Choosing a cold wave process for a case analysis,it is shown that the process of Ural mountain blocking high was more west and stronger,and the ground Siberian high pressure was also more west and stronger,resulting in that cold air mainly affected northwest China.The maximum pressure droppment of 18.5hPa and the average daily temperature droppment of 12.8?C,make the number of respiratory disease hospitalization 2 times of the 5-year mean.Compared with Nanjing and Lanzhou the change of humidity has a more significant effect on Nanjing than that in Lanzhou.Lanzhou is the most significant effected by the daily minimumtemperature change,which may be due to the relatively dry drier condition in Lanzhou.The respiratory system disease is significantly related to the increase of air pressure in the two cities,while the correlation between wind chill index and the respiratory system disease is more siginificant in Nanjing than in Lanzhou.(4)Using WRF(Weather Research and Forecast)model to simulate the cold air process of Lanzhou City in April 6 to 9,2005,the simulation ability of WRF model for wind chill index was analyzed.The results show that the WRF model can simulate the situation field of the cold air process well,and can simulate the sudden changes of the meteorological factors such as temperature and air pressure during the cold air process.Therefore,the simulation can reflect the characteristics of the wind chill index and somatosensory temperature.This is a useful attempt to show that the weather model numerical simulation can provide accurate hourly meteorological elements.If the corresponding disease information could be accessed,it will be in-depth understanding of the impact of weather on human health mechanisms and related diseases and give more references to the prevention and control. |
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