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1.
In order to clarify the statistical pattern by which landfalling strong tropical cyclones(LSTCs)influenced the catastrophic migrations of rice brown planthopper(BPH),Nilaparvata lugens(stl)in China,the data of the LSTCs in China and the lighting catches of BPH that covered the main Chinese rice-growing regions from 1979 to 2008 were collected and analyzed in this work with the assistance of ArcGIS9.3,a software of geographic information system.The results were as follows:(1)In China,there were 220 strong tropical cyclones that passed the main rice-growing regions and 466 great events of BPH’s immigration in the 30 years from 1979 to 2008.73 of them resulted in the occurrence of BPH’s catastrphic migration(CM)events directly and 147 of them produced indirect effect on the migrations.(2)The number of the LSTCs was variable in different years during 1979 to 2008 and their influence was not the same in the BPH’s northward and southward migrations in the years.In the 30 years,the LSTCs brought more obvious influence on the migrations in 1980,1981,2005,2006 and 2007.The influence was the most obvious in2007 and all of the 7 LSTCs produced remarkable impact on the CMs of BPH’s populations.The effect of the LSTCs on the northward immigration of BPH’s populations was the most serious in 2006 and the influence on the southward immigration was the most remarkable in 2005.(3)In these years,the most of LSTCs occurred in July,August and September and great events of BPH's immigration occurred most frequently in the same months.The LSTCs played a more important role on the CM of BPH’s populations in the three months than in other months.(4)The analysis on the spatial distribution of the LSTCs and BPH’s immigration events for the different provinces showed that the BPH’s migrations in the main rice-growing regions of the Southeastern China were influenced by the LSTCs and the impact was different with the change of their spatial probability distribution during their passages.The most serious influence of the LSTCs on the BPH’s migrations occurred in Guangdong and Fujian provinces.(5)The statistical results indicated that a suitable insect source is an indispensable condition of the CMs of BPH when a LSTC influenced a rice-growing region.  相似文献   

2.
With the aim to examine variations in the migration phenology and population of N. lugens along with the advance/retreat of the Asian summer monsoon(ASM) and lay the foundation for further study on predicting the timing and location of N. lugens outbreak, correlation analysis and spatial analysis were applied for estimating the impact of the ASM and its related meteorological factors on the migration phenology and population of N. lugens in China in this paper. The ASM had a positive effect on the occurrence and outbreak of N. lugens. First, the first appearance date of N.lugens was consistent with seasonal advances of the northernmost location of the ASM, and the ASM provided the dynamic condition for the northward migration of N. lugens. Second, outbreak of N. lugens occurred in the area under the control of the ASM, and the ASM provided the survival condition for the population of N. lugens. Third, the population was positively related to the northernmost location of the ASM, θ_E(850 hPa) and wind speed(850 hPa).Particularly, the stronger southwest wind caused the date of the first, peak and last catches of N. lugens to turn up earlier than in the extremely years.  相似文献   

3.
IAP-GCM is used to document the forced teleresponse of the atmosphere to anomalies of the Antarctic sea ice as the important triggering mechanism for intraseasonal atmospheric oscillations across the globe. The time series of pentad-averaged deviations are then focused on and. with the band-pass filter approach, to address essential features of the 30-60 day low-frequency oscillation in the response field. It is found that tile atmospheric response to the retreat of the Antarctic sea ice is of low frequency at a period of 30-60 days. The main component is the 30-60 day intraseasonal oscillation in the forced field, with the vertical structure and distribution features similar to real atmosphere.  相似文献   

4.
Based on the number of foggy days in Nanjing in December from 1980 to 2011, we analyzed the surface temperature and atmospheric circulation characteristics of foggy years and less-foggy years. Positive anomalies of the Arctic Oscillation (AO) were found to weaken the East Asian trough, which is not conducive to the southward migration of cold air. Simultaneously, this atmospheric condition favors stability as a result of a high-pressure anomaly from the middle Yangtze River Delta region. A portion of La Ni?a events increases the amount of water vapor in the South China Sea region, so this phenomenon could provide the water vapor condition required for foggy days in Nanjing. Based on the data in December 2007, which contained the greatest number of foggy days for the years studied, the source of fog vapor in Nanjing was primarily from southern China and southwest Taiwan Island based on a synoptic scale study. The water vapor in southern China and in the southwestern flow increased, and after a period of 2-3 days, the humidity in Nanjing increased. Simultaneously, the water vapor from the southwestern of Taiwan Island was directly transported to Nanjing by the southerly wind. Therefore, these two areas are the most important sources of water vapor that results in heavy fog in Nanjing. Using the bivariate Empirical Orthogonal Function (EOF) mode on the surface temperature and precipitable water vapor, the first mode was found to reflect the seasonal variation from early winter to late winter, which reduced the surface temperature on a large scale. The second mode was found to reflect a large-scale, northward, warm and humid airflow that was accompanied by the enhancement of the subtropical high, particularly between December 15-21, which is primarily responsible for the consecutive foggy days in Nanjing.  相似文献   

5.
There has been a lot of discussion about the atmospheric heat source over the Tibetan Plateau （TP） and the low-frequency oscillation of atmospheric circulation. However, the research on low-frequency oscillation of heat source over TP and its impact on atmospheric circulation are not fully carried out. By using the vertically integrated apparent heat source which is calculated by the derivation method, main oscillation periods and propagation features of the summer apparent heat source over the eastern TP （Q1ETP） are diagnosed and analyzed from 1981 to 2000. The results are as follows： （1） Summer Q1ETP has two significant oscillation periods： one is 10-20d （BWO, Quasi-Biweekly Oscillation） and the other is 30-60d （LFO, Low-frequency Oscillation）. （2） A significant correlation is found between Q1ETP and rainfall over the eastern TP in 1985 and 1992, showing that the low-frequency oscillation of heat source is likely to be stimulated by oscillation of latent heat. （3） The oscillation of heat source on the plateau mainly generates locally but sometimes originates from elsewhere. The BWO of Q1ETP mainly exhibits stationary wave, sometimes moves out （mainly eastward）, and has a close relationship with the BWO from the Bay of Bengal. Showing the same characteristics as BWO, the LFO mainly shows local oscillation, occasionally propagates （mainly westward）, and connects with the LFO from East China. In summary, more attention should be paid to the study on BWO of Q1ETP.  相似文献   

6.
Variation in length of day of the Earth (LOD, equivalent to the Earth’s rotation rate) versus change in atmospheric geopotential height fields and astronomical parameters were analyzed for the years 1962-2006. This revealed that there is a 27.3-day and an average 13.6-day periodic oscillation in LOD and atmospheric pressure fields following lunar revolution around the Earth. Accompanying the alternating change in celestial gravitation forcing on the Earth and its atmosphere, the Earth’s LOD changes from minimum to maximum, then to minimum, and the atmospheric geopotential height fields in the tropics oscillate from low to high, then to low. The 27.3-day and average 13.6-day periodic atmospheric oscillation in the tropics is proposed to be a type of strong atmospheric tide, excited by celestial gravitation forcing. A formula for a Tidal Index was derived to estimate the strength of the celestial gravitation forcing, and a high degree of correlation was found between the Tidal Index determined by astronomical parameters, LOD, and atmospheric geopotential height. The reason for the atmospheric tide is periodic departure of the lunar orbit from the celestial equator during lunar revolution around the Earth. The alternating asymmetric change in celestial gravitation forcing on the Earth and its atmosphere produces a "modulation" to the change in the Earth’s LOD and atmospheric pressure fields.  相似文献   

7.
The onset of the Asian summer monsoon has been a focus in the monsoon study for many years. In this paper, we study the variability and predictability of the Asian summer monsoon onset and demonstrate that this onset is associated with specific atmospheric circulation characteristics. The outbreak of the Asian summer monsoon is found to occur first over the southwestern part of the South China Sea (SCS) and the Malay Peninsula region, and the monsoon onset is closely related to intra-seasonal oscillations in the lower atmosphere. These intra-seasonal oscillations consist of two low-frequency vortex pairs, one located to the east of the Philippines and the other over the tropical eastern Indian Ocean. Prior to the Asian summer monsoon onset, a strong low-frequency westerly emerges over the equatorial Indian Ocean and the low-frequency vortex pair develops symmetrically along the equator. The formation and evolution of these low-frequency vortices are important and serve as a good indicator for the Asian summer monsoon onset. The relationship between the northward jumps of the westerly jet over East Asia and the Asian summer monsoon onset over SCS is investigated. It is shown that the northward jump of the westerly jet occurs twice during the transition from winter to summer and these jumps are closely related to the summer monsoon development. The first northward jump (from 25–28N to around 30N) occurs on 8 May on average, about 7 days ahead of the summer monsoon onset over the SCS. It is found that the reverse of meridional temperature gradient in the upper-middle troposphere (500–200 hPa) and the enhancement and northward movement of the subtropical jet in the Southern Hemispheric subtropics are responsible for the first northward jump of the westerly jet.  相似文献   

8.
Based on the NCEP/NCAR reanalysis data and the observed precipitation data in the south of China from 1958 to 2000,the impact of 30 to 60 day oscillation of atmospheric heat sources on the drought and flood events in June in the south of China is discussed.During the flood(drought) events,there exists an anomalous low-frequency anticyclone(cyclone) at the low level of the troposphere over the South China Sea and the northwestern Pacific,accompanied with anomalous low-frequency heat sinks(heat sources),while there exists an anomalous low-frequency cyclone(anticyclone) with anomalous heat sources(sinks) over the area from the south of China to the south of Japan.On average,the phase evolution of the low-frequency in drought events is 7 to 11 days ahead of that in flood events in May to June in the south of China.In flood events,low-frequency heat sources and cyclones are propagated northward from the southern South China Sea,northwestward from the warm pool of the western Pacific and westward from the northwestern Pacific around 140°E,which have very important impact on the abundant rainfall in June in the south of China.However,in drought events,the northward propagations of the low-frequency heat sources and cyclones from the South China Sea and its vicinity are rather late compared with those in flood events,and there is no obvious westward propagation of the heat sources from the northwestern Pacific.The timing of the low-frequency heat source propagation has remarkable impact on the June rainfall in the south of China.  相似文献   

9.
By using the upper-wind data from July 1980 to June 1983,the variations of the low-frequency oscillation(LFO)in the atmosphere before and during 1982 El Nino have been investigated.Before the El Nino,the LFOpropagates from west to east over the equator of the Eastern Hemisphere and from east to west over 20°N.The eastward propagating LFO over the equator consists of zonal wavenumber 1 propagating eastward andzonal wavenumber 2 with a character of stationary wave.The oscillation of zonal wavenumber 2 can modulatethe oscillation strength.After the onset of the El Nino,the propagating directions of the LFO over the equatorand 20°N of the Eastern Hemisphere change to be westward and eastward,respectively.The LFO over thewestern Pacific weakens rapidly and one coming from middle and high latitudes propagates to the equator.From the phase compositions of streamline fields for the zonal wavenumber 1 of equatorial westward propa-gatirg LFO,it is found that the atmospheric heat source in the equator of the eastern Pacific(EEP)excites aseries of the equatorial cyclones and anticyclones which move northward and westward and form the westwardpropagating LFO over the equator.With the wavelength of 20000km,this kind of equatorial wave is similarto the mixing Rossby-gravity wave.In its westward and northward movement,the circulation in East Asiais modified.This may be the mechanism of the influence of El Nino on the climate of China.  相似文献   

10.
Based on daily NCEP reanalysis data, OLR and satellite rainfall data, the characteristic of the activities of South China Sea summer monsoon(SCSSM) in 2004 were analyzed. The results showed that the establishment of SCSSM was little later than normal and the intensity was stronger than normal. Influenced by the location of the northwest Pacific subtropical high, which was much northward and westward than normal, SCSSM was active mainly in the South China Sea areas. There existed obvious intraseasonal oscillation and two significant periods of SCSSM, one was about 20-30 days and the other about 40-50 days. The transportation of moisture was concentrated on the South China Sea and the northwest Pacific regions, reducing the northward transportation and resulting in drought in southern China  相似文献   

11.
The variations noticed in the atmospheric electric field recorded at Pune (18o32’N, 73o51’E, 559 m ASL), a tropi-cal inland station located in Deccan Plateau, India, during the period 1930-1987, have been examined in relation to the variations observed in the Angstrom turbidity coefficient (β) and selected meteorological parameters. The month-ly and annual mean values of the atmospheric electric field, Angstrom turbidity coefficient (β), rainfall, temperature and relative humidity for the years 1930-1938, 1957-1958, 1964-1965, 1973-1974 and 1987 were considered in the study.The results of the above study indicated gradual increases in the atmospheric electric field over the period of study (1930-1987) which is statistically significant at less than 5% level. The increases noticed during different periods varied from 30 to 109 %. The increase noticed during the period (1930-1938) and (1973-1974) was maximum (109%). The Angstrom turbidity coefficient also showed systematic increases during the period of study, which is consistent. The diurnal curve of the atmospheric electric field at the station by and large, showed a double oscillation, which is generally observed in the continental environments.  相似文献   

12.
A barotropic channel model in β-plane is used to study the effect of topographic forcing on the formation and maintenance of blocking. The approximate analytical solution of potential vorticity equation can show the main property of the whole process of blocking. It is indicated that the topographic forcing is one of the main factors caus-ing the blocking process. The results suggest that the nonlinear interaction plays a very important role in the stable “Ω” situation of blocking. The atmospheric circulation with periodic and low-frequency oscillation, perhaps, is partly caused by topographic forcing.  相似文献   

13.
Meteorological conditions, particularly the vertical wind field structure, have a direct influence on the PM2.5 concentrations over the Pearl River Delta (PRD). In October 2012, an exceptional air pollution event occurred in the PRD, and a high concentration of PM2.5 was registered at some stations. During days with PM2.5 air pollution, the wind speed was less than 3 m s-1 at the surface, and the vertical wind field featured a weak wind layer (WWL) with a thickness of approximately 1000 m. The mean atmospheric boundary layer height was less than 500 m during pollution days, but it was greater than 1400 m during non-pollution days. A strong negative correlation was detected between the PM2.5 concentration and the ventilation index (VI). The VI was less than 2000 m2 s?1 during PM2.5 air pollution days. Because of the weak wind, sea–land breezes occurred frequently, the recirculation factor (RF) values were small at a height of 800 m during pollution days, and the zones with the lowest RF values always occurred between the heights of 300 and 600 m. The RF values during PM2.5 pollution days were approximately 0.4 to 0.6 below a height of 800 m, reducing the transportation capacity of the wind field to only 40% to 60%. The RF and wind profile characteristics indicated that sea–land breezes were highly important in the accumulation of PM2.5 air pollution in the PRD. The sea breezes may transport pollutants back inland and may result in the peak PM2.5 concentrations at night.  相似文献   

14.
This study investigates the relationship between summer low-frequency rainfall over southern China and tropical intraseasonal oscillation (ISO) in the atmosphere by examining systematically the propagation features of the tropical ISO in terms of focusing on five large-scale low-frequency rainfall regimes in summer over southern China. It is demonstrated that there is a close linkage between the five rainfall regimes over southern China and the northward propagation of the tropical ISO. The moist ISO signals, which influence the low-frequency rainfall events in different regions of southern China, mainly propagate northwestward from the tropical ocean to the southeast of China. The southeast China rainfall regime is intimately associated with the moist ISO signals propagating northwestward from the equatorial mid-western Pacific Ocean. For both the Yangtze River regime and South of Yangtze River regime, the moist ISO signals over the northern South China Sea show an evident northward propagation towards the Yangtze River region, and then propagate westward. It is further found that the interaction between the northward propagation of low-latitude ISO signals and the southward propagation of high-latitude ISO signals can also make a clear influence on the low-frequency rainfall in southern China. For the Southern China regime, the moist ISO signals show a significant northward propagation from the Philippines. Moreover, for the rainless regime, southern China is under dry ISO signals’ control, and the latter shows no clear propagation to southern China. This study may provide insights for the extended-range forecasting of summer rainfall in southern China.  相似文献   

15.
Daily 850-hPa meridional wind fields in East Asia from March to September 2002 were used to establish a model of the principal oscillation pattern (POP). This model was then used to conduct independent extended-range forecasts of the principal temporal and spatial variations in the low-frequency meridional wind field on a time scale of 20-30 days. These variations affect the occurrence of heavy precipitation events in the lower reaches of the Yangtze River valley (LYRV). The results of 135 forecast experiments during the summer half year show that the predicted and observed anomalies are strongly correlated at a lead time of 20 days (mean correlation greater than 0.50). This strong correlation indicates that the model is capable of accurately forecasting the low-frequency variations in meridional wind that corresponded to the 3 heavy precipitation events in the LYRV during the summer of 2002. Further forecast experiments based on data from multiple years with significant 20-30-day oscillations show that these prediction modes are effective tools for forecasting the space-time evolution of the low-frequency circulation. These findings offer potential for improving the accuracy of forecasts of heavy precipitation over the LYRV at lead times of 3-4 weeks.  相似文献   

16.
Based on the daily precipitation data of nine stations representing the Xijiang River valley and the National Center for Environmental Prediction/National Center for Atmospheric Research (USA) reanalysis data, this study uses the wavelet analysis and band-pass filter methods to investigate the atmospheric intraseasonal oscillation characteristics of flood-causing rainstorms in the valley during the annually first raining seasons in 1968, 1994, 1998, 2002 and 2005. Results show that the daily precipitation in the valley exhibits significant quasi-biweekly (10 to 20 days) oscillations. The flood-causing rainstorms in the valley were mainly associated with the confluence of low-frequency warm and humid airflow in the lower latitudes and cold and dry airflow in the higher latitudes. The low-frequency vortexes were propagating or in control when this type of rainstorms took place over the valley, being favorable for the convergence of moisture at lower levels and thus vital to the formation of the rainstorms.  相似文献   

17.
The quasi-geostrophic atmospheric and oceanic equations of momentum and thermodynamics with dissipation factors are used to create a simple coupled ocean-atmosphere model describing the large-scale shallow-water motion. We discuss the ocean-atmosphere coupling effect in mid-high and low latitudes separately and analyze characteristics of which the oscillatory periods of coupled low-frequency modes (ocean mode) vary with the coupling frequency and latitudinal number. This can interpret the correlation between low-frequency oscillation and ocean-atmosphere interaction. Then from the dispersion curves of atmosphere and ocean, we reveal effect of the coupling strength on the propagation of Rossby waves. The convection mechanism between the two modes is also discussed in view of the slowly varying wave train.The results show that Newtonian cooling and Rayleigh friction play a stable rule in oceanic Rossby waves, the period of coupled low-frequency mode grows with the increment of the coupling frequency. The  相似文献   

18.
The South China Sea is a hotspot for regional climate research. Over the past 40 years, considerable im provement has been made in the development and utilization of the islands in the South China Sea, leading to a substantialchange in the land-use of the islands. However, research on the impact of human development on the local climate of theseislands is lacking. This study analyzed the characteristics of local climate changes on the islands in the South China Seabased on data from the Yongxing Island Observation Station and ERA5 re-analysis. Furthermore, the influence of urba nization on the local climate of the South China Sea islands was explored in this study. The findings revealed that the 10-year average temperature in Yongxing Island increased by approximately 1.11 °C from 1961 to 2020, and the contributionof island development and urbanization to the local warming rate over 60 years was approximately 36.2%. The linearincreasing trend of the annual hot days from 1961–2020 was approximately 14.84 days per decade. The diurnal tem perature range exhibited an increasing trend of 0.05 °C per decade, whereas the number of cold days decreased by 1.06days per decade. The rapid increase in construction on Yongxing Island from 2005 to 2021 led to a decrease in observedsurface wind speed by 0.32 m s –1 per decade. Consequently, the number of days with strong winds decreased, whereas thenumber of days with weak winds increased. Additionally, relative humidity exhibited a rapid decline from 2001 to 2016and then rebounded. The study also found substantial differences between the ERA5 re-analysis and observation data,particularly in wind speed and relative humidity, indicating that the use of re-analysis data for climate resource assessmentand climate change evaluation on island areas may not be feasible.  相似文献   

19.
In the present study, three wavelet basis functions (Mexican-hat, Morlet, and Wave) were used to analyze atmospheric turbulence data obtained from an eddy covariance system in order to determine effect of six meteorological elements (three-dimensional wind speed, temperature, and CO2 and H2O concentrations) on the time scale of coherent structures. First, we used the degree of correlation between original and reconstructed waveforms to test the three wavelets’ performance when determining the time scale of coherent structures. The Wave wavelet’s reconstructed coherent structure signal best matched the original signal; thus, it was used for further analysis of the time scale, number, and time cover of the meteorological elements. We found similar results for all elements, though there was some internal variation, suggesting that coherent structures are not inherently dependent on these elements. Our results provide a basis for proper coherent structure detection in atmospheric turbulence and improve the understanding of similarities and differences between coherent structure characteristics of different meteorological elements, which is helpful for further research into atmospheric turbulence and boundary layers.  相似文献   

20.
A barotropic channel model in β-plane is used to study the effect of topographic forcing on the formation and maintenance of blocking. The approximate analytical solution of potential vorticity equation can show the main property of the whole process of blocking. It is indicated that the topographic forcing is one of the main factors causing the blocking process. The results suggest that the nonlinear interaction plays a very important role in the stable "Ω" situation of blocking. The atmospheric circulation with periodic and low-frequency oscillation, perhaps, is partly caused by topographic forcing.  相似文献   

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