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Gao J.,Fujian Climate Center | Li T.,University of Hawaii at Manoa
Advances in Atmospheric Sciences | Year: 2012

The interannual variability of occurrence of multiple tropical cyclone (MTC) events during June-October in the western North Pacific (WNP) was examined for the period 1979-2006. The number of the MTC events ranged from 2 to 9 per year, exhibiting a remarkable year-to-year variation. Seven active and seven inactive MTC years were identified. Compared to the inactive years, tropical cyclone genesis locations extended farther to the east and in the meridional direction during the active MTC years. A composite analysis shows that inactive MTC years were often associated with the El Niño decaying phase, as warm SST anomalies in the equatorial eastern-central Pacific in the preceding winter transitioned into cold sea surface temperature (SST) anomalies in the concurrent summer. Associated with the SST evolution were suppressed low-level cyclonic vorticity and weakened convection in the WNP monsoon region. In addition to the mean flow difference, significant differences between active and inactive MTC years were also found in the strength of the atmospheric intraseasonal oscillation (ISO). Compared with inactive MTC years, ISO activity was much stronger along the equator and in the WNP region during active MTC years. Both westward- and northward-propagating ISO spectrums strengthened during active MTC years compared to inactive years. The combined mean state and ISO activity changes may set up a favorable environment for the generation of MTC events. © 2012 Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.

Hsu P.-C.,Nanjing University of Information Science and Technology | Hsu P.-C.,University of Hawaii at Manoa | Li T.,Nanjing University of Information Science and Technology | Li T.,University of Hawaii at Manoa | And 3 more authors.
Climate Dynamics | Year: 2015

Extended-range (10–30 days) forecast, lying between well-developed short-range weather and long-range (monthly and seasonal) climate predictions, is one of the most challenging forecast currently faced by operational meteorological centers around the world. In this study, a set of spatial–temporal projection (STP) models was developed to predict low-frequency rainfall events at lead times of 5–30 days. We focused on early monsoon rainy season (mid April–mid July) in South China. To ensure that the model developed can be used for real-time forecast, a non-filtering method was developed to extract the low-frequency atmospheric signals of 10–60 days without using a band-pass filter. The empirical models were built based on 12-year (1996–2007) data, and independent forecast was then conducted for a 5 year (2008–2012) period. The assessment of the 5-year forecast of rainfall over South China indicates that the ensemble prediction of the STP models achieved a useful skill (with a temporal correlation coefficient exceeding 95 % confidence level) at a lead time of 20 days. The amplitude error was generally less than one standard deviation at all lead times of 5–30 days. Furthermore, the STP models provided useful probabilistic forecasts with the ranked probability skill score between 0.3–0.5 up to 30-day forecast in advance. The evaluation demonstrated that the STP models exhibited useful 10–30 days forecast skills for real-time extended-range rainfall prediction in South China. © 2014, Springer-Verlag Berlin Heidelberg.

Zhu Z.,Nanjing University of Information Science and Technology | Zhu Z.,University of Hawaii at Manoa | Li T.,Nanjing University of Information Science and Technology | Li T.,University of Hawaii at Manoa | And 2 more authors.
Theoretical and Applied Climatology | Year: 2016

Based on outgoing longwave radiation (OLR), an index for clustering tropical cyclogenesis (CTC) over the western North Pacific (WNP) was defined. Around 76 % of total CTC events were generated during the active phase of the CTC index, and 38 % of the total active phase was concurrent with CTC events. For its continuous property, the CTC index was used as the representative predictand for extended-range forecasting the temporal distribution of CTC events. The predictability sources for CTC events were detected via correlation analyses of the previous 35–5-day lead atmospheric fields against the CTC index. The results showed that the geopotential height at different levels and the 200 hPa zonal wind over the global tropics possessed large predictability sources, whereas the predictability sources of other variables, e.g., OLR, zonal wind, and relatively vorticity at 850 hPa and relatively humility at 700 hPa, were mainly confined to the tropical Indian Ocean and western Pacific Ocean. Several spatial-temporal projection model (STPM) sets were constructed to carry out the extended-range forecast for the CTC index. By combining the output of STPMs separately conducted for the two dominant modes of intraseasonal variability, e.g., the 10–30 and the 30–80 day mode, useful forecast skill could be achieved for a 30-day lead time. The combined output successfully captured both the 10–30 and 30–80 day mode at least 10 days in advance. With a relatively low rate of false alarm, the STPM achieved hits for 80 % (69 %) of 54 CTC events during 2003–2014 at the 10-day (20-day) lead time, suggesting a practical value of the STPM for real-time forecasting WNP CTC events at an extended range. © 2016 Springer-Verlag Wien

Yin Y.,CAS Institute of Atmospheric Physics | Yin Y.,National Climate Center | Gemmer M.,National Climate Center | Luo Y.,National Climate Center | Wang Y.,Fujian Climate Center
Quaternary International | Year: 2010

Tropical cyclones (TCs) are historically documented along the coastline of China. They can have negative impacts on society and damages are reported annually. This paper examines to what extent TCs are responsible for heavy rain days (precipitation > 100 mm/d) in coastal Fujian Province. The average deviation of TCs making landfall in China is 25%, and they occur more reliably than TCs in the west North Pacific. A distinct typhoon season between July and September/October was detected and can be explained by low interannual variability during these months.The annual number of TCs is below average (above average) during El Niño (La Niña) years, but the intensity of TCs is higher during El Niño years. From 1960 to 2007, 41% of heavy rain days (precipitation > 100 mm/d) at all 66 weather stations in Fujian Province were triggered by TCs. The number of heavy rain days is higher during El Niño years, although the number of TCs affecting Fujian in general is higher during La Niña years. For the coastal weather stations in east Fujian, 57% (45%) of the heavy rain days are triggered by TCs during El Niño (La Niña) years. In the research area, more than 50% of annual heavy rain days can be explained by TCs, and the ratio reaches 85% in the northern part bordering Zhejiang Province. More TCs impact Fujian during La Niña years, but more TCs cause heavy precipitation days during El Niño years. The number of heavy rain days fluctuates in line with the interannual variability of TCs making landfall. © 2010 Elsevier Ltd and INQUA.

Zou Y.,Chinese Academy of Meteorological Sciences | Zou Y.,Fujian Climate Center | Zhao P.,National Meteorological Information Center
Journal of Tropical Meteorology | Year: 2010

This is a study to compare three selected tropical cyclone datasets separately compiled by CMA Shanghai Typhoon Institute (CMA SHI), the Joint Typhoon Warning Center (JTWC), and the Japan Meteorological Agency (JMA). The annual frequencies, observation times and destructive power index as the characteristic quantities are investigated of the tropical cyclones over the western North Pacific. The comparative study has resulted in the following findings: 1) Statistical gaps between the datasets compared are narrowing down as the intensity of tropical cyclones increases. 2) In the context of interdecadal distribution, there is for the 1950s a relatively large gap between the datasets, as compared with a narrowed gap for the period from the mid 1970s to the 1980s, and a recurring widened gap for the mid and late 1990s. Additionally, an approach is proposed in the paper to correct the wind speed data in the TC Yearbook.

Cai J.,Nanjing University of Information Science and Technology | Guan Z.,Nanjing University of Information Science and Technology | Gao Q.,Nanjing University of Information Science and Technology | Lin X.,Fujian Climate Center | Qian D.,Nanjing University of Information Science and Technology
Journal of Geographical Sciences | Year: 2010

Using the daily data of temperature from China Meteorological Administration and the NCEP/NCAR reanalysis from 1960 to 2005, we have analyzed the relationships between the summertime high/low temperature events in the middle and lower reaches of the Yangtze River (MLRYR) and the related circulation anomalies in the Eastern Hemisphere. Our results have demonstrated that a significantly increasing trend is observed in daily minimum temperature in the past 50 years. And in some regions in the Northern Hemisphere, the opposite scenarios are observed in circulation anomalies in lower and upper parts of the troposphere in the years when the temperatures are higher than normal, as compared to those in the years when the temperatures are lower than normal in the middle and lower reaches of the Yangtze River (MLRYR). Additionally, the anomalous circulation structure in vertical direction in both the high and lower temperature years are barotropic. It is found that the emergence and maintenance of the aforementioned anomalous circulations are related to three kinds of wave train teleconnection patterns. Further more, influences of the long wave surface radiation on the air temperature are stronger in the nighttime than that in the daytime. While both the maximum and minimum temperatures have negative relationships with the sensible heat flux but positive relationships with the latent heat flux. To some extent, the anomalous dynamic heating (cooling) caused by the vertical thermal advection as well as the diabatic heating (cooling) caused by diabatic processes can explain the formation of the high (low) temperature events in the middle and lower reaches of the Yangtze River (MLRYR) in boreal summer. © 2010 Science in China Press and Springer-Verlag Berlin Heidelberg.

Zhang R.,Fujian Climate Center | Zhang R.,Institute of Meteorological Science of Fujian Province | Zhang X.,National Climate Center | Xu Z.,Institute of Meteorological Science of Fujian Province | Xu J.,Nanjing University of Information Science and Technology
Taiyangneng Xuebao/Acta Energiae Solaris Sinica | Year: 2014

By studying daily 10 minute interval wind data during 29 tropical cyclones (TC) measured by 88 wind tower since 2003, it is found that the turbulence intensity at TC center and nearby exceeds the IEC standards. Especially wind speed is up to 16-29 m/s, the maximum exceeds the standard by 0.04. The normal turbulence model (NTM) in IEC standard can not fully describe the status in typhoon center and nearby area. NTM expression in the TC center and nearby is. Turbulence intensity A, B and C classes have been defined as 0.18, 0.16 and 0.14, respectively; higher levels of turbulence intensity class is defined as 0.20.

Gao J.,Fujian Climate Center | Li T.,University of Hawaii at Manoa
Monthly Weather Review | Year: 2011

The statistical feature of occurrence of multiple tropical cyclone (MTC) events in the western North Pacific (WNP) is examined during summer (June-September) for the period of 1979-2006. The number of MTC events ranged from one to eight per year, experiencing a marked interannual variation. The spatial distance between the TCs associated with MTC events is mostly less than 3000 km, which accounts for 73% of total samples. The longest active phase of an MTC event lasts for nine days, and about 80% of the MTC events last for five days or less. A composite analysis of active and inactive MTC phases reveals that positive low-level (negative upper-level) vorticity anomalies and enhanced convection and midtropospheric relative humidity are the favorable large-scale conditions for MTC genesis. About 77% of the MTC events occurred in the region where either the atmospheric intraseasonal (25-70 day) oscillation (ISO) or biweekly (10-20 day) oscillation (BWO) is in a wet phase. The overall occurrence of the MTC events is greatly regulated by the combined large-scale impact of BWO, ISO, and the lower-frequency (90 days or longer) oscillation. On the interannual time scale, the MTC frequency is closely related to the seasonal mean anomalies of 850-hPa vorticity, outgoing longwave radiation (OLR), and 500-hPa humidity fields. The combined ISO and BWO activity is greatly strengthened (weakened) in the WNP region during the MTC active (inactive) years. © 2011 American Meteorological Society.

Gao J.,Fujian Climate Center | Lin H.,Environment Canada | You L.,Fujian Climate Center | Chen S.,Fujian Climate Center
Climate Dynamics | Year: 2016

Rainfall variability during the early-flood season (April–June) in South China is largely controlled by both the 10–20 and 20–70-day intraseasonal oscillations (ISO). In this study, a method is described to monitor the ISO and persistent heavy rainfall in South China. Three existing daily real-time 20–70-day ISO indices are compared. It is found that the regional East Asia–western North Pacific (EAWNP) ISO index best represents the early-flood season 20–70-day ISO in South China. A new bivariate boreal summer ISO index is designed to describe the 10–20-day ISO in the EAWNP region. Composite analysis shows that the rainfall anomaly in South China is well captured by the northward propagation of both the 10–20 and 20–70-day ISO. With different phase combinations of the 10–20 and 20–70-day EAWNP ISO, nine conditions are defined ranging from those favorable to those unfavorable to heavy rainfall in South China that can be used to effectively monitor the early-flood season ISO and persistent heavy rainfall in South China. © 2016 Springer-Verlag Berlin Heidelberg

Sun P.,Hubei Meteorological Service Center | Chen Z.,Hubei Meteorological Service Center | Cheng C.,Hubei Meteorological Service Center | Bai L.,Fujian Climate Center | Zhang X.,Hubei Meteorological Service Center
Taiyangneng Xuebao/Acta Energiae Solaris Sinica | Year: 2015

Model output statistics (MOS) is a relatively simple and reliable method for forecasting solar radiation. Based on improved conventional MOS method, a improved radiation forecast model was set up to improve the forecasting effect. Considering the weakening effect of atmosphere on radiation, the actual radiation was converted to articulation index to remove astronomical solar radiation impact. Besides, owing to greater impacts of different weather conditions on solar radiation, weather type was classified by using Fisher method before modeling. Meteorological elements of the same weather type, at the same times and in the same season were regarded as a same type. Considering weight changes of solar radiation elements resulted by seasonal and diurnal change characteristics of the solar radiation, the forecast model for different seasons and different times was built. Finally, considering the continuity of the system error, the error of initial model forecast value and the actual value could be regarded as a variable which would be used to build later hours forecast equation. The results show that the analog values of the model can reflect the actual changes in solar radiation and meet the modeling requirement. The mean absolute percentage error (MAPE) of improved MOS model is about 20% less than that of conventional MOS model, significantly improving the forecasting results. August 2012 as the forecast period, the MAPE is 28.33% in forecast period, and the rRMSE is 16.20%. These results show a good prediction skill of the model. © 2015, Science Press. All right reserved.

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