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Adjoint Sensitivity Study on Idealized Explosive Cyclogenesis

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Journal of Meteorological Research 2016年第4期30卷 547-558页

作者：储可宽张熠 key laboratory of mesoscale severe weather/ministry of education and School of Atmospheric SciencesNanjing University

The adjoint sensitivity related to explosive cyclogenesis in a conditionally unstable atmosphere is investigated in this study.The PSU/NCAR limited-area,nonhydrostatic primitive equation numerical model MM5 and its adjoint system are employed for numerical simulation and adjoint computation,respectively.To ensure the explosive development of a baroclinic wave,the forecast model is initialized with an idealized condition including an idealized two-dimensional baroclinic jet with a balanced three-dimensional moderateamplitude disturbance,derived from a potential vorticity inversion technique.Firstly,the validity period of the tangent linear model for this idealized baroclinic wave case is discussed,considering different initial moisture distributions and a dry condition.Secondly,the 48-h forecast surface pressure center and the vertical component of the relative vorticity of the cyclone are selected as the response functions for adjoint computation in a dry and moist environment,respectively.The preliminary results show that the validity of the tangent linear assumption for this idealized baroclinic wave case can extend to 48 h with intense moist convection,and the validity period can last even longer in the dry adjoint integration.Adjoint sensitivity analysis indicates that the rapid development of the idealized baroclinic wave is sensitive to the initial wind and temperature perturbations around the steering level in the upstream.Moreover,the moist adjoint sensitivity can capture a secondary high sensitivity center in the upper troposphere,which cannot be depicted in the dry adjoint run.

关键词： baroclinic wave explosive niidlatitude cyclone adjoint sensitivity potential vorticity inversion

Determining Atmospheric Boundary Layer Height with the Numerical Differentiation Method Using Bending Angle Data from COSMIC

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Advances in Atmospheric Sciences 2019年第3期36卷 303-312,340页

作者： Shen YAN Jie XIANG Huadong DU College of Meteorology and Oceanography National University of Defense Technology key laboratory of mesoscale severe weather of ministry of education

This paper presents a new method to estimate the height of the atmospheric boundary layer(ABL) by using COSMIC radio occultation bending angle(BA) data. Using the numerical differentiation method combined with the regularization technique, the first derivative of BA profiles is retrieved, and the height at which the first derivative of BA has the global minimum is defined to be the ABL height. To reflect the reliability of estimated ABL heights, the sharpness parameter is introduced, according to the relative minimum of the BA derivative. Then, it is applied to four months of COSMIC BA data(January, April, July, and October in 2008), and the ABL heights estimated are compared with two kinds of ABL heights from COSMIC products and with the heights determined by the finite difference method upon the refractivity data. For sharp ABL tops(large sharpness parameters), there is little difference between the ABL heights determined by different methods, i.e.,the uncertainties are small; whereas, for non-sharp ABL tops(small sharpness parameters), big differences exist in the ABL heights obtained by different methods, which means large uncertainties for different methods. In addition, the new method can detect thin ABLs and provide a reference ABL height in the cases eliminated by other methods. Thus, the application of the numerical differentiation method combined with the regularization technique to COSMIC BA data is an appropriate choice and has further application value.

关键词：大气边界层高度数值微分方法 COSMIC 弯角正则化

Environmental Influences on the Intensity Change of Tropical Cyclones in the Western North Pacific

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Acta meteorologica Sinica 2013年第3期27卷 335-343页

作者：储惠芸伍荣生 key laboratory of mesoscale severe weather/ministry of education and School of Atmospheric Sciences Nanjing University key laboratory of mesoscale severe weather/ministry of education and School of Atmospheric SciencesNanjing University

The atmospheric and oceanic conditions are examined during different stages of the lifecycle of western North Pacific tropical cyclones （TCs）, with the intention to understand how the environment affects the intensity change of TCs in this area. It is found that the intensification usually occurs when the underlying sea surface temperature （SST） is higher than 26℃. TCs usually experience a rapid intensification when the SST is higher than 27.5℃ while lower than 29.5℃. However, TCs decay or only maintain its intensity when the SST is lower than 26℃. The intensifying TCs usually experience a low-to-moderate vertical wind shear （2-10 m s-l）. The larger the vertical wind shear, the slower the TCs strengthen. In addition, the convective available potential energy （CAPE） is much smaller in the developing stage than in the formation stage of TCs. For the rapidly intensifying TCs, the changes of SST, CAPE, and vertical wind shear are usually small, indicating that the rapid intensification of TCs occurs when the evolution of the environment is relatively slow.

关键词： tropical cyclone sea surface temperature convective available potential energy vertical windshear

Favorable Environments for the Occurrence of Overshooting Tops in Tropical Cyclones

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Advances in Atmospheric Sciences 2017年第4期34卷 532-544页

作者： Liangxiao SUN Xiaoyong ZHUGE Yuan WANG School of Atmospheric Sciences and key laboratory of mesoscale severe weather of ministry of education Nanjing UniversityNanjing 210023China

Based on Multifunctional Transport Satellite data and the infrared window-texture detection algorithm, the level of overshooting top（OT） activity within a tropical cyclone（TC）, which is defined as the hourly mean number of OT occurrence,was statistically investigated in the western North Pacific basin for the period 2005–12. Based on the level of OT activity,the samples were divided into OT and non-OT cases or high-activity-OT（HA-OT） and low-activity-OT（LA-OT） cases. The differences in large-scale environmental variables between OT（HA-OT） and non-OT（LA-OT） cases were examined 12 hours prior to the OT occurrence. Statistical analysis showed that environmental differences did exist between the OT and non-OT cases. The OTs were more skewed towards the early stage of the TC life cycle, and mostly concentrated in low latitudes.Meanwhile, a sufficiently deep warm-water layer, large temperature difference between the upper- and lower-level troposphere, large humidity at the middle and upper levels, and large atmospheric instability, were favorable for OT occurrence.The differences in large-scale environmental characteristics between HA-OTs and LA-OTs were not as significant as those between OTs and non-OTs, but the HA-OT samples tended to occur when the vertical shear was weak and the TC intensity was low. Finally, statistical models were designed to predict the OT and HA-OT. When at least three OT（HA-OT） predictor thresholds were satisfied, the Peirce skill score reached a maximum value of 0.49（0.30）.

关键词： overshooting top geostationary satellite tropical cyclone western North Pacific

Atypical Occlusion Process Caused by the Merger of a Sea-breeze Front and Gust Front

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Advances in Atmospheric Sciences 2015年第10期32卷 1431-1443页

作者： Abuduwaili ABULIKEMU XU Xin WANG Yuan DING Jinfeng WANG Yan key laboratory of mesoscale severe weather(ministry of education) School of Atmospheric SciencesNanjing University Tianjin weather Modification Office

An atypical occlusion process that occurred in North China on 14 July 2011 is studied based on both observations and a real-data weather Research and Forecasting （WRF） model simulation. The results show that this atypical occlusion process was significantly different from the traditional, synoptic-scale occlusion process that occurs within extratropical cyclones. It was caused by the merger of two cold-type mesoscale fronts. One of the fronts developed from the gust front of convective storms, while the other was a sea-breeze front. As the two fronts moved towards each other, the warm air between them was squeezed and separated from the surface. An atypical occluded front was formed when the two fronts merged, with the warm air forced aloft. This kind of occlusion is termed a ＂merger＂ process, different from the well-known ＂catch-up＂ and ＂wrap-up＂ processes. Moreover, local convection was found to be enhanced during the merger process, with severe convective weather produced in the merger area.

关键词： occlusion process sea-breeze front gust front merger

Observation of a Straight-Line Wind Case Caused by a Gust Front and Its Associated Fine-Scale Structures

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Journal of Meteorological Research 2014年第6期28卷 1137-1154页

作者：权婉晴徐昕王元 key laboratory of mesoscale severe weather of ministry of education School of Atmospheric SciencesNanjing University

A straight-line wind case was observed in Tianjin on 13 June 2005,which was caused by a gust front from a squall line.mesoscale analyses based on observations from in-situ surface stations,sounding,and in-situ radar as well as fine-scale analyses based on observation tower data were performed.The mesoscale characteristics of the gust front determined its shape and fine-scale internal structures.Based on the scale and wavelet analyses,the fine-scale structures within the gust front were distinguished from the classical mesoscale structures,and such fine-scale structures were associated with the distribution of straight-line wind zones.A series of cross-frontal fine-scale circulations at the lowest levels of the gust front was discovered,which caused a relatively weak wind zone within the frontal strong wind zone.The downdraft at the rear of the head region of the gust front was more intense than in the classical model,and similar to the microburst,a series of vertical vortices propagated from the rear region to the frontal region.In addition,strong tangential fine-scale instability was detected in the frontal region.Finally,a fine-scale gust front model with straight-line wind zones is presented.

关键词： straight-line wind gust front fine scale squall line

IMPACTS OF DIFFERENT KINDS OF ENSO ON LANDFALLING TROPICAL CYCLONES IN CHINA

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Journal of Tropical Meteorology 2013年第1期19卷 39-48页

作者：杜予罡宋金杰汤剑平 key laboratory of mesoscale severe weather/ministry of education and School of Atmospheric SciencesNanjing University

Interannual variability of landfalling tropical cyclones(TCs) in China during 1960-2010 is investigated.By using the method of partial least squares regression(PLS-regression),canonical ENSO and ENSO Modoki are identified to be the factors that contribute to the interannual variability of landfalling TCs.El Ni o Modoki years are associated with a greater-than-average frequency of landfalling TCs in China,but reversed in canonical El Ni o years.Significant difference in genesis locations of landfalling TCs in China for the two kinds of El Ni o phases occurs dominantly in the northern tropical western North Pacific(WNP).The patterns of low-level circulation anomalies and outgoing longwave radiation(OLR) anomalies associated with landfalling TC genesis with different types of El Ni o phases are examined.During canonical El Ni o years,a broad zonal band of positive OLR anomalies dominates the tropical WNP,while the circulation anomalies exhibit a meridionally symmetrical dipole pattern with an anticyclonic anomaly in the subtropics and a cyclonic anomaly near the tropics.In El Ni o Modoki years,a vast region of negative OLR anomalies,roughly to the south of 25°N with a strong large-scale cyclonic anomaly over the tropical WNP,provides a more favorable condition for landfalling TC genesis compared to its counterpart during canonical El Ni o years.For more landfalling TCs formed in the northern tropical WNP in El Ni o Modoki years,there are more TCs making landfall on the northern coast of China in El Ni o Modoki years than in canonical El Ni o years.The number of landfalling TCs is slightly above normal in canonical La Ni a years.Enhanced convection is found in the South China Sea(SCS) and the west of the tropical WNP,which results in landfalling TCs forming more westward in canonical La Ni a years.During La Ni a Modoki years,the landfalling TC frequency are below normal,owing to an unfavorable condition for TC genesis persisting in a broad zonal band from 5°N to 25°N.Since the western North Pacific subtropical high(W

关键词： landfalling tropical cyclone interannual variability canonical ENSO ENSO Modoki PLS-regression

Impact of the Subtropical High on the Extratropical Transition of Tropical Cyclones over the Western North Pacific

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Acta meteorologica Sinica 2013年第4期27卷 476-485页

作者：宋金杰伍荣生权婉晴杨程 key laboratory of mesoscale severe weather/ministry of education and School of Atmospheric Sciences Nanjing University

Recent publications have investigated the interactions between the extratropical transitions （ETs） of tropical cyclones （TCs） and midlatitude circulations; however, studies of ET events have rarely considered the relationship between the storm and the nearby subtropical high. The TC best-track data provided by the Regional Specialized Meteorological Center-Tokyo Typhoon Center of the Japan Meteorology Agency are used in conjunction with the NCEP/NCAR reanalysis data to discuss the potential effects of the subtropical high on ETs over the western North Pacific basin. When the western Pacific subtropical high （WPSH） is weakened and withdrawn toward the east, more TCs follow recurving paths and the midlatitude trough activity is intensified. These changes lead to enhanced ET activity. By contrast, when the WPSH strengthens and extends westward, the number of TCs that follow direct westward paths increases and the midlatitude trough is relatively inactive. These conditions lead to reduced occurrences of ET cases. Abnormal activity of the WPSH should be considered as an important factor in determining ET activity.

关键词： tropical cyclone extratropical transition western Pacific subtropical high

Evaluation of a Regional Ensemble Data Assimilation System for Typhoon Prediction

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Advances in Atmospheric Sciences 2022年第11期39卷 1816-1832页

作者： Lili LEI Yangjinxi GE Zhe-Min TAN Yi ZHANG Kekuan CHU Xin QIU Qifeng QIAN key laboratory of mesoscale severe weather/ministry of education School of Atmospheric SciencesNanjing UniversityNanjing 210063China National Meteorological Center China Meteorological AdministrationBeijing 100081China

An ensemble Kalman filter(EnKF) combined with the Advanced Research weather Research and Forecasting model(WRF) is cycled and evaluated for western North Pacific(WNP) typhoons of year 2016. Conventional in situ data, radiance observations, and tropical cyclone(TC) minimum sea level pressure(SLP) are assimilated every 6 h using an 80-member ensemble. For all TC categories, the 6-h ensemble priors from the WRF/EnKF system have an appropriate amount of variance for TC tracks but have insufficient variance for TC intensity. The 6-h ensemble priors from the WRF/EnKF system tend to overestimate the intensity for weak storms but underestimate the intensity for strong storms. The 5-d deterministic forecasts launched from the ensemble mean analyses of WRF/EnKF are compared to the NCEP and ECMWF operational control forecasts. Results show that the WRF/EnKF forecasts generally have larger track errors than the NCEP and ECMWF forecasts for all TC categories because the regional simulation cannot represent the large-scale environment better than the global simulation. The WRF/EnKF forecasts produce smaller intensity errors and biases than the NCEP and ECMWF forecasts for typhoons, but the opposite is true for tropical storms and severe tropical storms. The 5-d ensemble forecasts from the WRF/EnKF system for seven typhoon cases show appropriate variance for TC track and intensity with short forecast lead times but have insufficient spread with long forecast lead times. The WRF/EnKF system provides better ensemble forecasts and higher predictability for TC intensity than the NCEP and ECMWF ensemble forecasts.

关键词： ensemble Kalman filter typhoon prediction ensemble forecast