The authors apply the technique of conditional nonlinear optimal perturbations （CNOPs） as a means of providing initial perturbations for ensemble forecasting by using a barotropic quasi-geostrophic （QG） model in a...The authors apply the technique of conditional nonlinear optimal perturbations （CNOPs） as a means of providing initial perturbations for ensemble forecasting by using a barotropic quasi-geostrophic （QG） model in a perfect-model scenario. Ensemble forecasts for the medium range （14 days） are made from the initial states perturbed by CNOPs and singular vectors （SVs）. 13 different cases have been chosen when analysis error is a kind of fast growing error. Our experiments show that the introduction of CNOP provides better forecast skill than the SV method. Moreover, the spread-skill relationship reveals that the ensemble samples in which the first SV is replaced by CNOP appear superior to those obtained by SVs from day 6 to day 14. Rank diagrams are adopted to compare the new method with the SV approach. The results illustrate that the introduction of CNOP has higher reliability for medium-range ensemble forecasts.展开更多
In this paper, the approach proposed by Mu and Jiang （2008） to obtain the optimal perturbations for triggering blocking （BL） onset is generalized to seek the optimal perturbations triggering onset of the strong zo...In this paper, the approach proposed by Mu and Jiang （2008） to obtain the optimal perturbations for triggering blocking （BL） onset is generalized to seek the optimal perturbations triggering onset of the strong zonal flow （SZF） regime. The BL and SZF regimes are characterized by the same dipole-like anomaly pattern superposed on the climatological flow, but with opposite sign. The results show that this method is also superior at finding the initial optimal perturbations triggering onset of the SZF regime, especially in the medium range. Furthermore, by comparing the two kinds of conditional nonlinear optimal perturbations （CNOPs） trig-gering onset of BL and SZF regimes, we find that in the linear approximation, there is symmetry in the sensitivities for BL and SZF onset, and the perturbations that optimally trigger onset of BL and SZF regimes at times when linear approximation is valid are also characterized by the same spatial pattern but with opposite sign. Whereas when the optimization time is extended to 6 days, the two kinds of CNOPs lose their out-of-phase behavior. The nonlinearity results in an asymmetry between the sensitivity for BL and SZF onset. Additionally, we find that the optimal perturbations have one common property, which is that the second baroclinic mode contributes more to the initial perturbations while the barotropic mode dominates the final structures.展开更多
In this paper the optimal precursors for wintertime Eurasian blocking onset are acquired by solving a nonlinear optimization problem whose objective function is constructed based on a blocking index with a triangular ...In this paper the optimal precursors for wintertime Eurasian blocking onset are acquired by solving a nonlinear optimization problem whose objective function is constructed based on a blocking index with a triangular T21, three-level, quasi-geostrophic global spectral model. The winter climatological state is chosen as the reference basic state. Numerical results show that the optimal precursors are characterized by a baroclinic pattern with a westward tilt with height, which are mainly located upstream of the blocking region. For an optimization time of 5 days, these perturbations are mainly localized over the Northeast Atlantic Ocean and continental Europe. With the extension of the optimization time to 8 days, these perturbations are distributed more upstream and extensively in the zonal direction. Wave spectrum analysis reveals that the optimal precursors are composed of not only synoptic-scale （wave numbers 5-18） waves, but planetary-scale （wave numbers 0-4） waves as well. The synoptic-scale optimal precursors are mainly located in the mid-latitude area, while the planetary-scale optimal precursors focus primarily on the high- latitude region. The formation of a strong planetary-scale positive blocking anomaly is accompanied by the reinforcement of synoptic-scale perturbations and further fragmentation into two branches, in which the northern branch is generally stronger than the southern one. The eddy forcing arising from the selfinteraction of synoptic-scale disturbances is shown to be crucial in triggering the dipole blocking anomaly, and the planetary-scale optimal precursor provides the initial favorable background conditions for blocking onset.展开更多
A two-layer quasi-geostrophic model is used to study the stability and sensitivity of motions on smallscale vortices in Jupiter＇s atmosphere. Conditional nonlinear optimal perturbations （CNOPs） and linear singular ...A two-layer quasi-geostrophic model is used to study the stability and sensitivity of motions on smallscale vortices in Jupiter＇s atmosphere. Conditional nonlinear optimal perturbations （CNOPs） and linear singular vectors （LSVs） are both obtained numerically and compared in this paper. The results show that CNOPs can capture the nonlinear characteristics of motions in small-scale vortices in Jupiter＇s atmosphere and show great difference from LSVs under the condition that the initial constraint condition is large or the optimization time is not very short or both. Besides, in some basic states, local CNOPs are found. The pattern of LSV is more similar to local CNOP than global CNOP in some cases. The elementary application of the method of CNOP to the Jovian atmosphere helps us to explore the stability of variousscale motions of Jupiter＇s atmosphere and to compare the stability of motions in Jupiter＇s atmosphere and Earth＇s atmosphere further.展开更多
Since the last International Union of Geodesy and Geophysics General Assembly （2003）, predictability studies in China have made significant progress. For dynamic forecasts, two novel approaches of conditional nonlin...Since the last International Union of Geodesy and Geophysics General Assembly （2003）, predictability studies in China have made significant progress. For dynamic forecasts, two novel approaches of conditional nonlinear optimal perturbation and nonlinear local Lyapunov exponents were proposed to cope with the predictability problems of weather and climate, which are superior to the corresponding linear theory. A possible mechanism for the ＂spring predictability barrier＂ phenomenon for the E1 Nifio-Southern Oscillation （ENSO） was provided based on a theoretical model. To improve the forecast skill of an intermediate coupled ENSO model, a new initialization scheme was developed, and its applicability was illustrated by hindcast experiments. Using the reconstruction phase space theory and the spatio-temporal series predictive method, Chinese scientists also proposed a new approach to improve dynamical extended range （monthly） prediction and successfully applied it to the monthly-scale predictability of short-term climate variations. In statistical forecasts, it was found that the effects of sea surface temperature on precipitation in China have obvious spatial and temporal distribution features, and that summer precipitation patterns over east China are closely related to the northern atmospheric circulation. For ensemble forecasts, a new initial perturbation method was used to forecast heavy rain in Guangdong and Fujian Provinces on 8 June 1998. Additionally, the ensemble forecast approach was also used for the prediction of a tropical typhoons. A new downscaling model consisting of dynamical and statistical methods was provided to improve the prediction of the monthly mean precipitation. This new downscaling model showed a relatively higher score than the issued operational forecast.展开更多
In this paper, a nonlinear optimization method is used to explore the finite-time instability of the atmospheric circulation with a three-level quasigeostrophic model under the framework of the conditional nonlinear o...In this paper, a nonlinear optimization method is used to explore the finite-time instability of the atmospheric circulation with a three-level quasigeostrophic model under the framework of the conditional nonlinear optimal perturbation （CNOP）. As a natural generalization of linear singular vector （SV）, CNOP is defined as an initial perturbation that makes the cost function the maximum at a prescribed forecast time under certain physical constraint conditions. Special attentions are paid to the different structures and energy evolutions of the optimal perturbations. The results show that the most instable region of the global atmospheric circulation lies in the midlatitude Eurasian continent. More specially, SV and CNOP in the total energy norm with an optimization time of 2 days both present localness： they are mainly located in the midlatitude Asian continent and its east coast. With extension of the optimization time, SVs are more upstream and less localized in the zonal direction, and CNOPs differ essentially from SVs with broader zonal and meridional coverages; as a result, CNOPs acquire larger kinetic and available potential energy amplifications than SVs in the nonlinear model at the corresponding optimization time. For the climatological wintertime flow, it is seen that the baroclinic terms remain small over the entire time evolution, and the energy production comes essentially from the eddy kinetic energy, which is induced by the horizontal shear of the basic flow. In addition, the effects of SVs and CNOPs on the Eurasian atmospheric circulation are explored. The results show that the weather systems over the Eurasian continent in the perturbed fields by CNOPs are stronger than those by SVs at the optimization time. This reveals that the CNOP method is better in evaluating the instability of the atmospheric circulation while the SV method underestimates the possibility of extreme weather events.展开更多
Four successive freezing rain/heavy snowfall processes occurred in the southern part of China from 11 January to 2 February 2008 （named ＂0801 Southern Snow Disaster＂ hereafter）, during which a large-scale blocking...Four successive freezing rain/heavy snowfall processes occurred in the southern part of China from 11 January to 2 February 2008 （named ＂0801 Southern Snow Disaster＂ hereafter）, during which a large-scale blocking circulation lasted for a long time over the mid-high latitudes of the Euro-Asian continent. This severe event is featured with a broad spatial scale, strong intensity, long duration, and serious damage. During the event, the blocking situation in the mid-high latitudes maintained quasi-sationary, but weather systems in the lower latitudes were active. Abundant water vapor was supplied, and favorable weather conditions for ice storms were formed over the large areas across the southern part of China. The results in this paper demonstrate that the significant factors responsible for the abnormal atmospheric circulation and this severe event include： 1） the very active Arctic Oscillation （AO）, which helped the permanent maintenance of the planetary-scale waves; 2） the continuous transfer of negative vorticity from the upstream region around 50°E into the blocking area, which caused the blocking situation reinforced repeatedly and sustained for a long time; and 3） the active air currents south of the Tibetan Plateau, which ensured abundant moisture supply to the southern areas of China. The 0801 Southern Snow Disaster was accompanied by extremely severe icing. In this paper, the data from Cloud-Profile Radar onboard the satellite CloudSat are used to study the dynamic and microphysical features of this event. The results show that there existed a melting layer between 2 and 4 km, and ice particles could be found above this layer and in the layer near the ground surface. Surface temperature kept between -4℃ and 0℃ with relative humidity over 90%, which provided the descending supercooled waterdrops with favorable synoptic and physical conditions to form glaze and ice at the surface via freezing, deposition and/or accretion. Causes of the event might be, as a whole, traced back to the planetary-scale systems. The study on the polar vortex anomaly in this paper reveals that changes in the polar vortex in the stratosphere preceded those in the troposphere, especially in early December 2007, while the intensification of the polar vortex in the troposphere delayed dramatically until middle January and early February of 2008. This implies that changes in the polar vortex in the stratosphere may be a precursor of the ensuing severe event and a meaningful clue for extended forecasts of such a disaster.展开更多
This paper reviews progress in the application of conditional nonlinear optimal perturbation to targeted observation studies of the atmosphere and ocean in recent years, with a focus on the E1 Nifio-Southern Oscillati...This paper reviews progress in the application of conditional nonlinear optimal perturbation to targeted observation studies of the atmosphere and ocean in recent years, with a focus on the E1 Nifio-Southern Oscillation （ENSO）, Kuroshio path variations, and blocking events. Through studying the optimal precursor （OPR） and optimally growing initial error （OGE） of the occurrence of the above events, the similarity and localization features of OPR and OGE spatial structures have been found for each event. Ideal hindcasting experiments have shown that, if initial errors are reduced in the areas with the largest amplitude for the OPR and OGE for ENSO and Kuroshio path variations, the forecast skill of the model for these events is significantly improved. Due to the similarity between patterns of the OPR and OGE, additional observations implemented in the same sensitive region would help to not only capture the precursors, but also reduce the initial errors in the predictions, greatly increasing the forecast abilities. The similarity and localization of the spatial structures of the OPR and OGE during the onset of blocking events have also been investigated, but their application to targeted observation requires further study.展开更多
基金supported by State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences Program for Basic Research of China (No. 2008LASWZI01)the Chinese Academy of Sciences (Grant No. KZCX3-SW-230)the National Natural Science Foundation of China (Grant No. 40675030)
文摘The authors apply the technique of conditional nonlinear optimal perturbations （CNOPs） as a means of providing initial perturbations for ensemble forecasting by using a barotropic quasi-geostrophic （QG） model in a perfect-model scenario. Ensemble forecasts for the medium range （14 days） are made from the initial states perturbed by CNOPs and singular vectors （SVs）. 13 different cases have been chosen when analysis error is a kind of fast growing error. Our experiments show that the introduction of CNOP provides better forecast skill than the SV method. Moreover, the spread-skill relationship reveals that the ensemble samples in which the first SV is replaced by CNOP appear superior to those obtained by SVs from day 6 to day 14. Rank diagrams are adopted to compare the new method with the SV approach. The results illustrate that the introduction of CNOP has higher reliability for medium-range ensemble forecasts.
基金supported by the National Natural Science Foundation of China (Grant Nos 40905023 and 40633016)the State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences Program for Basic Research of China (No2008LASWZI01)
文摘In this paper, the approach proposed by Mu and Jiang （2008） to obtain the optimal perturbations for triggering blocking （BL） onset is generalized to seek the optimal perturbations triggering onset of the strong zonal flow （SZF） regime. The BL and SZF regimes are characterized by the same dipole-like anomaly pattern superposed on the climatological flow, but with opposite sign. The results show that this method is also superior at finding the initial optimal perturbations triggering onset of the SZF regime, especially in the medium range. Furthermore, by comparing the two kinds of conditional nonlinear optimal perturbations （CNOPs） trig-gering onset of BL and SZF regimes, we find that in the linear approximation, there is symmetry in the sensitivities for BL and SZF onset, and the perturbations that optimally trigger onset of BL and SZF regimes at times when linear approximation is valid are also characterized by the same spatial pattern but with opposite sign. Whereas when the optimization time is extended to 6 days, the two kinds of CNOPs lose their out-of-phase behavior. The nonlinearity results in an asymmetry between the sensitivity for BL and SZF onset. Additionally, we find that the optimal perturbations have one common property, which is that the second baroclinic mode contributes more to the initial perturbations while the barotropic mode dominates the final structures.
基金supported by the National Natural Science Foundation of China(Grant No.40905023)the National Key Basic Research and Development(973) Project(Grant No. 2012CB417200)
文摘In this paper the optimal precursors for wintertime Eurasian blocking onset are acquired by solving a nonlinear optimization problem whose objective function is constructed based on a blocking index with a triangular T21, three-level, quasi-geostrophic global spectral model. The winter climatological state is chosen as the reference basic state. Numerical results show that the optimal precursors are characterized by a baroclinic pattern with a westward tilt with height, which are mainly located upstream of the blocking region. For an optimization time of 5 days, these perturbations are mainly localized over the Northeast Atlantic Ocean and continental Europe. With the extension of the optimization time to 8 days, these perturbations are distributed more upstream and extensively in the zonal direction. Wave spectrum analysis reveals that the optimal precursors are composed of not only synoptic-scale （wave numbers 5-18） waves, but planetary-scale （wave numbers 0-4） waves as well. The synoptic-scale optimal precursors are mainly located in the mid-latitude area, while the planetary-scale optimal precursors focus primarily on the high- latitude region. The formation of a strong planetary-scale positive blocking anomaly is accompanied by the reinforcement of synoptic-scale perturbations and further fragmentation into two branches, in which the northern branch is generally stronger than the southern one. The eddy forcing arising from the selfinteraction of synoptic-scale disturbances is shown to be crucial in triggering the dipole blocking anomaly, and the planetary-scale optimal precursor provides the initial favorable background conditions for blocking onset.
基金The work was jointly supported by the Chinese Academy of Sciences （Grant No. KZCX3-SW-230） the National Natural Science Foundation of China （Grant Nos. 40233029 and 40221503）
文摘A two-layer quasi-geostrophic model is used to study the stability and sensitivity of motions on smallscale vortices in Jupiter＇s atmosphere. Conditional nonlinear optimal perturbations （CNOPs） and linear singular vectors （LSVs） are both obtained numerically and compared in this paper. The results show that CNOPs can capture the nonlinear characteristics of motions in small-scale vortices in Jupiter＇s atmosphere and show great difference from LSVs under the condition that the initial constraint condition is large or the optimization time is not very short or both. Besides, in some basic states, local CNOPs are found. The pattern of LSV is more similar to local CNOP than global CNOP in some cases. The elementary application of the method of CNOP to the Jovian atmosphere helps us to explore the stability of variousscale motions of Jupiter＇s atmosphere and to compare the stability of motions in Jupiter＇s atmosphere and Earth＇s atmosphere further.
文摘Since the last International Union of Geodesy and Geophysics General Assembly （2003）, predictability studies in China have made significant progress. For dynamic forecasts, two novel approaches of conditional nonlinear optimal perturbation and nonlinear local Lyapunov exponents were proposed to cope with the predictability problems of weather and climate, which are superior to the corresponding linear theory. A possible mechanism for the ＂spring predictability barrier＂ phenomenon for the E1 Nifio-Southern Oscillation （ENSO） was provided based on a theoretical model. To improve the forecast skill of an intermediate coupled ENSO model, a new initialization scheme was developed, and its applicability was illustrated by hindcast experiments. Using the reconstruction phase space theory and the spatio-temporal series predictive method, Chinese scientists also proposed a new approach to improve dynamical extended range （monthly） prediction and successfully applied it to the monthly-scale predictability of short-term climate variations. In statistical forecasts, it was found that the effects of sea surface temperature on precipitation in China have obvious spatial and temporal distribution features, and that summer precipitation patterns over east China are closely related to the northern atmospheric circulation. For ensemble forecasts, a new initial perturbation method was used to forecast heavy rain in Guangdong and Fujian Provinces on 8 June 1998. Additionally, the ensemble forecast approach was also used for the prediction of a tropical typhoons. A new downscaling model consisting of dynamical and statistical methods was provided to improve the prediction of the monthly mean precipitation. This new downscaling model showed a relatively higher score than the issued operational forecast.
基金Supported by the National Natural Science Foundation of China (40905023)Basic Research Program of State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences (2008LASWZI01)
文摘In this paper, a nonlinear optimization method is used to explore the finite-time instability of the atmospheric circulation with a three-level quasigeostrophic model under the framework of the conditional nonlinear optimal perturbation （CNOP）. As a natural generalization of linear singular vector （SV）, CNOP is defined as an initial perturbation that makes the cost function the maximum at a prescribed forecast time under certain physical constraint conditions. Special attentions are paid to the different structures and energy evolutions of the optimal perturbations. The results show that the most instable region of the global atmospheric circulation lies in the midlatitude Eurasian continent. More specially, SV and CNOP in the total energy norm with an optimization time of 2 days both present localness： they are mainly located in the midlatitude Asian continent and its east coast. With extension of the optimization time, SVs are more upstream and less localized in the zonal direction, and CNOPs differ essentially from SVs with broader zonal and meridional coverages; as a result, CNOPs acquire larger kinetic and available potential energy amplifications than SVs in the nonlinear model at the corresponding optimization time. For the climatological wintertime flow, it is seen that the baroclinic terms remain small over the entire time evolution, and the energy production comes essentially from the eddy kinetic energy, which is induced by the horizontal shear of the basic flow. In addition, the effects of SVs and CNOPs on the Eurasian atmospheric circulation are explored. The results show that the weather systems over the Eurasian continent in the perturbed fields by CNOPs are stronger than those by SVs at the optimization time. This reveals that the CNOP method is better in evaluating the instability of the atmospheric circulation while the SV method underestimates the possibility of extreme weather events.
基金Supported jointly by the Basic Research Project of the State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciencesthe National Natural Science Foundation of China under Grant Nos. 40633016 and 40875029
文摘Four successive freezing rain/heavy snowfall processes occurred in the southern part of China from 11 January to 2 February 2008 （named ＂0801 Southern Snow Disaster＂ hereafter）, during which a large-scale blocking circulation lasted for a long time over the mid-high latitudes of the Euro-Asian continent. This severe event is featured with a broad spatial scale, strong intensity, long duration, and serious damage. During the event, the blocking situation in the mid-high latitudes maintained quasi-sationary, but weather systems in the lower latitudes were active. Abundant water vapor was supplied, and favorable weather conditions for ice storms were formed over the large areas across the southern part of China. The results in this paper demonstrate that the significant factors responsible for the abnormal atmospheric circulation and this severe event include： 1） the very active Arctic Oscillation （AO）, which helped the permanent maintenance of the planetary-scale waves; 2） the continuous transfer of negative vorticity from the upstream region around 50°E into the blocking area, which caused the blocking situation reinforced repeatedly and sustained for a long time; and 3） the active air currents south of the Tibetan Plateau, which ensured abundant moisture supply to the southern areas of China. The 0801 Southern Snow Disaster was accompanied by extremely severe icing. In this paper, the data from Cloud-Profile Radar onboard the satellite CloudSat are used to study the dynamic and microphysical features of this event. The results show that there existed a melting layer between 2 and 4 km, and ice particles could be found above this layer and in the layer near the ground surface. Surface temperature kept between -4℃ and 0℃ with relative humidity over 90%, which provided the descending supercooled waterdrops with favorable synoptic and physical conditions to form glaze and ice at the surface via freezing, deposition and/or accretion. Causes of the event might be, as a whole, traced back to the planetary-scale systems. The study on the polar vortex anomaly in this paper reveals that changes in the polar vortex in the stratosphere preceded those in the troposphere, especially in early December 2007, while the intensification of the polar vortex in the troposphere delayed dramatically until middle January and early February of 2008. This implies that changes in the polar vortex in the stratosphere may be a precursor of the ensuing severe event and a meaningful clue for extended forecasts of such a disaster.
基金Supported by the National Natural Science Foundation of China(41230420 and 41306023)China Meteorological Administration Special Public Welfare Research Fund(GYHY201306018)
文摘This paper reviews progress in the application of conditional nonlinear optimal perturbation to targeted observation studies of the atmosphere and ocean in recent years, with a focus on the E1 Nifio-Southern Oscillation （ENSO）, Kuroshio path variations, and blocking events. Through studying the optimal precursor （OPR） and optimally growing initial error （OGE） of the occurrence of the above events, the similarity and localization features of OPR and OGE spatial structures have been found for each event. Ideal hindcasting experiments have shown that, if initial errors are reduced in the areas with the largest amplitude for the OPR and OGE for ENSO and Kuroshio path variations, the forecast skill of the model for these events is significantly improved. Due to the similarity between patterns of the OPR and OGE, additional observations implemented in the same sensitive region would help to not only capture the precursors, but also reduce the initial errors in the predictions, greatly increasing the forecast abilities. The similarity and localization of the spatial structures of the OPR and OGE during the onset of blocking events have also been investigated, but their application to targeted observation requires further study.
