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Main Energy Paths and Energy Cascade Processes of the Two Types of Persistent Heavy Rainfall Events over the Yangtze River-Huaihe River Basin


doi: 10.1007/s00376-016-6117-8

  • Two types of persistent heavy rainfall events (PHREs) over the Yangtze River-Huaihe River Basin were determined in a recent statistical study: type A, whose precipitation is mainly located to the south of the Yangtze River; and type B, whose precipitation is mainly located to the north of the river. The present study investigated these two PHRE types using a newly derived set of energy equations to show the scale interaction and main energy paths contributing to the persistence of the precipitation. The main results were as follows. The available potential energy (APE) and kinetic energy (KE) associated with both PHRE types generally increased upward in the troposphere, with the energy of the type-A PHREs stronger than that of the type-B PHREs (except for in the middle troposphere). There were two main common and universal energy paths of the two PHRE types: (2) the baroclinic energy conversion from APE to KE was the dominant energy source for the evolution of large-scale background circulations; and (3) the downscaled energy cascade processes of KE and APE were vital for sustaining the eddy flow, which directly caused the PHREs. The significant differences between the two PHRE types mainly appeared in the lower troposphere, where the baroclinic energy conversion associated with the eddy flow in type-A PHREs was from KE to APE, which reduced the intensity of the precipitation-related eddy flow; whereas, the conversion in type-B PHREs was from APE to KE, which enhanced the eddy flow.
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  • Chen S. J., L. S. Bai, and E. C. Kung, 1990: An approach to kinetic energy diagnosis of meso-synoptic scale interactions. Mon. Wea. Rev., 118, 2774- 2780.http://xueshu.baidu.com/s?wd=paperuri%3A%2801584c1a760ec7901be0b374fc451ace%29&filter=sc_long_sign&tn=SE_xueshusource_2kduw22v&sc_vurl=http%3A%2F%2Fadsabs.harvard.edu%2Fcgi-bin%2Fnph-data_query%3Fbibcode%3D1990MWRv..118.2774C%26db_key%3DPHY%26link_type%3DABSTRACT&ie=utf-8&sc_us=2867226730803854591
    Ding Y. H., 1993: Study of Strong Heavy Rianfall in Yangtze-Huai River in 1991. China Meteorological Press, Beijing, 1- 255. (in Chinese)
    Fu S. M., J. H. Sun, S. X. Zhao, and W. L. Li, 2011: The energy budget of a southwest vortex with heavy rainfall over South China. Adv. Atmos. Sci.,28(4), 709-724, doi: 10.1007/ s00376-010-0026-z.http://d.wanfangdata.com.cn/Periodical_dqkxjz-e201103020.aspx
    Fu S. M., F. Yu, D. H. Wang, and R. D. Xia, 2013: A comparison of two kinds of eastward-moving mesoscale vortices during the mei-yu period of 2010. Science China Earth Sciences, 56, 282- 300.http://www.cnki.com.cn/Article/CJFDTotal-JDXG201302011.htm
    Fu S. M., W. L. Li, and J. Ling, 2015: On the evolution of a long-lived mesoscale vortex over the Yangtze River Basin: Geometric features and interactions among systems of different scales. J. Geophys. Res. Atmos.,120, 11 889-11 917, doi: 10.1002/2015JD023700.http://onlinelibrary.wiley.com/doi/10.1002/2015JD023700/pdf
    Fu S. M., J. H. Sun, J. Ling, H. J. Wang, and Y. C. Zhang, 2016: Scale interactions in sustaining persistent torrential rainfall events during the Mei-yu season. J. Geophys. Res. Atmos.,121, doi: 10.1002/2016JD025446.http://www.researchgate.net/publication/309241488_Scale_interactions_in_sustaining_persistent_torrential_rainfall_events_during_the_Mei-yu_season
    Guo S. L., F. Ge, R. Ma, L. Tian, and L. Zhou, 2012: Analysis of the accumulation and propagation of wave packets during a heavy rainfall process in southern China. Journal of Tropical Meteorology, 28( 5), 585- 593 (in Chinese).http://en.cnki.com.cn/Article_en/CJFDTOTAL-RDQX201204019.htm
    Holopainen E. O., 1978: A diagnostic study on the kinetic energy balance of the long-term mean flow and the associated transient fluctuation in the atmosphere. Geophysica, 15, 125- 145.
    Li T. T., X. F. Li, 2016: Barotropic processes associated with the development of the Mei-yu precipitation system. Adv. Atmos. Sci.,33(5), 593-598, doi:10.1007/s00376-015-5146-z.http://d.wanfangdata.com.cn/Periodical/dqkxjz-e201605006
    Li Y. F., 2007: Conversion of kinetic energy from synoptic scale disturbance to low-frequency fluctuation over the Yangtze River valley in the summers of 1997 and 1999. Adv. Atmos. Sci.,24(5), 591-598, doi: 10.1007/s00376-007-0591-y.http://d.wanfangdata.com.cn/Periodical_dqkxjz-e200704005.aspx
    Murakami S., 2011: Atmospheric local energetics and energy interactions between mean and eddy fields. Part I: Theory. J. Atmos. Sci., 68, 760- 768.http://adsabs.harvard.edu/abs/2011JAtS...68..760M
    Murakami S., R. Ohgaito, and A. Abe-Ouchi, 2011: Atmospheric local energetics and energy interactions between mean and eddy fields. Part II: An example for the Last Glacial Maximum climate. J. Atmos. Sci., 68, 533- 552.http://adsabs.harvard.edu/abs/2011JAtS...68..533M
    Plumb R. A., 1983: A new look at the energy cycle. J. Atmos. Sci., 40, 1669- 1688.http://adsabs.harvard.edu/abs/1983JAtS...40.1669P
    Ritchie E. A., G. J. Holland, 1997: Scale interactions during the formation of Typhoon Irving. Mon. Wea. Rev., 125, 1377- 1396.http://adsabs.harvard.edu/abs/1997MWRv..125.1377R
    Saha, S., Coauthors, 2010: The NCEP climate forecast system reanalysis. Bull. Amer. Meteor. Soc.,91, 1015-1057, doi: 10.1175/2010BAMS 3001.1.http://www.cabdirect.org/abstracts/20103296323.html
    Tang Y. B., J. J. Gan, L. Zhao, and K. Gao, 2006: On the climatology of persistent heavy rainfall events in China. Adv. Atmos. Sci.,23(5), 678-692, doi: 10.1007/s00376-006-0678-x.http://d.wanfangdata.com.cn/Periodical_dqkxjz-e200605003.aspx
    Tao S. Y., 1980: Heavy Rainfall Events in China. Science Press, Beijing, 45- 46 (in Chinese).
    Tao S. Y., S. Xu, 1962: Some aspects of the circulation during the periods of the persistfnt drought and flood in Yantze and Hwai-ho valleys in summer. Acta Meteorologica Sinica, 32( 2), 1- 10 (in Chinese).http://en.cnki.com.cn/Article_en/CJFDTOTAL-QXXB196201000.htm
    Tao S. Y., Y. Q. Ni, S. X. Zhao, S. J. Chen, and J. J. Wang, 2001: The Study on Formation Mechanism and Forecasting of Heavy Rainfall in the Summer 1998. China Meteorological Press, 183- 184 (in Chinese).
    Tao S. Y., X. L. Zhang, and S. L. Zhang, 2004: A Study on the Disaster of Heavy Rainfalls over the Yangtze River Basin in the Meiyu Period. China Meteorological Press,192 pp (in Chinese).
    Wang H. J., J. H. Sun, J. Wei, and S. X. Zhao, 2014: Classification of persistent heavy rainfall events over southern China during recent 30 years. Climatic and Environmental Research, 19( 6), 713- 725 (in Chinese).http://en.cnki.com.cn/Article_en/CJFDTotal-QHYH201406006.htm
    Xu Y. F., 2008: The spatial-temporal variation of persistent heavy rainfall in south of China in summer and its corresponding general circulation feature. M. S. thesis, Nanjing University of Science and Technology, 8- 46 (in Chinese).
    Zhao S. X., Z. Y. Tao, J. H. Sun, and N. F. Bei, 2004: Study on Mechanism of Formation and Development of Heavy Rainfalls on Meiyu front in Yangtze River. China Meteorological Press,282 pp (in Chinese).
  • [1] Jing YANG, Sicheng HE, Qing BAO, 2021: Convective/Large-scale Rainfall Partitions of Tropical Heavy Precipitation in CMIP6 Atmospheric Models, ADVANCES IN ATMOSPHERIC SCIENCES, 38, 1020-1027.  doi: 10.1007/s00376-021-0238-4
    [2] SU Qin, LU Riyu, LI Chaofan, 2014: Large-scale Circulation Anomalies Associated with Interannual Variation in Monthly Rainfall over South China from May to August, ADVANCES IN ATMOSPHERIC SCIENCES, 31, 273-282.  doi: 10.1007/s00376-013-3051-x
    [3] Yating ZHAO, Ming XUE, Jing JIANG, Xiao-Ming HU, Anning HUANG, 2024: Assessment of Wet Season Precipitation in the Central United States by the Regional Climate Simulation of the WRFG Member in NARCCAP and Its Relationship with Large-Scale Circulation Biases, ADVANCES IN ATMOSPHERIC SCIENCES, 41, 619-638.  doi: 10.1007/s00376-023-2353-x
    [4] Jong-Kil PARK, LU Riyu, LI Chaofan, Eun Byul KIM, 2012: Interannual Variation of Tropical Night Frequency in Beijing and Associated Large-Scale Circulation Background, ADVANCES IN ATMOSPHERIC SCIENCES, 29, 295-306.  doi: 10.1007/s00376-011-1141-1
    [5] Lei YIN, Fan PING, Jiahua MAO, Shuanggen JIN, 2023: Analysis on Precipitation Efficiency of the “21.7” Henan Extremely Heavy Rainfall Event, ADVANCES IN ATMOSPHERIC SCIENCES, 40, 374-392.  doi: 10.1007/s00376-022-2054-x
    [6] ZHANG Meng, NI Yunqi, ZHANG Fuqing, 2007: Variational Assimilation of GPS Precipitable Water Vapor and Hourly Rainfall Observations for a Meso- Scale Heavy Precipitation Event During the 2002 Mei-Yu Season, ADVANCES IN ATMOSPHERIC SCIENCES, 24, 509-526.  doi: 10.1007/s00376-007-0509-8
    [7] Gong-Wang Si, Kuranoshin Kato, Takao Takeda, 1995: The Early Summer Seasonal Change of Large-scale Circulation over East Asia and Its Relation to Change of The Frontal Features and Frontal Rainfall Environment During 1991 Summer, ADVANCES IN ATMOSPHERIC SCIENCES, 12, 151-176.  doi: 10.1007/BF02656829
    [8] Huijie WANG, Jianhua SUN, Shenming FU, Yuanchun ZHANG, 2021: Typical Circulation Patterns and Associated Mechanisms for Persistent Heavy Rainfall Events over Yangtze–Huaihe River Valley during 1981–2020, ADVANCES IN ATMOSPHERIC SCIENCES, 38, 2167-2182.  doi: 10.1007/s00376-021-1194-8
    [9] YU Ye, Xiaoming CAI, QIE Xiushu, 2007: Influence of Topography and Large-scale Forcing on the Occurrence of Katabatic Flow Jumps in Antarctica: Idealized Simulations, ADVANCES IN ATMOSPHERIC SCIENCES, 24, 819-832.  doi: 10.1007/s00376-007-0819-x
    [10] Luo Dehai, 1999: Nonlinear Three-Wave Interaction among Barotropic Rossby Waves in a Large-scale Forced Barotropic Flow, ADVANCES IN ATMOSPHERIC SCIENCES, 16, 451-466.  doi: 10.1007/s00376-999-0023-2
    [11] Yuhan LUO, Yu DU, 2023: The Roles of Low-level Jets in “21·7” Henan Extremely Persistent Heavy Rainfall Event, ADVANCES IN ATMOSPHERIC SCIENCES, 40, 350-373.  doi: 10.1007/s00376-022-2026-1
    [12] K. D. Prasad, S. V. Singh, 1988: LARGE-SCALE FEATURES OF THE INDIAN SUMMER MON-SOON RAINFALL AND THEIR ASSOCIATION WITH SOME OCEANIC AND ATMOSPHERIC VARIABLES, ADVANCES IN ATMOSPHERIC SCIENCES, 5, 499-513.  doi: 10.1007/BF02656794
    [13] FAN Lijun, XIONG Zhe, 2015: Using Quantile Regression to Detect Relationships between Large-scale Predictors and Local Precipitation over Northern China, ADVANCES IN ATMOSPHERIC SCIENCES, 32, 541-552.  doi: 10.1007/s00376-014-4058-7
    [14] Maeng-Ki KIM, Yeon-Hee KIM, 2010: Seasonal Prediction of Monthly Precipitation in China Using Large-Scale Climate Indices, ADVANCES IN ATMOSPHERIC SCIENCES, 27, 47-59.  doi: 10.1007/s00376-009-8014-x
    [15] WANG Yi, YAN Zhongwei, 2011: Changes of Frequency of Summer Precipitation Extremes over the Yangtze River in Association with Large-scale Oceanic-atmospheric Conditions, ADVANCES IN ATMOSPHERIC SCIENCES, 28, 1118-1128.  doi: 10.1007/s00376-010-0128-7
    [16] CHU Kekuan, TAN Zhemin, Ming XUE, 2007: Impact of 4DVAR Assimilation of Rainfall Data on the Simulation of Mesoscale Precipitation Systems in a Mei-yu Heavy Rainfall Event, ADVANCES IN ATMOSPHERIC SCIENCES, 24, 281-300.  doi: 10.1007/s00376-007-0281-9
    [17] Yang Fanglin, 1991: The Stability of Large-Scale Horizontal Air Motion in the Non-linear Basic Zephyr Flow under the Effect of Rossby Parameter, ADVANCES IN ATMOSPHERIC SCIENCES, 8, 149-164.  doi: 10.1007/BF02658091
    [18] LI Xiaofan, SHEN Xinyong, LIU Jia, 2014: Effects of Doubled Carbon Dioxide on Rainfall Responses to Large-Scale Forcing: A Two-Dimensional Cloud-Resolving Modeling Study, ADVANCES IN ATMOSPHERIC SCIENCES, 31, 525-531.  doi: 10.1007/s00376-013-3030-2
    [19] Kelvin S. NG, Gregor C. LECKEBUSCH, Kevin I. HODGES, 2022: A Causality-guided Statistical Approach for Modeling Extreme Mei-yu Rainfall Based on Known Large-scale Modes—A Pilot Study, ADVANCES IN ATMOSPHERIC SCIENCES, 39, 1925-1940.  doi: 10.1007/s00376-022-1348-3
    [20] TANG Yanbing, GAN Jingjing, ZHAO Lu, GAO Kun, 2006: On the Climatology of Persistent Heavy Rainfall Events in China, ADVANCES IN ATMOSPHERIC SCIENCES, 23, 678-692.  doi: 10.1007/s00376-006-0678-x

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Manuscript received: 22 April 2016
Manuscript revised: 20 August 2016
Manuscript accepted: 26 September 2016
通讯作者: 陈斌, bchen63@163.com
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Main Energy Paths and Energy Cascade Processes of the Two Types of Persistent Heavy Rainfall Events over the Yangtze River-Huaihe River Basin

  • 1. Key Laboratory of Cloud-Precipitation Physics and Severe Storms, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 2. University of Chinese Academy of Sciences, Beijing 100049, China
  • 3. International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Abstract: Two types of persistent heavy rainfall events (PHREs) over the Yangtze River-Huaihe River Basin were determined in a recent statistical study: type A, whose precipitation is mainly located to the south of the Yangtze River; and type B, whose precipitation is mainly located to the north of the river. The present study investigated these two PHRE types using a newly derived set of energy equations to show the scale interaction and main energy paths contributing to the persistence of the precipitation. The main results were as follows. The available potential energy (APE) and kinetic energy (KE) associated with both PHRE types generally increased upward in the troposphere, with the energy of the type-A PHREs stronger than that of the type-B PHREs (except for in the middle troposphere). There were two main common and universal energy paths of the two PHRE types: (2) the baroclinic energy conversion from APE to KE was the dominant energy source for the evolution of large-scale background circulations; and (3) the downscaled energy cascade processes of KE and APE were vital for sustaining the eddy flow, which directly caused the PHREs. The significant differences between the two PHRE types mainly appeared in the lower troposphere, where the baroclinic energy conversion associated with the eddy flow in type-A PHREs was from KE to APE, which reduced the intensity of the precipitation-related eddy flow; whereas, the conversion in type-B PHREs was from APE to KE, which enhanced the eddy flow.

1. Introduction
  • The Yangtze River-Huaihe River valleys often suffer persistent heavy rainfall events (PHREs) in the warm season. The related severe flooding events cause large economic, life, and property losses, such as the well-known Yangtze River flood events in 1998 and 1999 (Tao et al., 2001, 2004, Zhao et al., 2004), and the notable Huaihe River flood events in 1991, 2003 and 2007 (Ding, 1993; Zhao et al., 2004). Previous studies have found that large-scale circulation stability is essential for the persistence of heavy precipitation (Tao and Xu, 1962), and thus they proposed that a proper classification of the large-scale circulation patterns is vital for forecasting and understanding PHREs. Previous studies have classified PHREs into different types according to different motivations. For instance, (Tang et al., 2006) pointed out that the PHREs they selected could be classified into five categories according to their intensity, into three types according to their circulation regime, and into eight groups according to the geographic locations of their rainbands. (Xu, 2008) applied EOF analysis to divide the PHREs in South China into three modes: consistent, transmeridional alternate, and latitudinal opposition. Most recently, (Wang et al., 2014) utilized daily precipitation data from 752 stations in China to classify the PHREs over South China. Using the objective pattern correlation method, they classified PHREs in the Yangtze River-Huaihe Rriver valley into three basic types: type A, with the main rainbelt located to the south of the Yangtze River; type B, with the main rainbelt located to the north of the Yangtze River; and type C, with the main rainbelt stretched along the Yangtze River. Based on this classification system, a composite study was conducted to show the main similarities and differences among the three PHRE types.

    The mechanisms accounting for the persistence of precipitation is a critical topic. Energetics, including the available potential energy (APE) and kinetic energy (KE), has been effectively employed in PHRE-related studies (Fu et al., 2011, 2013; Guo et al., 2012). Of these, some studies have tried to clarify the energy conversion between the precipitation-related eddy flow and its background circulation (mean flow). For instance, (Chen et al., 1990) used horizontal filtering to diagnose the scale interaction that transferred KE from synoptic-scale systems to mesoscale systems. (Ritchie and Holland, 1997) proposed that scale interactions of energy resulted in favorable conditions for storm development. (Li, 2007) showed that the energy conversion from a synoptic scale disturbance to the low-frequency fluctuation was obviously enhanced in the middle and lower troposphere during the heavy rainfall. (Fu et al., 2015) analyzed a long-lived mesoscale vortex and found that the downscaled energy cascade process (ECP) of KE was the key factor for sustaining this heavy precipitation vortex. (Li and Li, 2016) found that the energy conversion between the eddy flow and its background circulation contributed to the development of the precipitation systems during a heavy rainfall event.

    As mentioned above, although previous studies have shown that the scale interactions of energy can affect a heavy rainfall event significantly, the specific mechanisms underlying the interactions between the precipitation-related eddy flow and its background circulation have rarely been discussed. Moreover, for PHREs over the Yangtze River-Huaihe River valleys, the mechanisms dominating their persistence and the main energy paths of different scale weather systems remain unclear. Therefore, based on the classification of PHREs from (Wang et al., 2014), this study was conducted to address these two points.

    The paper is structured as follows. The data and methodology are introduced in section 2. Section 3 provides an overview of the selected PHREs. A comparison of the energy features and paths of the PHRE types are summarized in section 4. Finally, a conclusion and discussion is provided in section 5.

2. Data and methodology
  • Six-hourly NCEP CFSR data (0.5°× 0.5°) (Saha et al., 2010) were used for the synoptic analysis and energy calculations in this study. Using daily precipitation data from 752 meteorological stations in China (interpolated into 0.25°× 0.25° grids based on the Cressman objective method), (Wang et al., 2014) classified the PHREs over the Yangtze River-Huaihe Rriver basin into three basic types: type A (main rainbelt located south of the Yangtze River); type B (main rainbelt located north of the Yangtze River); and type C (main rainbelt located along the Yangtze River). Of these three types, type A and type B show significant differences in their precipitation distribution, circulation patterns and influencing systems, while type C mainly shows hybrid features of type A and type B. Moreover, type A and type B show a more stable maintenance state than type C. Therefore, the present study primarily focused on types A and B; the features of type-C PHREs are presented in the conclusion and discussion (section 5). The former two types were compared in detail to understand the fundamental energy characteristics governing the PHREs over the Yangtze River-Huaihe River basin.

  • According to the Fourier series, a meteorological variable can be decomposed into a mean part and a perturbation part, i.e., \(b=\bar{b}+b'\), where b is a sample variable, the overbar represents a time-mean operator (mean or running mean), and the prime represents a perturbation operator. The perturbation part is the direct trigger for a PHRE, and the mean part acts as the background for the variation of the perturbation. As APE and KE are key factors during a PHRE (Fu et al., 2013), they were analyzed in detail to determine the respective fundamental mechanisms sustaining the type-A and type-B PHREs. Eight PHRE cases persisting for about three days (four cases of each type) were selected to study the energy characteristics of type-A and -B PHREs. Because all eight PHRE cases persisted for approximately three days [Table 1; these cases are also shown in Table 5 of (Wang et al., 2014)], a time window of 72 h was used to conduct the temporal scale separation (calculating the mean or running mean). After separation, the flow was decomposed into a perturbation part (eddy flow) with the period below 72 h, and its background circulation (mean flow). Then, the interaction between the precipitation-related eddy flow and its background circulation was investigated using the energy diagnostic scheme from (Murakami, 2011): \begin{eqnarray} \label{eq1} \partial A_{\rm M}/\partial t&=&G(A_{\rm M})-C(A_{\rm M},K_{\rm M})-C(A_{\rm M},A_{\rm I})-B(A_{\rm M})+R(A_{\rm M}) ,(1)\\ \label{eq2} \partial K_{\rm M}/\partial t&=&C(A_{\rm M},K_{\rm M})-C(K_{\rm M},K_{\rm I})-D(K_{\rm M})-B(K_{\rm M}) ,(2)\quad\\ \label{eq3} \partial\overline {A_{\rm T}}/\partial t&=&G(\overline {A_{\rm T}})-C(\overline {A_{\rm T}},\overline {K_{\rm T}})-C(\overline {A_{\rm T}},A_{\rm I}) -B(\overline {A_{\rm T}}),(3)\\ \label{eq4} \partial\overline {K_{\rm T}}/\partial t&=&C(\overline {A_{\rm T}},\overline {K_{\rm T}})-C(\overline {K_{\rm T}},K_{\rm I}) -D(\overline {K_{\rm T}})-B(\overline {K_{\rm T}}).(4) \end{eqnarray} Here, A M, A I and A T are the time-mean, interaction and perturbation APE, respectively; and K M, K I and K T are the time-mean, interaction and perturbation KE, respectively. The terms G(A M) and \(G(\overline{A_\rm T})\) are the diabatic generation or extinction of A M and A T. C(X1,X2) represents the conversion between the energy X1 and energy X2. D(K M) and \(D(\overline {K_\rm T})\) denote the dissipation of K M and K T. B(X) is the three- dimensional transport associated with X. R(A M) represents the vertical transport of heat. Unlike traditional energy budget systems (Holopainen, 1978; Plumb, 1983), the energy budget used in this study has an interaction APE term (A I) and an interaction KE term (K I). These two new types of energy act as a linkage between the mean energy and perturbation energy, which remove the ambiguity associated with the energy conversion in traditional local energy diagnostic schemes (Holopainen, 1978; Plumb, 1983). For details of the energy budget system used in this study, please refer to (Murakami et al., 2011), (Murakami et al., 2011) and (Fu et al., 2016).

3. Overview of the PHREs
  • A total of eight PHREs were selected in this study——four type A cases and four type B cases (Table 1), all of which lasted for three days. These events all appeared between June and July, and most of them occurred during the typical mei-yu period (15 June-15 July). The three-day averaged 850 hPa perturbation KE and the corresponding three-day accumulated precipitation are shown in Fig. 1. The location, orientation and distribution of the accumulated precipitation were highly consistent with the perturbation KE, which implies the perturbation was the direct trigger for the PHREs and the perturbation KE can be used as an effective indicator for the precipitation-related eddy flow. To show the overall feature of the precipitation-related eddy flow, an area mean was calculated. Following the definition of the key region (green box in Fig. 2) in (Wang et al., 2014), the energy budget terms of the type-A PHREs were averaged within the south box (south of the Yangtze River) [(26°-30°N, 112°-122.5°E); key area for type A (KA-A); Fig. 3], and those of the type-B PHREs were averaged within the north box [(30°-34°N, 112°-122.5°E); key area for type B (KA-B); Fig. 3].

    Figure 1.  The three-day total precipitation (color shading; units: mm) and the three-day time-averaged perturbation KE (blue contours; units: m-2 s-2) of the three types of PHREs. The left (right) column is for the four type-A (type-B) events.

    Figure 2.  Three-day averaged geopotential height (black contours; units: gpm) and temperature (red contours; units: K) at 500 hPa for type-A (left) and type-B (right) case. The green boxes in the figures symbolize our study area.

    Figure 3.  Three-day averaged wind fields (blue wind barbs) and vorticity (>0; color shading; units: 10-5 s-1) at 850 hPa for type-A (left column) and type-B (right column) case. The purple boxes in the figures are the study areas. The grey shading represents the terrain higher than 1500 m.

  • Generally, during each of the eight selected PHREs, the background circulation maintained quasi-stationarity (not shown). This provided favorable conditions for the sustainment of the PHREs. Figure 2 shows the 3-day averaged geopotential height and temperature at 850 hPa of each case. For type A (left column in Figs. 2 and 3), though the circulation at high latitude varied among the four cases, a low trough covered East China and the key area was located in the regions from the rear to the base of this trough. The northwesterlies behind the trough and the southwesterlies along the northwestern edge of the western Pacific subtropical high (WPSH) converged over KA-A, corresponding with the stronger positive vorticity at 850 hPa (Fig. 3, left column). However, the circulation distribution of the cases in 1989 and 2000 showed larger meridional amplitudes at 500 hPa and stronger convergence at 850 hPa than the other two cases. For type B (right column in Figs. 2 and 3), the WPSH landed to the areas south of the Yangtze River and weak ridges covered the mid-high latitudes. The circulation distribution featured small meridional amplitudes. KA-B in the four cases was ahead of the ridges (Fig. 2), with the convergence belt situated north of the Yangtze River.

  • To show the respective common features for the type-A and -B PHREs' background circulations, separate composites for the four type-A and four type-B cases were produced (Figs. 4 and 5). For the type-A PHREs, the geopotential height at 200 hPa showed a typical two trough and one ridge pattern in the middle to high latitudes (Fig. 4a): the western low trough was located over Lake Balkhash, the eastern trough extended from North China to the lower reaches of the Yangtze River, and the ridge in the middle covered the region south of Lake Baikal. The South Asia high dominated the whole of the low latitudes. KA-A was beneath the south part of the western trough and the northeastern part of the South Asia high. The upper-level jets mainly persisted between 30°N and 45°N. For the type-B PHREs, the 200 hPa circulation was obviously flatter than that in type A, with a straight westerly flow persisting in the middle and high latitudes and a weak ridge located at approximately 110°E, covering North China. The upper-level jets covered the area between 35°N and 45°N, which was to the north of the 200 hPa jet in the type-A PHREs. The South Asia high was stronger and wider than in the type-A PHREs, and extended northward to approximately 30°N. KA-A was located in the northeast quadrant of the South Asia high (Fig. 4b). The 500 hPa geopotential height in the type-A and -B PHREs in the middle to high latitudes showed a similar pattern to that at 200 hPa. KA-A was governed by the northwesterly wind, and the 5880 gpm isohypse of the WPSH covered the area east of 120°E and south of 30°N. The westerly wind governed KA-B PHREs and the subtropical high covered KA-B. At lower levels, the northeast-southwest oriented convergence belt in the type-A PHREs was located south of the Yangtze River, corresponding to a potential temperature trough with a strong temperature gradient (Figs. 5a and c), which meant that the baroclinicity was strong. In contrast, the convergence belt of the type-B PHREs was mainly orientated in the west-east direction and extended north of the Yangtze River. It was weaker than that in the type-A PHREs, and located at the north edge of the high potential temperature region (Figs. 5b and d).

    Figure 4.  (a, b) Composite averaged geopotential height (black contours; units: gpm) and jets (wind speed >30 m s-1; blue wind barbs) at 200 hPa: (a) the four type-A PHREs; (b) the four type-B PHREs. (c, d) Averaged geopotential height (black contours; units: gpm) and temperature (red contours; units: K) at 500 hPa: (c) the four type-A PHREs; (d) the four type B PHREs. The green rectangles are the key areas [northern side is the key area for type A (KA-A); southern side is the key area for type B (KA-B)] in this study.

    Figure 5.  (a, b) Composite averaged potential temperature (red contours; units: K) and divergence (<0; color shading; units: 10-5 s-1) at 850 hPa: (a) the four type-A PHREs; (b) the four type-B PHREs. (c, d) Averaged wind fields (blue wind barbs) and vorticity (>0; color shading; units: 10-5 s-1) at 850 hPa: (c) the four type-A PHREs; (d) the four type-B PHREs. The purple rectangles are the key areas [northern side is key area for type A (KA-A); southern side is key area for type B (KA-B)] in this study. The grey shading indicates terrain height >1500 m.

4. Energy features of the two types of PHREs
  • As shown in Fig. 1 and Figs. 5c and d, in both of the four-case composites for the type-A and -B PHREs, the lower-level three-day averaged K T band corresponded closely to the convergence and cyclonic vorticity band (low-level wind shear or mei-yu front). This confirms that the stably persistent perturbation KE band acted as a direct trigger for the selected PHREs. Therefore, a thorough analysis of how this strong perturbation KE band was maintained could explain how the PHREs were sustained. The energy diagnostic scheme derived by (Murakami, 2011) was used to calculate the related energy characteristics (section 2.2).

    To show the overall feature, the energy budget terms of Eqs. (2)-(5) were first averaged within the north box of the key area [KA-A; (26°-30°N, 112°-122.5°E)] for type-A PHREs, and within the south box [KA-B; (30°-34°N, 112°-122.5°E)] for type-B PHREs. Then, the horizontally averaged values were integrated vertically. The vertical integrals were calculated among three equal layers and the total layers. For the lower levels, the budget terms were integrated from 950 hPa to 700 hPa (950 hPa was used as the bottom level to avoid including information beneath the topography), the middle levels were integrated between 650 and 400 hPa, and the upper levels from 350 hPa to 100 hPa. The integration of the total levels started from 950 hPa and ended at 100 hPa.

  • Integrated energy values during the three-day persistent precipitation period are shown in Fig. 6. To reflect the relative importance of the perturbation (precipitation-related eddy flow) regarding the mean state (mean flow and background circulation), a ratio of K T (A T) divided by the sum of K T (A T) and K M (A M) was calculated, and was defined as the relative perturbation for KE (APE).

    For the energy of the background circulation, the K M maxima of the eight PHREs all appeared in the upper levels and decreased downward, which corresponded to the vertical configuration of the background circulation (Figs. 4 and 5). Generally, the K M in the upper and middle levels of the four type-A events was larger than that in the four type-B events, whereas the K M in the lower levels of the two types of PHREs showed little obvious difference. The A M maximum of each PHRE also mainly appeared in the upper levels (except for the event in 1994), with the A M values in the middle levels being slightly smaller than those in the upper levels. Similar to the differences in K M between the type-A and -B PHREs, the A M in the upper and middle levels was larger for the type-A PHREs, whereas the A M in the lower levels was almost the same for the two types of PHREs. No obvious differences in the lower-level A M and K M between the type-A and type-B PHREs meant that the background circulations in the lower troposphere resembled each other, and provided favorable conditions for sustaining the precipitation-related eddy flow, which was mainly located in the lower troposphere (Fu et al., 2015).

    For the perturbation energy, it was clear that, in all four layers, the relative perturbation of KE was generally larger for the type-B PHREs. This meant that the precipitation-related eddy flow in the type-B PHREs had stronger relative intensity. In contrast to the vertical distribution of K M, the relative perturbation of KE reached a maximum in the lower levels and a minimum in the middle levels. The appearance of maximum relative perturbation of KE in the lower levels meant, dynamically, the precipitation was mainly triggered by lower-tropospheric systems. The relative perturbation of APE in all eight PHREs also peaked in the lower levels, which indicated that the maximum relative perturbation in the thermodynamical fields also appeared in the lower troposphere. The relative perturbation of APE was larger for type-B PHREs in the middle and upper levels, whereas the opposite was true for the lower levels.

    Figure 6.  The vertical integral of the key areas' averaged mean KE (KM), mean APE (AM), the relative perturbation KE (KT) and perturbation APE (AT). Red circles, triangles and squares are for the energy integrated for the upper levels (UL), middle levels (ML) and lower levels (LL) of type-A PHREs, and those with blue color are for the energy of type-B PHREs.

    Figure 7.  Vertical integral of the area-averaged (26°-34°N, 122°-122.5°E) energy (units: J m-2) and budget terms (units: W m-2) at the different levels for type-A PHREs. A M, A I and A T are the time-mean, interaction and perturbation APE; and K M, K I and K T are the time-mean, interaction and perturbation KE. G(A M) and G(A T) are the diabatic generation or extinction of A M and A T. C(X1,X2) represents the conversion between the energy X1 and energy X2. D(A M) and D(A T) denote the dissipation of K M and K T. B(X) is the three-dimensional transport associated with X. R(A M) represents the vertical transport of heat.

  • The energy features in the total levels were investigated to show the overall energy characteristics of the precipitation region, and the energy features in the lower levels were analyzed in detail as they were directly linked to the PHREs (Fig. 7). In the total levels, for the four type-A PHREs, the main energy paths of the background circulation were as follows. The baroclinic energy conversion (BCEC) from A M to K M dominated the maintenance of K M. The transport effect B(A M) was the main factor favorable for the maintenance of A M. The diabatic effect G(A M) and the vertical heat transport effect R(A M) also contributed to the persistence of A M. For the eddy flow, G(A T) was dominant for the energy maintenance of A T. A T was produced by heating in warm regions or cooling in cold regions, while heating in cold regions or cooling in warm regions had the opposite effect. A T was reduced by the BCEC of the eddy flow [i.e., C(A T,K T)>0]. Meanwhile, the BCEC was the main energy source for the sustainment of K T. Within the precipitation region, a proportion of K T was converted into K I (except for the 2000 PHRE). The eddy transport B(K T) and the friction effect D(K T) also consumed K T. A small part of A M was transferred to A I and then A I was converted into A T, which meant a downscaled ECP of APE appeared. This downscaled ECP of APE was the second dominant factor for maintaining A T. A I was primarily produced by interactions with the background circulation. K I in the 1994 and 1998 PHREs was mainly generated by interactions with the eddy flow and background circulation, whereas the K I of the 1989 PHRE received energy from K T and converted the energy to K M, i.e., an upscaled ECP, indicating KE was transferred from the eddy flow to its background circulation. In contrast, K I in the 2000 case was mainly generated from interactions with the background circulation.

    The energy paths in the upper levels (350 to 100 hPa, not shown) of the four events was similar to the corresponding path in the total levels. B(A M), G(A M) and R(A M) also contributed to the maintenance of A M, with the BCEC process from A M to K M dominating the persistence of K M. The downscaled ECP of APE appeared in three events (except for the PHRE in 1998), which was important for sustaining A T, whereas the BCEC process converted a part of A T to K T, which reduced A T. K I was mainly generated through interactions with the eddy flow and background circulation (except for the 1989 event). The energy source of A M and the BCEC processes from APE to KE (both background circulation and eddy flow) in the middle levels (650 to 400 hPa) were the same as those in the total levels. Unlike the significant downscaled ECP of APE in the total and upper levels, there was no obvious ECP in the middle levels. Both A M and A T converted the energy to A I and then most of A I was transported out of KA-A by the eddy flow [F(A I)>0]. Both the background circulation and eddy flow converted KE to K I through C(K M,K I) and C(K T,K I), respectively, in the PHREs of 1994 and 2000. For the PHREs of 1989 and 1998, an upscaled ECP, which transferred KE from the eddy flow to the background circulation, appeared, but it was negligible to the evolution of K M.

    Previous studies have demonstrated that, over the Yangtze River-Huaihe River valleys, the precipitation-related eddy flow is primarily maintained in the lower levels (950-700 hPa) (Tao, 1980; Zhao et al., 2004). The results of the present study confirm this result (maximum relative perturbation of APE and KE both appeared in the lower levels). Therefore, the energy paths in the lower levels could indicate the energy evolution of weather systems that are directly related to rainfall. In the lower levels, the energy paths and cascade processes were generally similar for the four PHREs. The similarities are summarized as follows. First, the diabatic effect G(A M) and the vertical heat transport effect R(A M) were both favorable for A M persistence. Second, the BCEC from A M to K M was dominant for the maintenance of K M, whereas the transport effects B(K M) and D(K M) were the main consumption factors for reducing K M. Third, except for the PHRE in 2000, the BCEC of the eddy flow was from KE to APE, reducing the intensity of the eddy flow. This was the most significant difference in the energy path compared with other levels. Finally, remarkable downscaled ECPs of APE and KE appeared in the lower troposphere, showing that the background circulation acted as a crucial energy source for the precipitation-related eddy flow.

  • The energy paths in the total levels of the type-B PHREs showed obvious similarities to the type-A PHREs (Fig. 8). First, for the background circulation, B(A M), G(A M) and R(A M) were favorable for the maintenance of A M, with B(A M) acting as the dominant energy source. The BCEC from A M to K M was the main KE source for the background circulation. For the eddy flow, G(A T) mainly produced A T (except for the 2002 PHRE). The BCEC of eddy flow converted energy from APE to KE, which dominated the persistence of K T. The primary energy source of A I was the interaction with the background circulation, and A I was mainly converted into A T, which was a downscaled ECP of APE. The downscaled ECP of KE only appeared in the PHREs of 1996 and 2002; whereas, in the other two PHREs, the generation of K I was primarily from the interactions with both the eddy flow and the background circulation.

    The energy path in the upper levels (not shown) was similar to that in the total levels. The transport effect B(A M) and the diabatic effect G(A M) were mainly conducive to the sustainment of A M. The BCEC from A M(A T) to K M(K T) was the unique dominant energy source of background (eddy flow) KE. For the interaction energy, downscaled ECPs only appeared in the thermodynamical fields (APE). In contrast, both the background circulation and eddy flow transferred KE to K I through C(K M,K I) and C(K T,K I), respectively (except for the 2007 PHRE). The BCEC of the background circulation and eddy flow in the middle levels were the same as those in the total levels; however, the ECPs of APE and KE were different (not shown). For the ECPs of KE, an upscaled ECP (energy conversion from K T to K M through K I) appeared in the 1991 and 2007 PHREs.

    For the energy paths and ECPs in the lower levels of the four type-B events, the main similarities can be summarized as follows (Fig. 8). First, G(A M) and R(A M) were favorable for the maintenance of A M. The BCEC from APE to KE of the background circulation [C(A M,K M)>0] was the unique dominant energy source for the sustainment of K M. The second common feature was that the BCEC from A T to K T, favorable for the development of the precipitation-related weather systems, appeared (except for the PHRE of 1996). Third, downscaled ECPs appeared both in APE and KE. The background circulation transferred energy (APE and KE) into the precipitation-related eddy flow through the interaction energy.

  • The differences and similarities between the two types of PHREs are discussed in this section. As described in section 3.1, comparison of the KE and APE associated with the background circulation showed that the type-A PHREs (rainbelt located south of the Yangtze River) were generally stronger than the type-B PHREs at all levels. One possible reason is that, compared with the type-B PHREs, the type-A PHREs appeared in warmer regions with a stronger upper-level jet and low-level jet (Figs. 4 and 5). For both types of PHREs, the KE and APE reached a maximum in the lower troposphere, because the weather systems directly triggering a PHRE (shear line, front, convergent line, etc.) were mainly located in the lower levels. The K T of the type-B PHREs was stronger than that of the type-A PHREs, whereas the A T of the type-A PHREs was larger. This indicates that, dynamically, the eddy flow accounting for the type-B PHREs was more intense; whereas, thermodynamically, the precipitation-related eddy flow in type-A PHREs had stronger baroclinicity.

    The layer-based energy paths of the two types of PHREs are summarized in Fig. 9. The common and universal energy paths of the two types of PHREs can be summarized as follows. For the APE of the background circulation, diabatic generation [G(A M)] was the main energy source for A M at all levels. The BCEC process from A M to K M was dominant for the sustainment of K M. The B(K M) and D(K M) were the main factors for the consumption of K M. A proportion of A M was transferred to A T via the interaction energy (A I) (except for in the middle troposphere), which was the downscaled ECP of APE. For the KE of the precipitation-related eddy flow, the BCEC from A T to K T was the main energy source for its persistence in the upper and middle troposphere. Significant downscaled ECPs of KE appeared in the lower troposphere, which sustained the precipitation-related eddy flow directly.

    The main differences in the energy paths of the two types of PHREs appeared in the lower troposphere. The BCEC of eddy flow in the type-A PHREs was mainly from KE to APE, which resulted in larger A T south of the Yangtze River. However, this conversion meanwhile reduced the intensity of K T. In contrast, the BCEC of the type-B PHREs was mainly from APE to KE, which resulted in stronger K T north of the Yangtze River.

    Figure 8.  As in Fig. 7, but for type-B PHREs.

    Figure 9.  Main energy paths in the different levels for type-A PHREs (left column, TL_A, UL_A, ML_A and LL_A means the energy path of type-A integrated at total levels, upper levels, middle levels and lower levels.) and type-B PHREs (right column, TL_B, UL_B, ML_B and LL_B means the energy path of type-B integrated at total levels, upper levels, middle levels and lower levels.). D(K M) denotes the dissipation of K M. B(K M) is the three-dimensional transport associated with X. BCEC is short for baroclinic energy conversion; DNEC means downscaled energy cascade and UPEC is upscaled energy cascade.

5. Conclusion and discussion
  • Based on the classification of PHREs from (Wang et al., 2014), four type-A (main rainbelt south of the Yangtze River) and four type-B (main rainbelt north of the Yangtze River) PHREs, all of which lasted for a three-day period, were selected for energy budget calculations. The energy budget was calculated using a recently introduced set of energy equations based on temporal scale separation. Through these energy analyses, the energy paths that sustained the two types of PHREs were determined, and the main results were as follows.

    Owing to the differences in the vertical configuration of the background circulation, although A M and K M reached a maximum in the upper troposphere and decreased downward, the type-A PHREs generally had stronger A M and K M than the type-B PHREs. The two main similarities in the energy paths of the two types of PHREs were: (2) the BCEC from the APE to KE was the dominant energy source for the evolution of background circulation at all levels; and (3) the downscaled ECPs of KE and APE were vital in the evolution of the eddy flow, which directly triggered the PHREs. The significant differences in the energy paths of the type-A and -B PHREs mainly appeared in the lower troposphere. The BCEC processes associated with the precipitation-related eddy flow in type A PHREs was from KE to APE, which reduced the intensity of K T south of the Yangtze River. In contrast, the BCEC processes of the type-B PHREs were mainly from APE to KE, which enhanced K T north of the Yangtze River.

    Additionally, another set of four three-day cases were selected to composite the energy paths of the type-C PHREs (Fig. 10). Similar to the former two types of PHREs, the diabatic generation G(A M) was the main energy source for the APE of the background circulation (A M) at all levels, except one PHRE in 1996. The BCEC process from A M to K M was also the main source for the sustainment of K M. Moreover, another similarity was the downscaled ECP of APE appeared in the lower and upper levels instead of the middle troposphere. The BCEC from A T to K T was also the main energy source for the persistence of the KE of the precipitation-related eddy flow in the upper and middle troposphere. Different from the significant variety of the type-A and -B PHREs, type C had more consistent downscaled ECPs of KE, which appeared in the lower to middle troposphere. As explained in the above sections, the BCEC of eddy flow in the type-A PHREs was mainly from KE to APE, but the BCEC of the type-B PHREs was mainly from APE to KE. The type C PHREs showed hybrid features between type A and B: the eddy flow of the two cases of type-C PHREs received its KE from APE through BCEC, while a reverse BCEC from KE to APE appeared in the other two cases.

    Figure 10.  Main energy paths in the different levels for type-C PHREs. TL_C, UL_C, ML_C and LL_C means the energy path of type-C integrated at total levels, upper levels, middle levels and lower levels.

    The present study primarily focused on and explored the main energy paths of two types (type A and type B) of PHREs over the Yangtze River-Huaihe River basin——particularly the interactions between the precipitation-related eddy flow and its background circulation. As discussed in section 2.2, this background circulation is a combined system that includes various signals of different temporal scale (in this study, the three-day running mean made the background circulation only have signals with periods larger than three days). In fact, each of the signals in the background circulation has an impact on the precipitation-related eddy flow, and the feedback from the eddy flow also affects the signals in the background circulation. Therefore, further studies should be conducted to determine the dominant background circulation signal for a PHRE. This would be useful for the forecasting and understanding of PHREs. In future work, these knowledge gaps will be addressed by applying the frequency-power analysis and filter method to the energy budget system of (Murakami, 2011).

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