Research Highlights

My research has generally focused on convective processes and its role in climate variability and changes. A major effort of my current research is on the dynamics and convective-radiative processes responsible for the evolution of the Madden Julian Oscillations (MJO). Another current research focus is about the dynamics of ENSO and Pacific decadal oscillations. Research highlights from my current research activities and those from my previous research projects are introduced below.

Characteristics and Origin of Intraseasonal Oscillations in Tropical Atmosphere

Intraseasonal oscillation (ISO), in particular, that with 30-60 day periods, has been proposed an intrinsic mode of tropical oscillations maintained by convection interacting with tropical waves. It has been shown the ISO can be maintained by the so-call mobile wave-CISK mechanism. But it is not clear that the same results will hold for a more realistic treatment of diabatic heating where the vertical distribution is a function of the thermodynamic states of the model atmosphere and lower boundary conditions. We presented an improved treatment of convective heating and carried out further experiments to extend the previous theory. The study illustrates the role of a dynamically interactive heating process in the lower atmosphere in modifying the basic dynamics of intraseasonal oscillations. We also investigated 10-20 day ISO (also known as quasi-biweekly oscillation (QBWO)) through a detailed statistical analysis of the structures and energy budget of QBWO over Western North Pacific (WNP). By a systematic comparison of observations with theoretical considerations, QBWO over the WNP during summertime can be traced to equatorial-Rossby wave originally movingwestward and turn northwestward.

  • Tseng, K.-C., C.-H. Sui, and T. LI, 2015: Moistening Processes for Madden-Julian Oscillations during DYNAMO/CINDY. J. Climate, 28, 3041-3057, DOI: 10.1175/JCLI-D-14-00416.1 (Link to abstract)
  • Sui, C.-H. and K-M. Lau, 1989: Origin of low frequency (intraseasonal) oscillations in the tropical atmosphere. Part II: Structure and Propagation of Mobile Wave-CISK Modes and Their Modification by Lower Boundary Forcings. J. Atmos. Sci., 46, 37-56. (Link to abstract)
  • Chen, G. and C.-H. Sui, 2010: Characteristics and Origin of Quasi-biweekly Oscillation over the Western North Pacific during Boreal Summer. J. Geophys. Res. 115, D14113, doi:10.1029/2009JDO13389. (Link to abstract)

Interannual variability and East Asian monsoon

We show the western North Pacific Subtropical High (WNPSH) in summer exhibits significant 2-3 years and 3-5 years oscillations with interdecadal variability. The 2-3-year oscillation is most evident after 1990. It is accompanied by anomalous meridional overturning circulation characterized by warm SST anomalies (SSTA) and ascending motion in the maritime continent and anomalous descending motion near the Philippine Sea, and by evolving warm to cold SSTA in the central-eastern Pacific from the preceding winter to the summer. The 3-5-year oscillation is most pronounced during the 1980s. It is accompanied by anomalous descending motion over the maritime continent and warm SSTA in the central-eastern equatorial Pacific that persists from the preceding winter to the summer; the complementary cooling and descending motion in the western Pacific are related to anomalous east-west circulation associated with ENSO.

  • Chen, H.-C., Z.-Z. Hu, B. Huang, C.-H. Sui, 2016: The role of reversed equatorial zonal transport in terminating an ENSO event. J. Climate, 29, 5859-5877. doi:10.1175/JCLI-D-16-0047.1 (Link to abstract)
  • Chen, H.-C., C.-H. Sui, Y.-H. Tseng, and B.-H. Huang, 2015: An Analysis of the Linkage of Pacific Subtropical Cells with the Recharge-discharge Processes in ENSO Evolution. J. Climate, 28, 3786-3805, doi:10.1175/JCLI-D-14-00134.1 (Link to abstract)
  • Chung, P.-H., C.-H. Sui, and T. Li, 2011: Interannual relationships between the tropical sea surface temperature and summertime subtropical anticyclone over the western North Pacific, J. Geophys. Res., 116, D13111, doi:10.1029/2010JDO15554. (Link to abstract)
  • Sui, C.-H., P.-H. Chung, and T. LI, 2007: Interannual and interdecadal variability of the summertime western north Pacific subtropical High. Geophys. Res. Lett., 34, L11701, doi:10.1029/2006GLO29204. June 2007. (Link to abstract)

Analysis-modeling of climate trend/variability and associated hydrologic processes

Centennial and inter-decadal Climatic Trends

From the monthly time series of global mean surface temperature in 1880-2009, we indentify a centennial climate warming trend through HHT (Hilbert-Huang Transform). We then applied the EOF analysis to the detrended SST data to further identify two interdecadal climate oscillations: the PDO/IPO (Pacific Decadal Oscillation /inter-decadal Pacific Oscillation), and the MDV (Multidecadal Variability) that has strong signals in Atlantic (and northern Pacific) near 60-year period. We further analyzed NCEP-NCAR and ERA-40 data through combined EOF to investigate the corresponding circulation patterns associated with these climate trends.

  • Liu, Peng, and C.-H. Sui, 2014: An Observational Analysis of Oceanic and Atmospheric Structure of Global-Scale Multidecadal Variability. Adv. Atmos. Sci., 31(2), 316-330. doi:10.1007/s00376-013-2305-Y (Link to abstract)

Climatic (trend and variability) Analysis of Cloud and Rainfall

We identify the broad scale features of hydrologic cycle and also perform a trend analysis of cloud/rainfall distribution in different climate regimes (like EA monsoon in China and Taiwan) to identify extreme rainfall changes in recent decades

  • Chang, C.-P., Y. Lei, C.-H. Sui, X. Lin, F. Ren, 2012: Tropical cyclone and extreme rainfall trends in East Asian summer monsoon since mid-20th century. Geophys. Res. Lett., 39(18), doi:10.1029/2012GL052945 (Link to abstract)

Simulation for climatic Trends and Variability of Cloud and Rainfall Process

The characteristics of rainfall trend changes suggest combined influences of global warming and climate oscillations (ENSO and Pacific decadal variability) on water cycle in western north Pacific region encompassing southern China and Taiwan. We have performed modeling studies based on the Weather Research and Forecast (WRF V3.2.1) model which is configured to consist of a nested high-resolution, cloud-resolving sub-domains covering western North Pacific. A series of experiments are performed to simulate the water cycle in warm season at different stages of climate oscillations. The simulated results are evaluated against temperature and humidity fields in the reanalysis data and aircraft dropsonde measurements. retrieved cloud content and rainfall from CloudSat and TRMM products. ![Graph01] (/img/research-01.jpg)

We evaluates the WRF simulated cloud properties (like raindrop size distribution) by several bulk microphysics scheme (CAMS, Morrison, and WDM6) against an observed mesoscale convective system (MCS) that occurred on 14 June 2008 during the Southwest Monsoon Experiment (SoWMEX) and Terrain-influenced Monsoon Rainfall Experiment (TİMREX). The model reflectivity (ZH), differential reflectivity (ZDR), and microwave brightness temperature (TB) are compared with the corresponding observations by the S-band dual-polarization Doppler radar (S-Pol) and the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The evaluation is further based to improve the original CAMS bulk microphysics scheme.

  • Gao, W, and C.-H. Sui, 2013: A modeling analysis of rainfall and water cycle by the cloud-resolving WRF model over western North Pacific. Adv. Atmos. Sci., 30(6), 1695-1711. doi:10.1007/s00376-013-2288-8. (Link to abstract)
  • Gao, W. C.-H. Sui, T.-C. C. Wang, W.-Y. Chang, 2011: An Evaluation and improvement of Cloud Properties from a Two-moment Cloud Microphysics scheme (CAMS) by observations from SOWMENTİMREX. J. Geophys. Res. 116. D19101, 13 PP., 2011. doi:10.1029/20 11 JD015718. (Link to abstract)

Interactions of Multiscale Phenomena in Tropical Atmosphere

It was found that the convection associated with ISOs often appears in organized large-scale complexes called super cloud clusters (SCC). The wind field at 850mb associated with the SCCs is characterized by steady easterlies to the east of the convection and fluctuating westerlies to the west. Several studies of the daily surface winds in the western and central equatorial Pacific have documented periods in which the climatological steady easterlies are replaced by highly variable “westerly wind bursts” (WWB). It possess strong seasonal as well as interannual variabilites. We focused on analyses of low-frequency (<90 days) and high-frequency (one to several days) disturbances in the context of ISO, SCC, WWB, and the interactions among them. Result revealed a hierarchy of temporal scales embedded in the tropical atmospheric intraseasonal oscillations. Extending the above study, we investigate the effect of MJO and embedding tropical waves on TC genesis. The warm season of 2004 is chosen for a comprehensive analysis because of a strong MJO, active tropical waves, and five TCs observed in June 2004 (relative to 1.8 TCs in June on the average). Our study attributes this record-breaking event of TC genesis to a favorable warm SSTA over the western Pacific, and the strong multiscale MJO. We further analyzed measurements collected during TOGA COARE, and compared the observed oceanic variations with the response of an ocean mixed-layer model to observed surface heat and momentum fluxes. The studyreveals air-sea interaction processes involving diurnal and intraseasonal oscillations.

  • Ching, L., C.-H. Sui, Ming-Jen Yang, 2010: An analysis of multi-scale nature of tropical cyclone activities in June 2004. Part 1: Climate background. J. Ceophys. Res., 115, D24108, doi:10.1029/2010JD013803. (Link to abstract)
  • Sui, C.-H., X. Li, K.-M. Lau, and D. Adamec, 1997: Multi-scale air-sea interaction during TOGA COARE. Mon. Wea. Rev., 125(5), 448-462. (Link to abstract)
  • Sui, C.-H. and K.-M. Lau, 1992: Multi-scale phenomena in the tropical atmosphere over the western Pacific. Mon. Wea. Rev. 120. 407-430. (Link to abstract)

Tropical Water and Energy Cycles in cloud resolving models

Atmospheric general circulation models (GCMs) have been extensively used for climate studies, which have revealed that a proper treatment of the interactions of convection, radiation, and large-scale dynamics in these models is essential for climate simulations. However GCMs are not suitable for detailed climate feedback studies because of the primitive moist parameterization. An alternative approach is to use cloud resolving models (CRMs) that includes explicit cloud-scale dynamics, detailed microphysics, and sophisticated radiative transfer calculation based on physically determined cloud optical properties. We used the Goddard Cumulus Ensemble (GCE) Model with large horizontal domain and fine (cloud resolving) spatial and temporal resolutions allowing many cloud populations to develop simultaneously to study the water cycle in different weather and climate regimes with emphasis on the water vapor and cloud feedback mechanisms. For such climate applications, we focused on the water and energy cycles in tropical cloud clusters and their sensitivity to imposed boundary conditions and large-scale forcings. We also discussed changes in the water and energy cycles in perturbed climates with a view toward unraveling basic feedback mechanisms over the tropical oceans.

  • Sui, C.-H., X. Li, K.-M. Lau, W-K. Tao, M.-D. Chou, and M.-J·Yang, 2008: Convective-radiative-mixing processes in the tropical ocean-atmosphere. The Monograph for the 50-yr Anniversary of Dept. of Atmospheric Sciences, National Taiwan University, 66-88.
  • Sui, C.-H., X. Li, M.-J. Yang, 2007: On the Definition of Precipitation Efficiency, J. Atmos. Sci, 64 (12), 4506-4513. December 2007. (Link to abstract)
  • Sui, C.-H., X. Li, M.-J. Yang, and H.-L. Huang, 2005: Estimation of Oceanic Precipitation Efficiency in Cloud Models. J. Atmos. Sci. 62, 4358-4370. (Link to abstract)
  • Sui, C.-H., K.-M. Lau, W-K. Tao and J. Simpson, 1994: The tropical water and energy cycles in a cumulus ensemble model. Part 1: Equilibrium climate. J. Atmos. Sci., 51(5), 711-728, 1994. (Link to abstract)

Diurnal Variations of Tropical Oceanic Convection

We investigate the diurnal variation of tropical oceanic convection and its modulation by large-scale environments by analyzing rainfall and cloud statistics, mass and heat budgets, and surface heat fluxes using the Tropical Oceanic Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) observations. Our analysis suggested three mechanisms (cloud-radiation interactions, available precipitable water, and surface heating) involved in diurnal responses to radiative heating cycle. To further clarify the observational analysis, we used a cloud-resolving model (GCE) to examine the relative importance of each mechanism in diurnal variations of convection.

  • Sui, C.-H., X. Li, and K.-M. Lau, 1998: Radiative-convective processes in simulated diurnal variations of tropical oceanic convection. J. Atmos. Sci., 55(13), 2345-2357. (Link to abstract)
  • Sui, C.-H., K.-M. Lau, Y. Takayabu, and D. Short, 1997: Diurnal variations in tropical oceanic cumulus convection during TOGA COARE. J. Atmos. Sci. 54, 637-655. (Link to abstract)