About

Edmund Chang is a professor at Stony Brook University, affiliated with the Office of the Dean SOMAS Atmospheric Sciences. His main research focus is on investigating mid-latitude storms, including how to forecast them better from a few days out to a season, how they may change under global warming, and their societal impacts. He employs a wide range of tools in his research, such as analyses of gridded atmospheric analyses, state-of-the-art climate model simulations, examination of actual observations for validation, and dynamical studies using intermediate and mechanistic models to better understand observed phenomena. His research encompasses major topics such as extratropical cyclones—forecasting and impacts, the dynamics and life cycle of baroclinic waves and cyclones, storm track variability and trends, wave/mean flow interactions, and tropical/extratropical interactions, including tropical meteorology. Chang holds a PhD from Princeton University, earned in 1993, and has contributed extensively to the field through numerous research outputs, grants, and collaborations. His work is characterized by a comprehensive approach to understanding atmospheric dynamics and climate variability, with a particular emphasis on storm systems and their societal implications.

Research topics

• Environmental science
• Geology
• Climatology
• Atmospheric sciences
• Geography
• Meteorology

Selected publications

• Is the Observational Record since the Satellite Era Sufficient to Estimate the MJO Impact on Subseasonal Precipitation Prediction Skill over the CONUS?

  Monthly Weather Review · 2025-10-10

  articleSenior author

  Abstract The Madden–Julian oscillation (MJO) is recognized as a major source of predictability in subseasonal forecasts. Many studies investigate how the MJO modulates prediction skill, often referred to as the “forecast windows of opportunity” driven by the MJO, which can be useful for operational forecasts. In this study, we use observational data and the Community Earth System Model, version 2, Large Ensemble (CESM2-LE) to explore the MJO influence on weeks 3–4 precipitation prediction skill over the contiguous United States (CONUS) with statistical prediction models. The prediction skill, represented by the Heidke skill score (HSS), shows substantial variations due to the MJO modulation for different 40-yr periods, which can be well explained by probability theory. Based on the theoretical explanation, the uncertainty in the MJO modulation of the prediction skill, mostly due to the limited number of MJO events in different 40-yr periods, exceeds the true MJO influence. With such a low signal-to-noise ratio, high prediction skill cannot be attributed solely to the MJO modulation but also involves constructive interference between the MJO and other climate variability. This interference is random across different time periods; thus, constructive interference tends to diminish in subsequent periods, leading to a lower than expected skill in future real-time applications of the prediction tool over regions where high prediction skill is identified during the satellite observed period. We emphasize the need for caution when interpreting the MJO modulation of prediction skill and recommend considering the uncertainty of the modulation highlighted in this study. Significance Statement Skillful subseasonal prediction offers significant social and economic benefits. The states of various climate phenomena can enhance prediction skill, thus prompting studies aimed at quantifying the related increase in prediction skill in the past for indications of real-time forecast skill. However, our findings reveal that evaluating past skills based solely on specific climate states introduces substantial uncertainty, primarily due to the limited number of independent forecasts in the historical record. This uncertainty can lead to a significant decrease in real-time prediction skill where prediction skill is high in current observations. We demonstrate that caution is necessary when interpreting past high skill levels under certain states of climatic phenomena, as they may not reliably indicate the real-time performance of prediction tools.

  PublisherDOI

• Wave Packets and Life Cycles of Troughs in the Framework of Local Finite-Amplitude Wave Activity

  Journal of the Atmospheric Sciences · 2025-03-17

  articleOpen access

  Abstract Synoptic eddies embedded in a westerly flow undergo downstream developments due to their dispersive nature. This paper examines the finite-amplitude aspects of downstream development with the budget of local wave activity (LWA), including explicit contributions from diabatic heating. LWA captures well individual troughs/ridges and the wave packet, and its column budget affords simplified interpretations. In the LWA framework, (linear) downstream development demonstrated in previous analyses is represented by the LWA advection by the zonal reference flow plus LWA flux induced by the radiation of Rossby waves. In addition, convergence of nonlinear advective LWA flux, baroclinic sources at the lower boundary, meridional redistribution by eddy momentum flux, and diabatic sources and sinks complete the column budget of LWA. When applied to the life cycles of troughs within coherent wave packets in the Southern Hemisphere, the LWA budget reveals that individual troughs grow mainly through downstream development, convergence of nonlinear advective flux by eddies, and diabatic heating. Downstream development and divergence of nonlinear flux also dominate trough decay. Contributions from nonlinear advective eddy flux are large in the presence of a strong ridge either immediately upstream or downstream of the trough. Furthermore, anticyclonic components of advective LWA fluxes associated with the upstream or downstream ridge transfer LWA into or out of the trough. Diabatic contributions are significant when the heating exhibits a tilted vertical structure that gives rise to enhanced vertical gradient in heating.

  PublisherOA PDFDOI

• Sensitivity of Northern Hemisphere Extratropical Cyclone Properties to Atmospheric Resolution in the GFDL SPEAR Model

  Journal of Climate · 2025-08-13 · 2 citations

  article

  Abstract Extratropical cyclones (ETCs) significantly influence midlatitude weather and climate through their roles in transporting heat, moisture, and momentum. Accurately simulating ETCs in global climate models (GCMs) is essential for reliable weather forecasts and climate predictions/projections. Previous studies have shown that increasing the horizontal resolution of GCMs can enhance the representation of ETC characteristics. However, the impact of atmospheric resolution finer than 100 km on ETC genesis and frequency, especially when considering the effects of post-processing spectral truncation during cyclone tracking (e.g., T42 or T63), remains underexplored. This study addresses these gaps by examining the sensitivity of Northern Hemisphere ETCs to atmospheric resolutions of 100 km, 50 km, and 25 km using the fully coupled GFDL SPEAR model. Cyclone tracking is performed at spectral truncations of T42, T63, and T106 to assess the effects of spectral smoothing. Results reveal that increasing atmospheric resolution has minimal impact on the frequency of large-sized ETCs but leads to a substantial increase in the frequency of small-sized ETCs, particularly over the North Pacific and the North Atlantic. The size-dependent sensitivity of ETCs to atmospheric resolution is the most pronounced at T106, and further analyses suggest that the genesis of these small-sized ETCs are highly impacted by diabatic heating. Comparisons with various reanalysis datasets suggest that high-resolution models are likely better at capturing small-sized ETCs rather than overestimating their frequency. These findings highlight the critical importance of considering size-dependent sensitivities when interpreting ETC biases in high-resolution model outputs compared to reanalysis data and underscore the potential role of diabatic heating in genesis of small-sized ETCs.

  PublisherDOI

• Local Finite‐Amplitude Wave Activity of Water Vapor as a Diagnostic of Atmospheric River Events

  Geophysical Research Letters · 2025-04-28 · 1 citations

  articleOpen accessSenior authorCorresponding

  Abstract We generalize the formalism of local wave activity of quasi‐geostrophic potential vorticity to water vapor, defined as LWA‐V, and derive the LWA‐V budget equation. LWA‐V measures the waviness of moisture contours from the zonal symmetry in the eddy‐free atmosphere. It delineates well the northward moisture intrusion and the filamentary feature of AR events. Compared with the traditional moisture budget, the climatological LWA‐V and LWA‐V budget terms are more consistent in structure and are able to delineate the climatological AR. Moisture flux convergence is the dominant process for the intensification and movement of the LWA‐V center associated with the AR event while the combined effect of evaporation and precipitation is mainly a sink of LWA‐V, which is consistent with traditional moisture budget analysis. Furthermore, utilizing the Lagrangian aspect of LWA‐V, we demonstrate quantitatively that the original latitudes of the largest precipitable water of the AR event are in the tropical region.

  PublisherOA PDFDOI

• Using Finite-Amplitude Wave Activity to Examine the Impact of Latent Heating on Baroclinic Wave Activity

  Journal of the Atmospheric Sciences · 2025-07-11

  articleSenior author

  Abstract Using the dynamical diagnostic method of finite-amplitude local wave activity (LWA) and a moist two-layer quasigeostrophic (QG) model, we investigate the impacts of diabatic heating on the mean states and the mean LWA budget, as well as statistical features and life cycles of baroclinic waves. Despite the overall positive LWA tendency due to diabatic heating, the total generation (baroclinic plus diabatic) of LWA decreases due to the impact of precipitation reducing the baroclinicity of the mean state, and thus, eddies are weaker in the moist model compared to the dry model forced with the same radiative forcing. On average, troughs are stronger than ridges in the dry model. However, this ceases to hold in the moist model due to the positive contributions of diabatic heating to the growth of ridges. Diabatic heating can dominate ridge growth in the upper layer, due to the generation of negative potential vorticity, but not troughs. It differs from the result of reanalysis data that diabatic heating can dominate the growth of some troughs. This difference is largely because of the lack of vertical structure in the diabatic heating profile in the two-layer model. Nevertheless, diabatic heating can still contribute to the growth of some troughs in the upper layer due to the nonlocal nature of its impact under the LWA framework. Significance Statement The impacts of diabatic heating on troughs and ridges are examined in the nonlinear regime using the framework of local wave activity. As the moisture content in the moist two-layer quasigeostrophic model increases, the instability of the mean state decreases. Thus, the mean wave activity weakens despite the positive contribution of diabatic heating. Latent heating generates anticyclonic wave activity but decreases cyclonic wave activity in the upper layer of the moist model, reducing the asymmetry between troughs and ridges. Diabatic heating can be the dominant term for the growth of ridges in the upper layer, but not for troughs. Moreover, the nonlocal effect of diabatic heating on baroclinic wave activity is demonstrated in a mathematically explicit and exact way since LWA is Lagrangian in latitude by design.

  PublisherDOI

• Resolution-Dependent Impact of Extratropical Cyclones on Winter U.S. Precipitation Bias in the GFDL SPEAR Model

  2025-03-15

  preprintOpen accessSenior author

  Extratropical cyclones (ETCs) are the primary drivers of winter precipitation across the United States, accounting for up to 85% of total precipitation. This study uses the GFDL SPEAR models at atmospheric resolutions of 100 km, 50 km, and 25 km to examine how ETC dynamics impact precipitation patterns and biases across the United States. Higher-resolution models reduce ETC-related precipitation biases in the Southwest and Midwest but increase biases in coastal regions, including the West Coast and the Eastern United States. To understand these biases, we decompose ETC-related precipitation biases into those driven by precipitation frequency and intensity. Coastal precipitation biases are mainly due to overestimations of both the occurrence and intensity of precipitation, which are related to ETC frequency and intensity, respectively. In inland areas, biases are largely driven by occurrence bias associated with ETC frequency. Notably, higher-resolution models simulate amplified ETC frequency and intensity biases in coastal regions, while showing a decrease in ETC frequency bias in inland regions. This increase is especially linked to the overestimation of small-scale ETCs, which considerably inflate frequency-driven precipitation bias. Additionally, improvements in AMIP runs suggest that these biases are partly connected to SST bias. These findings emphasize the sensitivity of precipitation representation to ETC dynamics and underscore the importance of addressing resolution-dependent and SST related biases to improve midlatitude precipitation simulations in climate models.

  PublisherDOI

• Improving Statistical Prediction of Subseasonal CONUS Precipitation Based on ENSO and the MJO by Training With Large Ensemble Climate Simulations

  Geophysical Research Letters · 2025-01-16 · 6 citations

  articleOpen accessSenior author

  Abstract Previous studies have highlighted the significant impacts of El Niño–Southern Oscillation (ENSO) and the Madden–Julian Oscillation (MJO) on wintertime precipitation over the contiguous United States (CONUS). Here, we demonstrate skillful statistical prediction of subseasonal precipitation over the CONUS using the information of ENSO and the MJO. Simple statistical tools, such as multiple linear regression, exhibit significant improvement in prediction when trained with large ensemble climate simulations, surpassing those trained solely on observational data. Despite the biases in ENSO and MJO teleconnections in the climate simulations, the abundance of data, exceeding observational records by 100 times, allows more robust statistical relationships to be established, leading to such improvement. The utilization of machine learning tools yields additional gains in prediction skill beyond multiple linear regression. ENSO emerges as a dominant contributor to prediction skill, surpassing the influence of the MJO, whose impact diminishes with increasing forecast lead time.

  PublisherOA PDFDOI

• Warm conveyor belt activity over the Pacific: modulation by the Madden–Julian Oscillation and impact on tropical–extratropical teleconnections

  Weather and Climate Dynamics · 2024-01-19 · 6 citations

  articleOpen access

  Abstract. Research in the last few decades has revealed that rapidly ascending airstreams in extratropical cyclones – so-called warm conveyor belts (WCBs) – play an important role in extratropical atmospheric dynamics. However on the subseasonal timescale, the modulation of their occurrence frequency, henceforth referred to as WCB activity, has so far received little attention. Also, it is not yet clear whether WCB activity may affect tropospheric teleconnection patterns, which constitute a source of predictability on this subseasonal timescale. Using reanalysis data, this study analyzes the modulation of WCB activity by the Madden–Julian Oscillation (MJO). A key finding is that WCB activity increases significantly over the western North Pacific when the convection of the MJO is located over the Indian Ocean. This increased WCB activity, which is stronger during La Niña conditions, is related to enhanced poleward moisture fluxes driven by the circulation of subtropical Rossby gyres associated with the MJO. In contrast, when the convection of the MJO is located over the western North Pacific, WCB activity increases significantly over the eastern North Pacific. This increase stems from a southward shift and eastward extension of the North Pacific jet stream. However, while these mean increases are significant, individual MJO events exhibit substantial variability, with some events even exhibiting anomalously low WCB activity. Individual events of the same MJO phase with anomalously low WCB activity over the North Pacific tend to be followed by the known canonical teleconnection patterns in the Atlantic–European region; i.e., the occurrence frequency of the positive phase of the North Atlantic Oscillation (NAO) is enhanced when convection of the MJO is located over the Indian Ocean and similarly for the negative phase of the NAO when MJO convection is over the western North Pacific. However, the canonical teleconnection patterns are modified when individual events of the same MJO phase are accompanied by anomalously high WCB activity over the North Pacific. In particular, the link between MJO and the negative phase of the NAO weakens considerably. Reanalysis data and experiments with an idealized general circulation model reveal that this is related to anomalous ridge building over western North America favored by enhanced WCB activity. Overall, our study highlights the potential role of WCBs in shaping tropical–extratropical teleconnection patterns and underlines the importance of representing them adequately in numerical weather prediction models in order to fully exploit the sources of predictability emerging from the tropics.

  PublisherDOI

• Comment on “Anticyclonic Suppression of the North Pacific Transient Eddy Activity in Midwinter” by Okajima et al.

  Geophysical Research Letters · 2024-10-14 · 1 citations

  articleOpen access1st authorCorresponding

  Abstract Atmospheric energetics is frequently used to diagnose how different atmospheric processes contribute to the development of transient storm track activity. Okajima et al. (2024), https://doi.org/10.1029/2023gl106932 developed an ad hoc method to separate the contributions of cyclones and anticyclones to the energetics using the value of the curvature of the instantaneous local wind. Here, using simple examples in which the physics is exactly known, it is shown that cyclones embedded within a constant zonal flow exhibit large regions with anticyclonic curvature despite the absence of any real anticyclones. Using the method of Okajima et al., a large fraction of the eddy kinetic energy is erroneously attributed to being associated with anticyclones. Furthermore, the fraction that is misattributed varies substantially with changes in the background wind speed. It is concluded that using the curvature to separate energetics contributions from cyclones and anticyclones is not likely to be physically meaningful.

  PublisherOA PDFDOI

• Comments on “horizontal gravity disturbance vector in atmospheric dynamics” by Peter C. Chu

  Dynamics of Atmospheres and Oceans · 2023-06-17 · 3 citations

  articleOpen access1st authorCorresponding
  PublisherOA PDFDOI

Recent grants

• Analyzing the Structure and Evolution of Southern Hemisphere Synoptic Variability Using a New Reanalysis Observations Database

  NSF · $261k · 2004–2008

• New Perspectives on Storm Track Dynamics, Variability, and Change

  NSF · $573k · 2013–2018

• Dynamics of Interactions between Wave Packets and Explosive Cyclogenesis over Western North Pacific

  NSF · $446k · 2008–2013

Frequent coauthors

• Yanjuan Guo

  Guangzhou Education Bureau

  61 shared

• Toshiaki Shinoda

  51 shared

• Duane E. Waliser

  Jet Propulsion Laboratory

  49 shared

• Volkmar Wirth

  25 shared

• Cheng Zheng

  25 shared

• Michael Riemer

  25 shared

• Sukyoung Lee

  Pennsylvania State University

  25 shared

• Kyle L. Swanson

  Stanford University

  25 shared

Education

• Ph. D., Atmospheric and Oceanic Sciences Program

  Princeton University

  1993

Awards & honors

• Nobel Peace Prize (2007)