About

Sukyoung Lee is a Distinguished Professor of Meteorology and a John T. Ryan, Jr. Faculty Fellow in the College of Earth and Mineral Sciences at Penn State. Her research specialties include Atmospheric Dynamics, Climate, and Oceanography. She holds a PhD from Princeton University. Her work focuses on understanding atmospheric processes, climate phenomena, and ocean-atmosphere interactions, contributing to the broader field of meteorology and atmospheric science.

Research topics

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

Selected publications

• A comparison of the meridional meandering of extratropical precipitation during boreal winter: eddy momentum flux versus Eulerian storm tracks

  npj Climate and Atmospheric Science · 2025-03-13

  articleOpen access

  The latitudinal distribution of winter extratropical precipitation is often regarded as being determined by the location and intensity of the storm track. Here, we compare the precipitation variability associated with the meridional eddy momentum flux (EMF) with that associated with an Eulerian storm track measure. Observations show that when the midlatitude EMF is anomalously poleward, the occurrence of moderate-to-heavy precipitation (1–33 mm day-1) increases between 45°N and 70°N, while decreasing between 25°N and 45°N. This shift occurs mostly downstream of the climatological storm track maximum, with generally greater precipitation anomalies compared to those associated with storm track changes. The shift is tied to changes in horizontal moisture transport primarily by planetary scale waves. These results suggest that, in addition to the storm track intensity, dynamics of the horizontal wave tilts which affect the EMF intensity need to be considered when projecting future changes in precipitation variability.

  PublisherOA PDFDOI

• Distinct Features of the Summer Arctic Oscillation

  Journal of Climate · 2025-08-15 · 1 citations

  article

  Abstract The Summer Arctic Oscillation (SAO) has received little attention compared with the Winter Arctic Oscillation (WAO). However, recent studies have reported that the SAO is associated with extreme heat events in the Northern Hemisphere. Using reanalysis and satellite datasets, this study investigates the spatial pattern and dynamical mechanisms of the SAO. While the WAO represents the meridional displacement of the eddy-driven jet at ∼40°N, the SAO shows zonal wind anomalies, one in the subtropics (∼30°N) and the other along the Arctic coast (∼75°N). The center of action in the subtropics is mainly driven by meridional wave propagation, while that near the Arctic is largely dominated by baroclinic eddy generation at the surface. The findings here suggest that Arctic cloud cover plays an important role in the SAO, which increases the low-level meridional temperature gradient through the shortwave cloud radiative effect during the positive SAO phase. Arctic sea ice anomalies show a positive correlation with the SAO across most of the Arctic Ocean, partly offsetting the cloud radiative effect. The SAO index shows a strong positive correlation with the cloud cover in the Arctic and upper-level zonal wind along the Arctic coast, showing a clear double jet structure in the Northern Hemisphere at the positive SAO phase. This study suggests a new perspective on annular mode dynamics in Northern Hemisphere summer and the need for more studies on the summer jet dynamics distinct from winter.

  PublisherDOI

• Equatorward Eddy Heat Flux in the Boreal Winter Subtropics and Its Impacts on the Residual Mean Circulation

  Geophysical Research Letters · 2025-11-23

  articleOpen accessSenior author

  Abstract Poleward heat flux driven by large‐scale eddies is a widely recognized component of the general circulation. Although less known, a weak but persistent equatorward eddy heat flux (EEHF) also exists in the subtropical upper troposphere–lower stratosphere (UTLS). In this study, we solve a Transformed Eulerian Mean (TEM) form of the Kuo–Eliassen equation and find that in the subtropical UTLS, the EEHF alone weaken the boreal winter TEM circulation. This EEHF fluctuates on daily time scales. When the EEHF strength exceeds 1 standard deviation, the UTLS TEM circulation substantially weakens. This EEHF cannot be explained by background temperature gradients. Instead, the evolution of the Eliassen–Palm flux and precipitation rate indicates that it is likely driven by horizontal propagation of planetary‐scale waves which, at least in part, is triggered by tropical convection over the western tropical Pacific.

  PublisherOA PDFDOI

• Large-Scale Eddy Fluxes and Their Impact on Extratropical Precipitation in Boreal Winter

  2025-03-14

  preprintOpen access

  The latitudinal distribution of winter extratropical precipitation is often regarded as being determined by the location and intensity of the storm track. Here, we compare the precipitation variability associated with the meridional eddy momentum flux (EMF) with that associated with an Eulerian storm track measure. Observations show that when the midlatitude EMF is anomalously poleward, the occurrence of moderate-to-heavy precipitation (1–33 mm day-1) increases between 45°N and 70°N, while decreasing between 25°N and 45°N. This shift occurs mostly downstream of the climatological storm track maximum, with generally greater precipitation anomalies compared to those associated with storm track changes. The shift is tied to changes in the integrated water vapor transport associated with the EMF. Our results indicate that, in addition to the established measures of storm track intensity, dynamics of the horizontal wave tilts which affect the EMF intensity need to be considered when projecting future changes in precipitation variability.

  PublisherDOI

• Atmospheric memory and implications to sea surface temperature variability forced by the atmosphere

  Climate Dynamics · 2025-10-01

  articleOpen access

  Abstract Variation of sea surface temperature (SST) results from a host of mechanisms involving both the ocean and atmosphere. The atmospheric forcing on SST is usually hypothesized as white noise to reflect the transient and chaotic nature of the atmosphere in contrast to the large heat inertial of the ocean mixed layer. This study presents evidence that the non-white-noise memory of atmospheric forcing has a substantial contribution to SST variability. According to the computed decorrelation time scale, atmospheric forcing can persist for two to five months in the extratropical North Pacific and North Atlantic. Without considering this atmospheric memory, white noise atmospheric forcing underestimates the observed extratropical SST variance by more than 50%; whereas an atmospheric forcing with observed memory produces an SST variability comparable to observations. Approximately 70% of the extratropical atmospheric memory evidently originates from the tropical oceans, including the Niño3.4 region and the tropical North Atlantic, highlighting the significance of tropical-extratropical teleconnection in maintaining the observed SSTA variability in the extratropics.

  PublisherOA PDFDOI

• Zonal Contrasts of the Tropical Pacific Climate Predicted by a Global Constraint

  Asia-Pacific Journal of Atmospheric Sciences · 2024-07-12 · 2 citations

  articleOpen access1st authorCorresponding

  Abstract The zonal gradients in sea surface temperature and convective heating across the tropical Pacific play a pivotal role in setting the weather and climate patterns globally. Under global warming, the current generation of climate models predict that the zonal gradients will decrease, but the trajectory of the observed trends is the opposite. Theories supporting either of the two projections exist, but there are many relevant processes whose net effect is unclear. In this study, a global constraint – the maximum material entropy production (maxMEP) hypothesis—is considered to help close the gap. The climate system considered here is comprised of a one-layer atmosphere and surface in six regions that represent the western tropical Pacific, eastern tropical Pacific, northern and southern midlatitudes, and northern and southern polar regions. The model conserves energy but does not explicitly include dynamics. The model input is observation-based radiative parameters. The radiative effect of greenhouse gas (GHG) loading is mimicked by prescribing increases in the longwave absorptivity $$\epsilon$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ϵ</mml:mi> </mml:math> . The model solutions predict that zonal contrasts in surface temperature, convective heat flux, and surface pressure increase with increasing $$\epsilon$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ϵ</mml:mi> </mml:math> . While maxMEP solutions in general cannot provide a definite answer to the problem, these model results strengthen the possibility that the trajectory of the observed trend reflects the response to increasing GHG loading in the atmosphere.

  PublisherOA PDFDOI

• Benchmark Thermodynamic Contributors to the Growth and Decay of the Regional Extreme Surface Temperature

  Journal of Climate · 2024-02-09 · 7 citations

  articleOpen access

  Abstract A thermodynamic energy budget analysis is applied to the lowest model level of the ERA5 dataset to investigate the mechanisms that drive the growth and decay of extreme positive surface air temperature (SAT) events. Regional and seasonal variation of the mechanisms are investigated. For each grid point on Earth’s surface, a separate composite analysis is performed for extreme SAT events, which are days when temperature anomaly exceeds the 95th percentile. Among the dynamical terms, horizontal temperature advection of the climatological temperature by the anomalous wind dominates SAT anomaly growth over the extratropics, while nonlinear horizontal temperature advection is a major factor over high-latitude regions and the adiabatic warming is important over major mountainous regions. During the decay period, advection of the climatological temperature by the anomalous wind sustains the warming while nonlinear advection becomes the dominant decay mechanism. Among diabatic heating processes, vertical mixing contributes to the SAT anomaly growth over most locations while longwave radiative cooling hinders SAT anomaly growth, especially over the ocean. However, over arid regions during summer, longwave heating largely contributes to SAT anomaly growth while the vertical mixing dampens the SAT anomaly growth. During the decay period, both longwave cooling and vertical mixing contribute to SAT anomaly decay with more pronounced effects over the ocean and land, respectively. These regional and seasonal characteristics of the processes that drive extreme SAT events can serve as a benchmark for understanding the future behavior of extreme weather.

  PublisherOA PDFDOI

• Determination of the Optimal Conditions for the Mass Culture of Large-Type Rotifers (Brachionus plicatilis) at Low Temperatures

  Water · 2023-09-19 · 5 citations

  articleOpen access

  We aimed to determine the optimal conditions for the mass culture of rotifers, which can be used as feed for cold-water fish species at low temperatures. The growth and specific growth rates (SGRs) of rotifers were assessed considering water temperature, salinity, density, dissolved oxygen (DO) levels, and the amount of Chlorella supplied as feed. The growth of rotifers was higher at 15 °C than at 10 °C and at salinities of ~11–17 psu. Initial inoculation densities of 500 and 700 individuals/mL resulted in the highest rotifer density, and SGR was highest at 100 individuals/mL. DO concentration did not significantly affect the growth and SGRs of rotifers. Enrichment with fatty acids is important to supplement the diet of cold-water fish species. Highly unsaturated fatty acid content increased with enrichment time to 14.04 ± 0.86% at 12 h and 15.58 ± 2.20% at 24 h. Thus, the optimal conditions for rotifer mass culture are a water temperature of 15 °C, salinity of 11–17 psu, initial inoculation density of 300–500 individuals/mL, DO concentration of 8 mg/L or more, and Chlorella supply at 7.5 × 1012 cells/mL. Therefore, the present study suggests optimal culture conditions of rotifers at low temperatures for breeding cold-water fish species.

  PublisherOA PDFDOI

• Why does the upward surface turbulent heat flux resulting from sea ice loss over the <scp>Barents and Kara</scp> Seas last only for a few days?

  Quarterly Journal of the Royal Meteorological Society · 2023-03-13 · 1 citations

  articleSenior author

  Abstract This study explores the reason why strong upward anomalous surface turbulent heat fluxes (STHFs) over the Barents and Kara Seas (BKS) occur for a period of only a few days after wind‐driven sea ice loss, even though anomalously low sea ice persists for more than one month. Composite analysis with ERA5 reanalysis data reveals that the sea ice decline coincides with the poleward advection of warm, moist air on the eastern flank of a synoptic‐scale surface low. This results in the anomalous surface air temperature (SAT) exceeding the anomalous skin temperature (SKT) and a downward anomalous STHF. As the surface low propagates eastward, the wind direction changes, resulting in the advection of cold, dry air, the anomalous SKT exceeding the anomalous SAT and a brief period with a strong upward anomalous STHF. This period of strong upward anomalous STHF is cut short, as the surface low propagates southeastward out of the BKS. The eastward propagation of the surface low is crucial, as it allows for northward driving of sea ice to be followed by cold advection and a strong upward anomalous STHF. These results indicate that when wind‐driven sea ice motion exposes the ocean to the atmosphere, except for a brief episode, the reduction of sea ice does not coincide with an increase in a strong upward anomalous STHF.

  PublisherDOI

• COMPARISON OF BUILDING WIND ANALYSIS USING URANS AND ILES

  Journal of computational fluids engineering · 2023-06-30

  articleSenior author

  In this study, two turbulent flow simulation methods, unsteady Reynolds-averaged Navier-Stokes (URANS) simulation and implicit large eddy simulation (ILES), were compared to resolve separated flow around a high-rise building at 1:1:2 shape. In the URANS analysis, a second-order accurate finite volume method with the κ - ω SST turbulence model was applied. In the ILES analysis, a third-order accurate flux reconstruction method, on the other hand, was adopted. Time-averaged velocity profiles at various positions were compared with the wind-tunnel experiment. It was found that both approaches can successfully resolve incoming boundary layer. However, the URANS did not capture the velocity profiles on the roof as well as behind the building well. The ILES gave a relatively closer velocity profile to the wind tunnel result for those regions due to better resolution of wake turbulent structures. Time-averaged streamlines around the building were also presented to compare overall flow structures.

  PublisherDOI

Recent grants

• The Dynamics of Westerly Jets

  NSF · $473k · 2007–2011

• The Mechanisms that Drive Summer Teleconnections: Patterns Associated with High Surface Temperatures

  NSF · $780k · 2020–2024

• The Dynamics of Jets and Waves in the Atmosphere and Southern Ocean

  NSF · $500k · 2015–2019

• On the Dynamics and Implications of the Relationship Between the Subtropical and Polar-Front Jet

  NSF · $339k · 2003–2007

• Investigation of the mechanisms that drive intraseasonal Arctic surface air temperature variability during the winter

  NSF · $607k · 2017–2021

Frequent coauthors

• Steven B. Feldstein

  Pennsylvania State University

  71 shared

• Steven B. Feldstein

  Pennsylvania State University

  28 shared

• Kyle L. Swanson

  Stanford University

  25 shared

• Edmund K. M. Chang

  Stony Brook University

  25 shared

• Changhyun Yoo

  Ewha Womans University

  17 shared

• Christian Franzke

  Pusan National University

  15 shared

• Cory Baggett

  NOAA National Centers for Environmental Prediction

  12 shared

• Seok-Woo Son

  Seoul National University

  11 shared

Education

• PhD, Atmospheric and Oceanic Sciences

  Princeton University

  1991

Awards & honors

• John T. Ryan, Jr. Faculty Fellow in the College of Earth and…