About

Craig Epifanio is an Associate Professor in the Department of Atmospheric Sciences at Texas A&M University. His research centers on the basic fluid dynamics of mesoscale atmospheric phenomena, with particular emphasis on topographic and thermally forced circulations. His work includes studying topographic waves generated by mountain ranges, which can break down into turbulence and pose hazards to aircraft, and understanding the physics of topographic wave instability as a precursor to turbulence. Additionally, he investigates severe storm dynamics, especially the environmental factors influencing tornadogenesis, using numerical simulations and vorticity analysis tools. Epifanio's research also involves computational methods such as Newton-Krylov solvers, time-splitting schemes, and surface-stress condition treatments on complex terrains. His educational background includes a Ph.D. in Atmospheric Science from the University of Washington and a B.S. in Physics from Williams College.

Research topics

• Meteorology
• Geology
• Oceanography
• Geography
• Mechanics
• Climatology
• Mathematics
• Physics
• Geometry

Selected publications

• The Land–Sea Breeze Circulation over the West Coast of Sumatra

  Monthly Weather Review · 2025-08-25

  article

  Abstract The characteristics of the land and sea breeze near the west coast of Sumatra are studied using hourly 10-m wind observations from the Bengkulu Airport for the year 2018, with an emphasis on the properties of the land breeze. Spectral analysis shows that the land–sea breeze cycle is a dominant part of the overall circulation in the region, with disturbances at the diurnal frequency accounting for roughly half the overall disturbance kinetic energy. A method is presented for isolating the near-diurnal parts of the flow through a combination of high- and low-pass filtering, with land and sea breezes defined in terms of the shore-perpendicular component of the filtered winds. By this definition, a land breeze occurs each day, with a median onset time of 1900 LT, a median duration of 15 h, and a median maximum speed of 1.8 m s −1 occurring near 0200 LT. The characteristics of the land breeze are found to depend strongly on the phase of the Madden–Julian oscillation. A dependence was also found during the Asian and Australian monsoons, particularly for the onset time and maximum speed. Sea breezes occur almost every day but are much shorter (about 8.5 h) and stronger (>3 m s −1 ) than land breezes. Comparisons between airport observations and ERA5 surface winds show that while ERA5 accurately captures the onset time, duration, and timing of the maximum speed for sea breezes, it only captures the onset time and duration for land breezes. For both, the maximum speed is significantly underestimated. Significance Statement Detailed characteristics of tropical land and sea breezes are lacking in the literature. Utilizing 1 year of hourly wind observations from the west coast of Sumatra and a newly developed detection algorithm, we found that land and sea breezes occur essentially every day. Land breezes start just after sunset but last many hours after sunrise and reach their maximum speed almost halfway through their median 15-h duration. These properties vary intraseasonally and seasonally. Sea breezes begin around 1000 LT and are much shorter and stronger than land breezes. ERA5 does a reasonable job capturing many characteristics of the land–sea breeze circulation but underestimates the maximum wind speed in both cases.

  PublisherDOI

• Surface Drag on Deformed Topographic Boundaries: Tests Using a Semi-Idealized Model

  Journal of the Atmospheric Sciences · 2024

  Senior authorCorresponding
  • Geology
  • Meteorology
  • Mechanics

  Abstract The physics of the surface drag (or surface stress) boundary condition is explored in the context of semi-idealized flows past realistic terrain. Numerical experiments are presented to explore the impact of the drag condition on flows past a region of complex topography, with a particular focus on the dependence on terrain geometry. Arguments are presented to show that the drag condition depends on the geometry of the terrain in two respects: (i) a dependence on terrain slope, as represented by a normal gradient term, and (ii) a dependence on the curvature, which appears in the drag condition as a Dirichlet term. The dependence on the geometry is illustrated through a series of numerical experiments in which simulations using the full form of the drag condition are compared to companion simulations using one of two widely used approximations: (i) the normal gradient condition, which accounts for the terrain slope but neglects curvature, and (ii) the flat boundary assumption, which neglects both slope and curvature. The results show that the role of the terrain geometry in the drag condition is strongly dependent on grid spacing, with more highly resolved topography leading to a stronger dependence on the slope and curvature. For sufficiently high resolutions, the dependence on the geometry becomes significant, to the extent that simulations using the approximate drag conditions fail to capture important aspects of the flow. Some basic implications of these results for the problem of high-resolution wind energy forecasting are discussed.

  PublisherDOI

• Formation of Nocturnal Offshore Rainfall near the West Coast of Sumatra: Land Breeze or Gravity Wave?

  Monthly Weather Review · 2021 · 39 citations

  • Climatology
  • Geology
  • Oceanography

  Abstract Afternoon deep convection over the Maritime Continent islands propagates offshore in the evening to early morning hours, leading to a nocturnal rainfall maximum over the nearby ocean. This work investigates the formation of the seaward precipitation migration off western Sumatra and its intraseasonal and seasonal characteristics using BMKG C-band radar observations from Padang and ERA5 reanalysis. A total of 117 nocturnal offshore rainfall events were identified in 2018, with an average propagation speed of 4.5 m s −1 within 180 km of Sumatra. Most offshore propagation events occur when the Madden–Julian oscillation (MJO) is either weak (real-time multivariate MJO index < 1) or active over the Indian Ocean (phases 1–3), whereas very few occur when the MJO is active over the Maritime Continent and western Pacific Ocean (phases 4–6). The occurrence of offshore rainfall events also varies on the basis of the seasonal evolution of the large-scale circulation associated with the Asian–Australian monsoons, with fewer events during the monsoon seasons of December–February and June–August and more during the transition seasons of March–May and September–November. Low-level convergence, resulting from the interaction of the land breeze and background low-level westerlies, is found to be the primary driver for producing offshore convective rain propagation from the west coast of Sumatra. Stratiform rain propagation speeds are further increased by upper-level easterlies, which explains the faster migration speed of high reflective clouds observed by satellite. However, temperature anomalies associated with daytime convective latent heating over Sumatra indicate that gravity waves may also modulate the offshore environment to be conducive to seaward convection migration.

  PublisherDOI

• Tests of an Advanced Surface-Stress and Surface-Flux Implementation Accounting for Complex Terrain Geometry

  17th Conference on Mesoscale Processes · 2017-07-26

  article1st authorCorresponding
  Publisher

• Effects of the Low-Level Wind Profile on Outflow Position and Near-Surface Vertical Vorticity in Simulated Supercell Thunderstorms

  Journal of the Atmospheric Sciences · 2017-12-15 · 32 citations

  articleSenior author

  Abstract Supercell thunderstorms are simulated using an idealized numerical model to analyze the effects of modifications to the environmental low-level wind profile on near-surface rotation. Specifically, the orientation, magnitude, and depth of the low-level vertical wind shear are modified in several suites of experiments and compared to control simulations with no vertical wind shear in the prescribed layer. The overall morphology of the simulated supercells is highly sensitive to even shallow changes in the low-level wind profile. Moreover, maximum near-surface vertical vorticity varies as the low-level wind profile is modified. The results suggest this is principally a consequence of the degree to which favorable dynamic forcing of negatively buoyant outflow is superimposed upon the near-surface circulation maximum. Simulations with easterly shear and weaker storm-relative winds over the depth of the gust front promote forward-surging outflow and smaller separation between the near-surface circulation maximum and the mesocyclone aloft compared with other hodograph shapes. This promotes near-surface vertical vorticity intensification in these simulations. Similar trends in near-surface vertical vorticity as a function of low-level shear orientation are observed for varying shear-layer depths and bulk-shear magnitudes over the shear layer. The degree to which specific hodograph shapes promote strong near-surface rotation may vary with different deep-layer wind profiles or thermodynamic environments from those simulated here; however, this study concludes that favorable positioning of the near-surface circulation maximum and mesocyclone aloft are a necessary condition for supercell tornadogenesis and this positioning may be modulated by the low-level wind profile.

  PublisherDOI

• Implementation and Testing of Advanced Surface Boundary Conditions Over Complex Terrain in A Semi-idealized Model

  AGUFM · 2017-12-01

  articleSenior author
  Publisher

• Convective Transport of Trace Species Observed During the Stratosphere-Troposphere Analyses of Regional Transport 2008 Experiment (START08)

  OakTrust (Texas A&M University Libraries) · 2015-12-16

  articleOpen accessSenior author

  During the Stratosphere-Troposphere Analyses of Regional Transport 2008 Experiment (START08) the NCAR/NSF Gulfstream V aircraft encountered high concentrations of NO and NOy in the upper troposphere downwind of a squall line in north Texas, suggesting either convective transport of polluted boundary layer air to the upper troposphere or lightning induced production of nitrogen oxides in the convection. These hypotheses are tested by computing three-dimensional back-trajectories using winds from a high-resolution simulation of the event with the Weather Research and Forecasting (WRF) Model. The WRF model simulation reproduces the storm structure and evolution with good fidelity. The back trajectories reveal two distinct layers of out flow air from different mesoscale convective systems (MCSs). Most air in the upper layer is transported northward from an MCS in south Texas, while the lower layer is from both the squall line and the southern MCS. The predicted concentrations of CO and NOy using a simple chemical model show that the back trajectories capture the vertical profile of CO in the lower layer and of NOy at the bottom and top of the lower layer. The enhanced NOy could be explained by lightning during the time the out flow air was ascending in the convective updrafts using data from the National Lightning Detection Network (NLDN). In the upper layer, the large discrepancy of NOy between observation and model seems to be caused by the lack of lightning source and a notable underestimate of the vertical transport to the very top of the troposphere by the MCS.

  Publisher

• Convective transport of trace species observed during the Stratosphere‐Troposphere Analyses of Regional Transport 2008 experiment

  Journal of Geophysical Research Atmospheres · 2015-09-12 · 2 citations

  articleSenior author

  Abstract During the Stratosphere‐Troposphere Analyses of Regional Transport 2008 experiment (START08) the NCAR/NSF Gulfstream V aircraft observed high concentrations of NO and NO y in the upper troposphere downwind of a weakening squall line in northern Texas, suggesting either convective transport of polluted boundary layer air to the upper troposphere or lightning production of nitrogen oxides in the convection. These hypotheses are tested by computing three‐dimensional back trajectories using winds from a high‐resolution simulation of the event with the Weather Research and Forecasting (WRF) model. The WRF model simulation reproduces the storm structure and evolution with good fidelity. The back trajectories reveal two distinct layers of outflow air from different mesoscale convective systems (MCSs). Most air in the upper layer is transported northward from an MCS in southern Texas, while the lower layer is from both the northern squall line and the southern MCS. In both layers inconsistencies between observed concentrations of CO, NO, and O 3 and predictions from a simple mixing model suggest that there is significant production of NO by lightning in the convective systems. This is consistent with lightning observations from the National Lightning Detection Network. Additionally, the model simulation appears to slightly underestimate the depth of vertical transport by the MCS.

  PublisherDOI

• A comparison of surface-layer implementations over steep terrain

  16th Conference on Mountain Meteorology (17-22 August, 2014) · 2014-08-21

  article1st authorCorresponding
  Publisher

• MOUNTAIN METEOROLOGY | Lee Vortices

  Encyclopedia of Atmospheric Sciences · 2014-09-18 · 5 citations

  book-chapter1st authorCorresponding
  PublisherDOI

Recent grants

• Wakes and Scale Interactions in Stratified Flows Past Topography

  NSF · $307k · 2003–2007

Frequent coauthors

• Dale R. Durran

  University of Washington

  12 shared

• Fuqing Zhang

  8 shared

• Richard Rotunno

  NSF National Center for Atmospheric Research

  4 shared

• Tingting Qian

  Nanjing University of Chinese Medicine

  4 shared

• Chris Snyder

  4 shared

• James D. Doyle

  United States Navy

  3 shared

• Kevin C. Viner

  3 shared

• Yi Li

  2 shared

Labs

• Atmospheric Sciences Research LabPI