About

John M. Peters is an Assistant Professor of Meteorology and Atmospheric Science at Penn State. He earned his Ph.D. in Atmospheric Science from Colorado State University in 2015, his M.S. in Mathematics from the University of Wisconsin-Milwaukee in 2012, and his B.S. in Mathematics from the same university in 2010. His research is centered on moist atmospheric convection, with a particular focus on stormy phenomena such as cumulus clouds and thunderstorms. He studies the inner workings of these weather systems through a combination of theory, computer simulations, and real-world observations. His work aims to contribute to improvements in weather and climate forecasting.

Research topics

• Geology
• Meteorology
• Physics
• Mechanics
• Atmospheric sciences
• Environmental science
• Climatology
• Materials science
• Geography

Selected publications

• A Unified Theory for the Global Thunderstorm Distribution and Land–Sea Contrast

  Geophysical Research Letters · 2026-01-01 · 1 citations

  articleOpen access1st authorCorresponding

  Abstract This article evaluates Entraining CAPE (ECAPE) as a thunderstorm proxy in climate studies using Global Precipitation Measurement satellite observations. ECAPE modifies traditional CAPE to account for the dependence of entrainment on the vertical wind shear, the lifted condensation level (LCL) height, and the properties of a cloud's surrounding atmosphere. ECAPE shows stronger pattern correlations with global regions of intense thunderstorms than previous metrics for updraft speed. In these regions, large CAPE, large shear, and high LCLs conspire to produce wide updrafts that are shielded from the negative effects of dry‐air entrainment. ECAPE more skillfully discriminates intense thunderstorms from their less intense counterparts than other metrics commonly used in climatology and climate change studies of thunderstorms. We provide evidence that the well‐known land‐sea contrast in thunderstorm intensity is a consequence of larger CAPE and higher LCL heights over land than over the ocean.

  PublisherDOI

• Comment on egusphere-2025-4495

  2026-02-19

  peer-reviewOpen access

  <strong class="journal-contentHeaderColor">Abstract.</strong> Downdrafts play an essential role in the feedback between convective clouds and their surrounding environment, and they must be properly accounted for in cumulus parameterizations (CPs). The mechanisms for downdraft formation are often debated in past literature and inconsistently represented in CPs. To address this uncertainty, we investigate the ring of descent surrounding cloudy updrafts known as a subsiding shell, a leading contributor to downdraft mass flux. We analyze two LES of deep convection in the Amazonian dry and wet season, using composite soundings from the Green Ocean Amazon Campaign. The dry and wet season soundings differ in their middle tropospheric relative humidity (RH), which facilitates an assessment of the influence of RH on shell strength. Kinetic energy budgets along trajectories reveal that shells acquire their descent from evaporatively driven negative effective buoyancy along cloud edge and downward oriented dynamic pressure accelerations associated with the toroidal circulations of updraft thermals. Consistent with observations, shell downdrafts were strongest in the dry season simulation. Contrary to hypotheses which attributed this difference to greater evaporative cooling, we find that dry season shell downdrafts associated with deep convection were stronger because of larger dynamic pressure accelerations in the dry season. However, when investigating cumulus congestus clouds, negative effective buoyancy accelerations become increasingly important relative to pressure accelerations. The stronger accelerations in deep convective shells were attributed to stronger dry season updrafts, and consequently more intense toroidal circulations within thermals. Our results provide a foundation of understanding for future improvement of downdraft representation in CPs.

  PublisherDOI

• Driving Mechanisms for Subsiding Shells in Simulations of Deep Moist Convection

  2025-09-30

  preprintOpen access

  Abstract. Downdrafts play an essential role in the feedback between convective clouds and their surrounding environment, and they must be properly accounted for in cumulus parameterizations (CPs). The mechanisms for downdraft formation are often debated in past literature and inconsistently represented in CPs. To address this uncertainty, we investigate the ring of descent surrounding cloudy updrafts known as a subsiding shell, a leading contributor to downdraft mass flux. We analyze two LES of deep convection in the Amazonian dry and wet season, using composite soundings from the Green Ocean Amazon Campaign. The dry and wet season soundings differ in their middle tropospheric relative humidity (RH), which facilitates an assessment of the influence of RH on shell strength. Kinetic energy budgets along trajectories reveal that shells acquire their descent from evaporatively driven negative effective buoyancy along cloud edge and downward oriented dynamic pressure accelerations associated with the toroidal circulations of updraft thermals. Consistent with observations, shell downdrafts were strongest in the dry season simulation. Contrary to hypotheses which attributed this difference to greater evaporative cooling, we find that dry season shell downdrafts associated with deep convection were stronger because of larger dynamic pressure accelerations in the dry season. However, when investigating cumulus congestus clouds, negative effective buoyancy accelerations become increasingly important relative to pressure accelerations. The stronger accelerations in deep convective shells were attributed to stronger dry season updrafts, and consequently more intense toroidal circulations within thermals. Our results provide a foundation of understanding for future improvement of downdraft representation in CPs.

  PublisherOA PDFDOI

• Effective Buoyancy in Squall Lines

  Journal of the Atmospheric Sciences · 2025-05-30

  article1st authorCorresponding

  Abstract Squall lines consist of a buoyancy discontinuity with positive buoyancy extending hundreds of kilometers behind their leading edge. Because of this structure, conceptual models for isolated deep convective updrafts, which have a comparatively limited horizontal extent, fail to explain squall-line thermodynamics. The present article addresses this knowledge gap by forming analytic solutions for effective buoyancy using simplified density distributions that mimic squall-line structure and by examining accompanying numerical simulations. It is shown with both analytical analysis and simulations that effective buoyancy along most squall-line updraft trajectories is less than half of the value predicted by parcel theory, implying that squall lines are fundamentally incapable of realizing all of their convective available potential energy as kinetic energy. This scaling factor is generally unaffected by the system’s horizontal extent, the width of the deep convective updrafts along the system’s leading edge, and the curvature of bowing segments. When the cold pool and low-level shear are close to balanced, there is an increased prevalence of “hot towers,” whose local buoyancy exceeds their immediate surroundings, allowing the effective buoyancy-to-buoyancy ratio along some trajectories to slightly exceed one-half. As the rearward slant of updrafts increases, the dilution of updraft buoyancy increases, the ratio of effective buoyancy to buoyancy decreases, and hot towers become less prevalent, leading to weaker updrafts. Dilution of updrafts, along with system slant and the associated reduction in effective buoyancy, is the primary control on updraft intensity. These results provide an underlying foundation for future theories that predict squall-line updraft speeds. Significance Statement Squall lines are organized clusters of thunderstorms that span hundreds of kilometers, producing prolific lightning, heavy rainfall, and damaging winds. Unlike isolated thunderstorms, their structure includes a wide area of buoyancy behind the leading edge, making traditional theories of storm updrafts insufficient to explain their behavior. This study addresses the aforementioned knowledge gap by using theory and computer simulations to improve our understanding of squall-line updrafts. The findings reveal that squall-line updrafts are inherently less efficient at converting environmental energy into updraft motion than isolated storms, with efficiency generally less than half of what conventional theory predicts. The study also shows how factors such as the balance between shear and buoyancy along the system outflow and updraft slant influence storm strength. These results lay the groundwork for improved understanding and forecasting of squall-line dynamics.

  PublisherDOI

• Environmental Drivers and Dynamics of Downdrafts in Simulations of Convection

  2025-03-14

  preprintOpen accessSenior author

  Downdrafts play an essential role in the feedback between deep convective clouds and their surrounding environment, and they must be properly accounted for in climate model parameterization schemes. Such downdrafts found near and in-cloud, such as subsiding shells and hydrometeor-loaded downdrafts, significantly contribute to downward mass flux in the lower and middle troposphere. However, environmental links to driving mechanisms and characteristics of downdrafts must be understood for proper implementation in parameterization schemes. Using CM1, simulations modeling convection were performed utilizing weakly-sheared dry and wet season composite soundings compiled during the Green Ocean Amazon Campaign, as well as similar thermodynamic soundings with a prescribed increase of vertical wind shear. The soundings in this study were adapted to isolate relative humidity and shear effects on convective downdrafts. All deep convective updrafts in the simulations that met a required vertical velocity threshold were analyzed, along with their near-cloud environments and associated downdrafts. Magnitude differences of subsidence in the matrix of environments encouraged a parcel trajectory analysis, which showed that downward accelerations were primarily driven by negative buoyancy accelerations and were aided by cloud-top pressure perturbations. Compared to other near-cloud downdrafts, subsiding shell accelerations relied heavily on strongly negative thermal buoyancy for downward accelerations but were also moderated by upward vertical perturbation pressure gradient accelerations away from cloud top, ultimately making them weaker than all other downdrafts. Future work aims to increase understanding of and improve mass transport processes found in near-cloud downdrafts and apply such understanding to climate model cumulus and convective parameterization schemes.

  PublisherDOI

• The U.S. DOE ARM User Facility Establishes a New Site for Studies of Land–Aerosol–Cloud Interactions in the Southeastern United States

  Bulletin of the American Meteorological Society · 2025-11-04

  article

  Abstract The U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) user facility has established a new site in the Bankhead National Forest (BNF) in northern Alabama that will gather data on how clouds, the land surface, and aerosols interact at a hierarchy of scales important to understanding and simulating the Earth system. Starting its operations in October 2024, the BNF site provides a multiyear opportunity for scientists to unravel complex land–atmosphere interactions. A suite of ground-based sensors, elevated tower-based instrumentation, and aerial facilities will enable scientists to investigate those interactions from within the canopy to the clouds. The southeastern United States was recommended by the DOE ARM and its collaborators in the broader community as an important region to address their common scientific questions, given the region’s abundant surface-forced convective clouds and mesoscale convective systems that pose ongoing challenges in Earth system models. The region is also home to significant terrain complexity and land-use heterogeneity that will unleash new understanding of anthropogenic and biogenic aerosol processes, boundary layer aerosol–cloud interactions, and the interactions between the terrestrial ecosystem and coupled aerosol–cloud–radiation processes.

  PublisherDOI

• What do large hail, tornado and severe thunderstorm wind environments have in common across continents?

  2025-08-08

  preprintOpen access

  Parameter studies for convective storm environments have historically focused on single continents. Here, we considered severe weather reports (hail, tornadoes, severe convective winds), lightning detection data and ERA5 reanalysis across four parts of the world: Europe, Australia, South America, and the United States. We analyzed convective parameters and vertical profiles of atmospheric quantities for severe and non-severe thunderstorms to better understand which environmental features share similarities among continents and reliably represent convective hazards. Thermodynamic parameters are the most useful proxies of hail and warm season severe winds, whereas kinematic parameters are the most robust predictors of storm severity, especially tornadoes, whose environments feature large contribution of low-level streamwise vorticity. Hail experiences weak near ground winds and the strongest bulk wind shear between 1–3 km while tornadoes and severe winds have the largest shear near ground. Larger hail and stronger tornadoes can be expected with increasing storm-relative winds, moisture fluxes, and mid-tropospheric ventilation (i.e. wind component perpendicular to inflow axis). Extending hodograph to its origin while calculating storm-relative helicity and streamwise vorticity improves tornado prediction, especially for shallow layers (0–100 m). Lifted parcel buoyancy in the hail growth layer (-10°C to -40°C) is important for assessing likelihood of hail. Using peak parcel buoyancy (instead of integrated) leads to more skilful predictions of hail and tornadoes, especially when entraining parcel calculation procedure is incorporated . We also note that some parameters are geographically dependent (e.g. lapse rates), and that parameters, which are good predictors for the occurrence of convective hazards, are typically not the best parameters of their intensity.

  PublisherDOI

• The Influence of Heterogeneous Surface Heating on Organized Vertical Motions within and above a Sheared, Unstable Atmospheric Boundary Layer

  Journal of the Atmospheric Sciences · 2025-07-10

  articleSenior author

  Abstract Large-eddy simulation (LES) runs are performed to understand the influence of a one-dimensional (1D) surface heating heterogeneity on organized vertical motions within and above the atmospheric boundary layer (ABL). Two knowledge gaps are of interest: (i) how updrafts develop in the low free troposphere and (ii) what parameters control updraft location and strength within the ABL? LES runs are performed for a sheared, unstable ABL driven by geostrophic winds of the same magnitude but in various directions relative to a 1D surface-heat-flux heterogeneity. Quasi-steady-state LES results are phase-averaged over time and the horizontal dimension perpendicular to the surface-heat-flux gradient to quantify secondary circulations. Regarding the first knowledge gap, the results show that organized vertical motions in the low free troposphere can be modeled as two-dimensional (2D), stationary gravity waves, whose amplitudes depend on ABL updraft strength and instability development within the free troposphere. For the second gap, the results show that organized updrafts within the ABL may form above warm surfaces or downwind of warm-to-cool transitions. These different locations are well explained by both the relative contributions of horizontal and vertical velocities to the phase-averaged vorticity fluctuations tied to secondary circulations, and the relative importance of horizontal advection and turbulent transport in the phase-averaged internal energy fluctuation equation. The main balances associated with each updraft location are used to propose empirical models of updraft strength, and it is shown that the presence of sufficiently strong organized vertical motions can potentially change parameters used by atmospheric models that do not resolve ABL turbulence. Significance Statement The purpose of this study is to better understand how heterogeneous surface heating affects updraft location and strength in the lowest kilometers of the atmosphere. We focus on horizontal heterogeneity scales comparable to the most frequently observed cloud size, a necessary step toward the parameterization of cloud shadow effects in weather and climate models. The results show that persistent updrafts may form above either warm or cool surfaces, with their location depending on the relative importance of terms in certain budget equations. Near-surface updrafts become stronger as the background mean wind becomes more perpendicular to the surface-heat-flux gradient, but their potential to influence clouds peaks when the background mean wind is neither parallel nor perpendicular to the surface-heat-flux gradient.

  PublisherDOI

• Coastal-Urban-Rural Atmospheric Gradient Experiment (CoURAGE) Science Plan

  2024-08-01 · 1 citations

  reportOpen access

  Understanding the mechanisms governing the urban atmospheric environment is critical for informing urban populations regarding the impacts of climate change and associated mitigation and adaptation measures. Earth system (climate and weather) models have not yet been adapted to provide accurate predictions of climate and weather variability within cities, nor do they provide well-tested representations of the impacts of urban systems on the atmospheric environment. These limitations are largely due to limited field data available for testing and development of these models. We will deploy the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) user facility’s first Mobile Facility (AMF1) to the mid-Atlantic region surrounding the city of Baltimore for the Coast-Urban-Rural Atmospheric Gradient Experiment (CoURAGE). This deployment will create a four-node regional atmospheric observatory network including Baltimore and its three primary surrounding environments – rural, urban, and bay. CoURAGE investigators will study the interactions among the Earth’s surface, the atmospheric boundary layer, aerosols and atmospheric composition, clouds, radiation, and precipitation at each site, and examine how the spatial gradients across the region interact to create the climate conditions in Baltimore. This study will determine the degree to which Baltimore’s atmospheric environment depends on interactive feedbacks in the atmospheric system and the degree to which conditions in Baltimore depend on the surrounding environment. Some topics of interest include how urban land management exacerbates heat waves, the impact of regional mesoscale winds (nocturnal jet, bay breeze) on urban air pollution and cloud cover, and the impact of the urban heat island and aerosol production on heavy precipitation events. Understanding this integrated coast-urban-rural system quantitatively and with good accuracy and precision is critical to informing climate adaptation and mitigation efforts in the city of Baltimore. The understanding gained should be applicable to many similar coastal, mid-latitude urban centers. Another important objective of CoURAGE is to improve the representation of the climate of coastal cities in Earth systems models (ESMs). CoURAGE investigators will use the observations to test current ESMs, identify weaknesses and work towards improved simulations of this complex environment. The ARM core facility will be deployed in the city of Baltimore, complementing the Baltimore Social-Environmental Collaborative (BSEC), a DOE urban integrated field laboratory (UIFL). Ancillary sites will be deployed to rural Maryland northwest of Baltimore, and to the southern end of Kent Island within Chesapeake Bay. The fourth node will be a long-term atmospheric observatory operated in Beltsville, Maryland by Howard University and the Maryland Department of the Environment. Measurements will be conducted for one year, starting in December of 2024. There will be two intensive operational periods (IOPs), one in summer and one in winter, when the ancillary sites will be enhanced with additional balloon launches, tethered balloon system (TBS) operation, and added atmospheric composition measurements.

  PublisherOA PDFDOI

• Cumulonimbus Clouds Convert a Smaller Fraction of CAPE into Kinetic Energy in a Warmer Atmosphere

  Journal of the Atmospheric Sciences · 2024-09-09 · 3 citations

  articleOpen access1st authorCorresponding

  Abstract This study investigates how entrainment’s diluting effect on cumulonimbus updraft buoyancy is affected by the temperature of the troposphere, which is expected to increase by the end of the century. A parcel model framework is constructed that allows for independent variations in the temperature ( T ), the entrainment rate ε , the free-tropospheric relative humidity (RH), and the convective available potential energy (CAPE). Using this framework, dilution of buoyancy is evaluated with T and RH independently varied and with CAPE either held constant or increased with temperature. When CAPE is held constant, buoyancy decreases as T increases, with parcels in warmer environments realizing substantially smaller fractions of their CAPE as kinetic energy (KE). This occurs because the increased moisture difference between an updraft and its surroundings at warmer temperatures drives greater updraft dilution. Similar results are found in midlatitude and tropical conditions when CAPE is increased with temperature. With the expected 6%–7% increase in CAPE per kelvin of warming, KE only increases at 2%–4% K −1 in narrow updrafts but tracks more closely with CAPE at 4%–6% in wider updrafts. Interestingly, the rate of increase in the KE with T becomes larger than that of CAPE when the later quantity increases at more than 10% K −1 . These findings emphasize the importance of considering entrainment in studies of moist convection’s response to climate change, as the entrainment-driven dilution of buoyancy may partially counteract the influence of increases in CAPE on updraft intensity. Significance Statement Cumulonimbus clouds mix air with their surrounding environment through a process called entrainment, which controls how efficiently environmental energy is converted into upward speed in thunderstorm updrafts. Our research shows that warmer temperatures will exacerbate the moisture difference between cumulonimbus updrafts and their surroundings, leading to greater mixing and less efficient conversion of environmental energy into updraft speeds. This effect should be considered in future research that investigates how climate change will affect cumulonimbus clouds.

  PublisherOA PDFDOI

Recent grants

• AGS-PRF: Daytime to Nocturnal Convective Transition in the Central United States

  NSF · $127k · 2015–2017

• Statistical Methods for Environmental Genetic Research

  NIH · $42.9M · 2011–2014

• Improving Our Understanding of Pressure Perturbations in Cumulus Convection

  NSF · $300k · 2019–2022

Frequent coauthors

• Hugh Morrison

  NSF National Center for Atmospheric Research

  44 shared

• Rob McConnell

  University of Southern California

  22 shared

• Walter M. Hannah

  20 shared

• Kiros Berhane

  Columbia University

  20 shared

• Fred Lurmann

  Sonoma Technology (United States)

  15 shared

• Jake P. Mulholland

  University of North Dakota

  13 shared

• Christopher J. Nowotarski

  Texas A&M University

  12 shared

• Edward L. Avol

  University of Southern California

  11 shared

Awards & honors

• Alumni Society Award