Insights from Idealized Modelling into the Quasi-Biennial Oscillation 

2026-03-13

Most climate models that simulate the Quasi-Biennial Oscillation (QBO) substantially underestimate tropical zonal wind amplitudes in the lower stratosphere, which limits their ability to represent global QBO teleconnections. To investigate the causes of this long-standing bias and to identify the key requirements for simulating a realistic QBO, we use an idealized atmospheric model with simplified physics based on the GFDL dry spectral dynamical core. The model incorporates empirically derived latent heating from observed tropical precipitation to represent the effects of tropical convection on the generation of resolved waves that drive the QBO.We perform an extensive set of sensitivity experiments that systematically vary tropical heating, parameterized gravity wave drag, gravity wave drag strength and formulation, vertical resolution, and horizontal resolution. The results demonstrate that high vertical resolution (L80) is the most critical factor for reproducing realistic QBO amplitudes in the lower stratosphere. Parameterized gravity wave drag is also essential, as tropical heating alone is insufficient to sustain a robust QBO. In contrast, increasing horizontal resolution beyond moderate values provides little benefit, with simulations at T42 resolution already producing a reasonable QBO.

A thermodynamic bound on Hadley cell expansion

Research Square · 2026-04-16

Tropical Impacts From Polar Vortex Events

2025-03-15

Stratospheric sudden warmings and other polar vortex events have well-documented impacts on winter surface weather and climate over middle to high latitudes. However, the scientific understanding of the influence of the polar stratosphere on the tropics remains in its early stages. There are two primary pathways through which these influences can occur. In the first pathway, polar vortex events modulate the strength of the Brewer-Dobson circulation, affecting both the tropical stratosphere and troposphere. In the second pathway, the dynamical downward coupling from the stratosphere into the extratropical troposphere may also influence the tropical troposphere. To investigate the type and magnitude of tropical impacts from polar vortex events, we employ a composite analysis of ERA5 reanalysis data spanning from 1957 to 2024. Our findings reveal that stratosphere-related changes in the Brewer-Dobson circulation not only affect the tropics but also extend into the subtropics and extratropics of the opposite hemisphere. These impacts manifest in various variables, including tropical upwelling, the descent rate of the Quasi-Biennial-Oscillation, tropical stratospheric water vapor, the height and temperature of the tropical tropopause, and tropical column ozone. Furthermore, we find that stratospheric circulation events are associated with shifts in the poleward extent of the tropical Hadley cell. While these tropical changes are generally weaker compared to those observed at higher latitudes, they are nonetheless of comparable duration and statistically significant.

More intermittent mid-latitude precipitation accompanied extreme early Palaeogene warmth

Nature Geoscience · 2025-12-22

Data from: More intermittent mid-latitude precipitation accompanied extreme early Paleogene warmth

Open MIND · 2025-01-01

Warming is pushing the Earth system toward unfamiliar climate conditions, complicating predictions. Geological archives of past greenhouse climates provide essential tests for models under extreme forcing. We investigate how precipitation responded to extreme warmth during early Paleogene global warming events (66–47.8 million years ago) – a period considered a possible analogue for worst-case future scenarios. Here we compile global paleoclimate data and develop a multi-proxy approach that integrates sedimentary proxies - such as plant fossils, ancient soils and river deposits - providing constraints on global precipitation intermittency (seasonal and inter-annual variability) and intensity (rainfall rate). The data reveal wet or monsoonal polar regions, and aridity punctuated by intense rainfall at mid- and low-latitude continental interiors. This hydroclimate shift occurred 3 million years before and persisted 7 million years after the Paleocene-Eocene Thermal Maximum – the warmest period of the Cenozoic Era, suggesting that extreme warmth induces non-linearities in the hydrological cycle’s sensitivity to temperature increase. Polar humidity and mid-latitude aridity further indicate a departure from the expected wet-gets-wetter and dry-gets-drier response. Shifts towards aridity were decoupled from mean annual precipitation and driven by seasonal and interannual precipitation distribution, such as shorter wet season length and longer interannual rainfall recurrence interval. This highlights the importance of considering precipitation intermittency and intensity, as similar shifts may occur under future warming despite differences in boundary conditions.

Arctic Ozone Amplifies Stratospheric Circulation Extremes

Journal of Climate · 2025-04-18

Abstract Stratospheric ozone has long been suspected to drive interactions involving chemistry, radiation, and the circulation. However, the significance of these interactions, the underlying mechanisms, and the specific conditions that facilitate them remain poorly understood. In this study, we use a dry dynamical-core model with a simplified linear ozone scheme and a shortwave radiation parameterization to investigate these interactions. Our analysis, based on two long control simulations with either interactive or prescribed ozone, reveals that interactive ozone increases the persistence and interannual variability of the stratospheric circulation during northern spring, a period with sufficient solar radiation over the northern polar cap. This effect is closely linked to late-winter extreme stratospheric circulation events, such as stratospheric sudden warmings (SSWs) and vortex intensifications (VIs). While interactive ozone does not alter the frequency of these events, the ozone perturbations induced by the circulation amplify the associated temperature and wind anomalies. Specifically, late-winter VIs are followed by a colder and more persistent polar vortex in spring when interactive ozone is used, compared to fixed ozone. This results in a 5-day delay in the breakdown date of the vortex and a more positive North Atlantic Oscillation at the surface. Although interactive ozone also amplifies perturbations following SSWs, these effects are less pronounced than those observed for VIs. Our findings contribute to a growing body of evidence highlighting the importance of ozone–dynamics interactions for simulating the stratospheric circulation, its variability, and its surface impacts.

Arctic Ozone Amplifies Stratospheric Circulation Extremes

Research Square · 2024-12-13

A simple framework for likely climate projections applied to tropical width

Climate Dynamics · 2024-07-13 · 4 citations

Proxy-Informed Model Estimates of Early Paleogene Climate

2024-10-30

As global temperatures approach levels unprecedented in human history, past warm periods offer insights into climate variations associated with increasing greenhouse gas concentrations. The Early Paleogene (65-49 million years ago) is a prime example of a warmer climate state, with average temperatures 10 to 19 K higher than today. However, our understanding of this period is limited by sparse proxy data and uncertainties in key model parameters, preventing a comprehensive analysis of its climate. In this study we use a new compilation of temperature proxies to select the least biased simulations from the Deep-Time model intercomparison project for each of six Early Paleogene time periods. These ensembles align well with proxy temperature and precipitation data across all six periods of the Early Paleogene. This method also provides an independent estimation of CO2 concentrations, suggesting that Early Paleogene CO2 levels were around 600-1200 ppm, except for the warmest periods, the Paleocene Eocene Thermal Maximum (PETM) and Early Eocene Climatic Optimum where CO2 concentrations were 1100-1800 and 900-1500 ppm, respectively. The ensembles suggest temperatures in high-latitude regions increased by up to 13 K during the PETM hyperthermal, while tropical temperatures rose by approximately 1 K, indicating substantial polar amplification during the nearly ice-free Early Paleogene. Precipitation increased almost everywhere with warming, at a global mean rate of 2% per Kelvin of global warming, matching theorized and modeled estimates from the modern climate. Additionally, precipitation changes suggest a poleward shift in global atmospheric circulation with warming, aligning with theories of modern climate change.

Replicating the Hadley cell edge and subtropical jet latitude disconnect in idealized atmospheric models

Weather and Climate Dynamics · 2024-02-20 · 4 citations

Abstract. Recent work has shown that variability in the subtropical jet's (STJ) latitude, ϕSTJ, is not coupled to that of the Hadley cell (HC) edge, ϕHC, but the robustness of this disconnect has not been examined in detail. Here, we use meteorological reanalysis products, comprehensive climate models, and an idealized atmospheric model to determine the necessary processes for a disconnect between ϕHC and ϕSTJ in the Northern Hemisphere's December–January–February season. We find that a decoupling can occur in a dry general circulation model, indicating that large-scale dynamical processes are sufficient to reproduce the metrics' relationship. It is therefore not reliant on explicit variability in the zonal structure, convection, or radiation. Rather, the disconnect requires a sufficiently realistic climatological basic state. Further, we confirm that the robust disconnect between ϕSTJ and ϕHC across the model hierarchy reveals their differing sensitivities to midlatitude eddy momentum fluxes; ϕHC is consistently coupled to the latitude of maximum eddy momentum flux, but ϕSTJ is not.