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Exoplanetary Ionospheric Temperatures on the Edge of Airlessness

(2025)

Authors:

Richard D Chatterjee, Sarah Blumenthal, Raymond T Pierrehumbert

Abstract:

The pattern of airy and airless rocky planets presently being uncovered by JWST is a record of what happens when ionospheres are pushed to their limits by their host stars. Orbiting as close to a red dwarf host as the Parker Probe is to the Sun, a massive rocky planet could harbour liquid water oceans beneath an ionosphere several times hotter than its star’s effective temperature, exhibiting spectacular airglow and aurora. Not only is this a distinct and observable possibility, but planets of this kind may make up a significant fraction of habitable worlds.What maximum temperature can a tightly bound ionosphere, composed primarily of carbon, nitrogen, and oxygen atoms, reach before escaping into space as a hydrodynamic wind? This question lies at the crux of the 500-hour Rocky Worlds DDT Program and the guiding hypothesis of a universal cosmic shoreline.Locally, the terminal temperatures of these extreme ionospheres are determined by heating from XUV photons emitted by the star’s corona and cooling through collisional excitation of atoms that emit visible and infrared photons. Globally, the thermal structure is determined by photochemistry, fluid dynamics, and electromagnetic interactions. Additionally, stellar cycle variation of ionospheric conditions is likely key to atmospheric evolution. In this talk, we will discuss the key knowns and unknowns in predicting the “edge of airlessness” for the population of rocky exoplanets within the observational reach of the James Webb Space Telescope.
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Verification of weather variables linked to Dengue incidence inthe sub‐seasonal scale in Vietnam

(2025)

Authors:

Iago Perez, Sarah Sparrow, Antje Weisheimer, Matthew Wright, Lucy Main

Abstract:

Dengue fever outbreaks impose a severe healthcare burden in Vietnam, therefore the development of an early Dengue warning system is key to improve public health planning and mitigate the future burden produced by this disease. This study assessed the ECMWF ensemble re-forecast skill for relative humidity, temperature and precipitation, which are key factors for vector-borne disease transmission in Vietnam between 1-4 weeks in advance. We focused the analysis on the rainy season (May-October) using ERA5 reanalysis as a reference dataset. Re-forecast data was pre-processed using a quantile mapping technique to reduce the bias between re-forecast and observations. Results showed that corrected re-forecasts of weekly mean temperature, relative humidity and accumulated precipitation are skilful up to 2-3 weeks in advance and rank histograms verified the forecast reliability. Nonetheless the model is less skillful for the region of South Vietnam and seems to struggle at predicting extremely high/low values of temperature, relative humidity and precipitation. Results from this study demonstrate that ECMWF ensemble forecasts are suitable to use as inputs for a dengue early warning system up to 14-21 days in advance
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What controls the bulk iron content of rocky planets?

(2025)

Authors:

Claire Guimond, Oliver Shorttle, Philipp Baumeister, Raymond Pierrehumbert

Abstract:

Iron is a powerful element shaping rocky planets. The bulk iron content of a planet exerts a first-order control on its interior structure, of fundamental importance to geodynamic processes. Across the rocky planets and dwarf planets in the solar system, bulk iron contents vary considerably, appearing to correlate with orbital distance, and possibly the Sun’s magnetic field strength (McDonough & Yoshizaki, 2021). Potentially-rocky exoplanets show an even greater spread in bulk density and hence inferred bulk iron content. Such exoplanet censuses have begun to give us access to cosmic-scale statistics. We build on McDonough & Yoshizaki (2021) to present a tentative, positive trend between rocky exoplanets’ iron contents and the energy they receive from their host star (instellation). Previous studies have searched for such a trend in iron content with other factors; in particular, with host star iron abundance, as such a link would be evidence for a planet-star compositional connection. If planet bulk iron content is also affected by disk processes, then any other trends would become more complicated to interpret. We use our results to address exoplanet bulk compositional diversity, including the formation of super-Mercuries, and discuss potential implications of high iron contents on broader planet evolution.McDonough, W. F., & Yoshizaki, T. (2021). Terrestrial planet compositions controlled by accretion disk magnetic field. Progress in Earth and Planetary Science, 8, 39.
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 Investigating the sensitivity of 20th century seasonal hindcasts to tropospheric aerosol forcing

(2025)

Authors:

Matthew Wright, Antje Weisheimer, Tim Woollings, Retish Senan, Timothy Stockdale

Abstract:

Previous studies have identified multi-decadal variations in the skill of winter seasonal forecasts of large-scale climate indices, including ENSO, the PNA, and NAO. Forecast skill is significantly lower in the middle of the 20th century (1940—1960) than at the start or end of the century. We hypothesise that tropospheric aerosol forcing, which is spatially and temporally heterogeneous and poorly constrained in the hindcasts used in previous studies, contributes to this low skill mid-century period.This study assesses the sensitivity of ECMWF’s state-of-the-art seasonal forecasting model to tropospheric aerosol forcing, using a newly developed aerosol forcing dataset based on CEDS emissions data. We analyse DJF hindcasts initialised every November from 1925—2010, each with 21 ensemble members. For each year, we run hindcasts with ‘best guess’, doubled, and halved aerosol forcing (perturbing both anthropogenic and natural aerosols). All experiments exhibit similar multi-decadal variability in skill for large-scale climate indices. Aerosol forcing has no significant impact on forecast skill but some impacts on mean biases, suggesting other factors drive the mid-century skill minimum.Aerosol forcing has large regional impacts. Increasing aerosol forcing leads to cooler 2m temperature and SSTs globally, with amplified cooling in regions with large aerosol forcings, such as northern India and North Africa. Dynamical responses include an ‘anti-monsoon’ circulation over Africa, with a weakening of the trade winds and Atlantic Walker circulation, and local southwards shift of the ITCZ. The magnitude of the response increases when ocean initial conditions are perturbed to represent the cumulative impact of aerosol forcing, suggesting that coupling enhances the atmospheric response.These results highlight the model’s sensitivity to tropospheric aerosols, with large differences in bias and mean state after four months, despite limited impact on skill. The circulation changes over Africa warrant further investigation, with implications for future aerosol scenarios. Planned experiments will explore the impact in summer and quantify the timescale of the response to aerosols.
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Advancing Organized Convection Representation in the Unified Model: Implementing and Enhancing Multiscale Coherent Structure Parameterization

(2025)

Authors:

Zhixiao Zhang, Hannah Christensen, Mark Muetzelfeldt, Tim Woollings, Robert Stephen Plant, Alison Stirling, Michael Whitall, Mitchell W Moncrieff, Chih-Chieh Chen, Zhe Feng
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