The Latent Heating Feedback on the Mid‐Latitude Circulation
Geophysical Research Letters Wiley 52:18 (2025) e2025GL116437
Abstract:
Plain Language Summary: Midlatitude storms transport water vapor poleward and upward. When ascending, the air cools, causing the vapor to condense, releasing latent heat. The latent heating boosts the ascent in which it occurs and amplifies the storms originally responsible for the heating. This circular chain of events couples latent heating and storms in a nonlinear relationship we call the latent heating feedback. We simulate an atmosphere where latent heating is static and not a consequence of warm, moist air ascending. Comparing this to an atmosphere with realistic latent heating, we show that realistic latent heating leads to more intense storms traveling further poleward, especially west of North America and Europe. Simultaneously, the longitudinally averaged jet streams and storms respond by retracting toward the equator, leaving reduced westerlies and a double jet tendency over North America and Europe. Previous works tend to focus on the effect of latent heating on the average atmospheric state. Our work shows that this effect is only part of the story and that the latent heating effect on storms directly causes regional differences that climate models struggle with.Impact of Asian Summer Monsoon on the 2021 Pacific Northwest Heatwave: Can It? Did It?
Geophysical Research Letters Wiley 52:18 (2025) e2025GL117205
Abstract:
Plain Language Summary: The Pacific Northwest (PNW) experienced a record‐breaking heatwave during the summer of 2021, resulting in significant adverse effects on both human society and ecosystems. A heavy rainfall band was observed stretching from south China to south of Japan 1 week prior to the heatwave, fueling the debate over whether the monsoon activity contributed to this event. Our study found that while the monsoon activity typically has a cooling effect on the PNW's climate, in this particular year, it had a warming effect and thus contributed to this specific heatwave. This unusual warming effect was driven by a stronger and more northward‐shifted Pacific jet stream, which altered the extratropical response to the monsoon, resulting in an anticyclonic pattern over the PNW instead of the typical cyclonic response seen under average climatic conditions. Therefore, it is important to distinguish between the general question of whether monsoon can influence such events on average, and the specific question of whether it did in any specific case. We argue that when discussing the influence of large‐scale climate drivers on extremes, it is crucial to clearly state whether the focus is on the general potential for influence or on the specific role in a particular event.Robust impact of tropical Pacific SST trends on global and regional circulation in boreal winter
npj Climate and Atmospheric Science Nature Research 8:1 (2025) 315
Abstract:
Evidence has emerged of a discrepancy in tropical Pacific sea surface temperature (SST) trends over the satellite era, where most coupled climate models struggle to simulate the observed La Niña-like SST trends. Here we highlight wider implications of the tropical Pacific SST trend discrepancy for global circulation trends during boreal winter, using two complementary methods to constrain coupled model SST trends: conditioning near-term climate prediction (hindcast) simulations, and pacemaking coupled climate simulations. The robust circulation trend response to constraining the tropical Pacific SST trend resembles the interannual La Niña response. Constraining tropical Pacific SST robustly reduces tropical tropospheric warming, improving agreement with reanalyses, and moderately shifts the zonal-mean jets poleward. It also improves surface air temperature and precipitation trends in ENSO-sensitive regions, such as the Americas, South Asia, and southern Africa. Our results underline the importance of tropical Pacific SST for achieving confidence in multidecadal model projections.The representation of surface temperature trends in C3S seasonal forecast systems
Atmospheric Science Letters Wiley 26 (2025) e1316
Abstract:
We assess near-surface temperature and sea surface temperature trends in 8 seasonal forecast systems in the Copernicus Climate Change Service archive, over the common hindcast period (1993–2016). All but one of the systems show a faster warming of the global-mean, relative to observations in both boreal summer and winter seasons. On average, systems warm at 0.21K/decade and 0.22K/decade for winter and summer, respectively, compared to 0.17K/decade and 0.19K/decade for ERA5. In summer, forecast systems tend to show an excessive warming of the tropical Pacific, tropical Atlantic and southern mid-latitudes, which contributes to the difference in global warming rates compared to observations. In contrast, greater warming in the northern mid-latitudes contributes most to trend differences for winter. The faster warming of models over this period has important implications for seasonal forecasts of future global and regional temperature and suggests further work is required to understand this bias.
The impact of different haze types on the atmospheres and observations of hot Jupiters: 3D simulations of HD 189733b, HD 209458b, and WASP-39b
Monthly Notices of the Royal Astronomical Society, Volume 542, Issue 3, pp.1873–1900 (2025)
Abstract:
We present the results from the simulations of the atmospheres of hot-Jupiters HD 189733b, HD 209458b, and WASP-39b, assuming the presence of three different types of haze. Using a 3D general circulation model, the Unified Model, we capture the advection, settling, and radiative impact of Titan-, water-world-, and soot-like haze, with a particle radius of 1.5 nm. We show that the radiative impact of haze leads to drastic changes in the thermal structure and circulation in the atmosphere. We then show that in all our simulations, (1) the super-rotating jet largely determines the day-to-night haze distribution, (2) eddies drive the latitudinal haze distribution, and (3) the divergent and eddy component of the wind control the finer structure of the haze distribution. We further show that the stronger the absorption strength of the haze, the stronger the super-rotating jet, lesser the difference of the day-to-night haze distribution, and larger the transit depth in the synthetic transmission spectrum. We also demonstrate that the presence of such small hazes could result in a stronger haze opacity over the morning terminator in all three planets. This could lead to an observable terminator asymmetry in WASP-39b, with the morning terminator presenting a larger transit depth than the evening terminator. This work suggests that, although it might not be a typical detection feature for hot Jupiters, an observed increase in transit depth over the morning terminator across the ultraviolet and optical wavelength regime could serve as a strong indicator of the presence of haze.