The impact of ultraviolet heating and cooling on the dynamics and observability of lava planet atmospheres
Monthly Notices of the Royal Astronomical Society Oxford University Press 513:4 (2022) 6125-6133
Abstract:
Lava planets have non-global, condensible atmospheres similar to icy bodies within the Solar system. Because they depend on interior dynamics, studying the atmospheres of lava planets can lead to understanding unique geological processes driven by their extreme environment. Models of lava planet atmospheres have thus far focused on either radiative transfer or hydrodynamics. In this study, we couple the two processes by introducing ultraviolet (UV) and infrared (IR) radiation to a turbulent boundary layer model. We also test the effect of different vertical temperature profiles on atmospheric dynamics. Results from the model show that UV radiation affects the atmosphere much more than IR. UV heating and cooling work together to produce a horizontally isothermal atmosphere away from the substellar point regardless of the vertical temperature profile. We also find that stronger temperature inversions induce stronger winds and hence cool the atmosphere. Our simulated transmission spectra of the bound atmosphere show a strong SiO feature in the UV that would be challenging to observe in the planet’s transit spectrum due to the precision required. Our simulated emission spectra are more promising, with significant SiO spectral features at 4.5 and 9 μm that can be observed with the James Webb Space Telescope. Different vertical temperature profiles produce discernible dayside emission spectra, but not in the way one would expect.Revisiting mechanisms of the Mesoamerican Midsummer drought
Climate Dynamics Springer 60 (2022) 549-569
Abstract:
Observations show that the seasonal cycle of precipitation in parts of southern Mexico and Central America exhibits a bimodal signal, known as the Midsummer drought (MSD), but there is no consensus on which processes are most relevant for the two-peak structure of the rainy season. This paper evaluates three hypotheses that could explain the MSD: the SST cloud-radiative feedback, the solar declination angle and the Caribbean Low-Level Jet (CLLJ) moisture transport hypotheses. Model experiments produced by the Met Office Hadley Centre (MOHC) for CMIP6 as well as ERA5 reanalysis data are used to critically assess the predictions of each hypothesis. The simulations capture the double peak signal of precipitation well and reasonably simulate the spatial and temporal variations of the MSD and other relevant climate features such as the CLLJ. Evidence from our analysis suggests that the Eastern Pacific SSTs do not increase in late summer in ERA5 data and only slightly increase in the simulations. More importantly, the Eastern Pacific SST variability in ERA5 and in the model experiments cannot explain the differences in the seasonality of precipitation. The net shortwave radiation at the surface shows a two-peak seasonal cycle; however, this behaviour appears to result from a strong anti-correlation of the incoming shortwave and convective activity due to cloud radiative-effects. There was no evidence found by this study of a causal link in which absorption of shortwave energy forces precipitation variations, as suggested by the solar declination angle hypothesis. The moisture convergence, CLLJ and the precipitable water vapor variations best explain the characteristics of the observed and simulated MSD, particularly for the onset of the MSD. The diagnosed variations of moisture convergence, which are synchronous with the timing of the MSD, point to a dynamic mechanism in which the low-level inflow from the Caribbean is more important for the MSD than other radiative mechanisms.Mechanisms of influence of the semi-annual oscillation on stratospheric sudden warmings
Quarterly Journal of the Royal Meteorological Society Wiley 148:774 (2022) 1223-1241
Abstract:
The influence of the Semi-Annual Oscillation (SAO) on the timing and evolution of major sudden stratospheric warmings (SSWs) is examined using the 2008/9 SSW as the primary case study. When the zonal winds in both the troposphere and the SAO region of the equatorial upper stratosphere / lower mesosphere are relaxed towards reanalysis fields in the UK Met Office Unified Model a remarkably accurate representation of the January 2009 SSW is achieved. The accurate timing of the SSW is determined by the SAO zonal wind relaxation. The westerly to easterly phase transition of the SAO in the lower mesosphere (0.1-0.5 hPa) is found to be a key factor for this influence. It defines an initial conical-shaped vortex that determines the upward propagation of wave activity and subsequent evolution of wave mean-flow interaction. Internal transient wave reflection in the subtropics and associated wave-induced acceleration of the mean-flow is found to be an important component, strengthening the vortex and thus delaying the onset of the SSW. The sensitivity of SSW timing to the equatorial westerly winds in the lower mesosphere is further explored in the context of all major SSWs during the 1979-2018 period. The timing of SSWs is found to be significantly correlated with the timing of the equinoctial westerly-to easterly phase transition at 0.3 hPa in early winter (r = 0.79). This relationship is discussed in the context of the more widely recognised influence of the quasi-biennial oscillation (QBO). These results suggest that accurate simulation of the timing of SAO phase transitions, as well as knowledge of the QBO phase, is likely to provide additional and extended Northern Hemisphere winter-time seasonal forecast skill.Plant power: Burning biomass instead of coal can help fight climate change—but only if done right
Bulletin of the Atomic Scientists Taylor & Francis 78:3 (2022) 125-127
The impact of the QBO on the region of the tropical tropopause in QBOi models: Present-day simulations
Quarterly Journal of the Royal Meteorological Society Wiley 148:745 (2022) 1945-1964