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A sensitive (1σrms ≤ 3 mK; 2 MHz resolution) 1 mm spectral survey (214.5–285.5 GHz) of the envelope of the oxygen-rich supergiant star NML Cygni (NML Cyg) has been conducted using the 10 m Submillimeter Telescope of the Arizona Radio Observatory. These data represent the first spectral line survey of NML Cyg and are complementary to a previous 1 mm survey of the envelope of a similar hypergiant, VY Canis Majoris (VY CMa). The complete NML Cyg data set is presented here. In the survey, 104 emission lines were observed, arising from 17 different molecules and 4 unidentified features. Many of the observed features have complex line profiles, arising from asymmetric outflows characteristic of hypergiant stars. While most of the lines in the survey arise from SiO, SO, SO₂, and SiS, CO had the strongest emission. Five other C-bearing species are identified in the survey (HCN, CN, HCO⁺, CS, and HNC), demonstrating an active carbon chemistry despite the O-rich environment. Moreover, NS was observed, but not NO, although favorable transitions of both molecules lie in the surveyed region. Sulfur chemistry appears to be prominent in NML Cyg and plays an important role in the collimated outflows. The refractory species observed, NaCl and AlO, have narrow emission lines, indicating that these molecules do not reach the terminal expansion velocity. NaCl and AlO likely condense into dust grains at r < 50R_*. From NaCl, the chlorine isotope ratio was determined to be³⁵Cl/³⁷Cl = 3.85 ± 0.30.

 

Subseasonal weather prediction can reduce economic disruption and loss of life, especially during “windows of opportunity” when noteworthy events in the Earth system are followed by characteristic weather patterns. Sudden stratospheric warmings (SSWs), breakdowns of the winter stratospheric polar vortex, are one such event. They often precede warm temperatures in Northern Canada and cold, stormy weather throughout Europe and the United States - including the most recent SSW on January 5th, 2021. Here we assess the drivers of surface weather in the weeks following the SSW through initial condition “scrambling” experiments using the real-time CESM2(WACCM6) Earth system prediction framework. We find that the SSW itself had a limited impact, and that stratospheric polar vortex stretching and wave reflection had no discernible contribution to the record cold in North America in February. Instead, the tropospheric circulation and bidirectional coupling between the troposphere and stratosphere were dominant contributors to variability.

 

Previous work identified an anthropogenic fingerprint pattern in 𝑇AC (𝑥, 𝑡), the amplitude of the seasonal cycle of mid- to upper tropospheric temperature (TMT), but did not explicitly consider whether fingerprint identification in satellite 𝑇AC(𝑥,𝑡) data could have been influenced by real-world multidecadal internal variability (MIV). We address this question here using large ensembles (LEs) performed with five climate models. LEs provide many different sequences of internal variability noise superimposed on an underlying forced signal. Despite differences in historical external forcings, climate sensitivity, and MIV properties of the five models, their 𝑇AC (𝑥, 𝑡) fingerprints are similar and statistically identifiable in 239 of the 240 LE realizations of historical climate change. Comparing simulated and observed variability spectra reveals that consistent fingerprint identification is unlikely to be biased by model underestimates of observed MIV. Even in the presence of large (factor of 3-4) inter-model and inter-realization differences in the amplitude of MIV, the anthropogenic fingerprints of seasonal cycle changes are robustly identifiable in models and satellite data. This is primarily due to the fact that the distinctive, global-scale fingerprint patterns are spatially dissimilar to the smaller-scale patterns of internal 𝑇AC(𝑥,𝑡) variability associated with the Atlantic Multidecadal Oscillation and the El Niño~Southern Oscillation. The robustness of the seasonal cycle D&A results shown here, taken together with the evidence fromidealized aquaplanet simulations, suggest that basic physical processes are dictating a common pattern of forced𝑇AC(𝑥,𝑡) changes in observations and in the five LEs. The key processes involved include GHG-induced expansion of the tropics, lapse-rate changes, land surface drying, and sea ice decrease. 

The predictability of the middle atmosphere during major sudden stratospheric warmings (SSWs) is investigated based on subseasonal hindcasts in the Community Earth System Model, version 2 with the Whole Atmosphere Community Climate Model as its atmospheric component (CESM2[WACCM6]). The CESM2(WACCM6) hindcasts allow for the first comprehensive investigation into the predictability of the mesosphere and lower thermosphere (MLT) during SSWs. Analysis of 14 major SSWs demonstrates that CESM2(WACCM6) hindcasts initialized5–15 days prior to the SSW onset are able to predict the timing of the SSW, though they underestimate the strength of the SSW. Aspects of the MLT variability, such as the mesosphere cooling and enhanced semidiurnal tide, are found to be well predicted. The demonstrated ability to predict MLT variability during SSWs indicates the potential for improved multi‐day space weather forecasting. Improved space weather forecasting may be achieved by using whole atmosphere models that can predict the MLT variability that drives ionosphere‐thermosphere variability during SSWs.

 

Plants moved onto land ∼450 million years ago and faced their biggest challenge: living in a dry environment. Over the millennia plants have become masters of regulating water flow and the toolkit they have developed has been co-opted to effect rapid movements. Since plants are rooted, these fast movements are used to disperse reproductive propagules including spores, pollen, and seeds. We compare five plants to demonstrate three ways, used alone or in combination, that water powers rapid movements: the direct capture of the kinetic energy of a falling raindrop propels gemmae from the splash cups of the liverwort, Marchantia; the loss of water powers the explosive dispersal of the spores of Sphagnum moss; the alternate loss and gain of water in the bilayer of the elaters of Equisetum drive the walk, jump, and glide of spores; the gain of water in the inner layer of the arils of Oxalis drive the eversion of the aril that jettisons seeds from the capsule; and the buildup of turgor pressure in the petals and stamens of bunchberry dogwood (Cornus canadensis) explosively propels pollen. Each method is accompanied by morphological features, which facilitate water movement as a power source. The urn shaped splash cups of Marchantia allow dispersal of gemmae by multiple splashes. The air gun design of Sphagnum capsules results in a symmetrical impulse creating a vortex ring of spores. The elaters of Equisetum can unfurl while they are dropping from the plant, so that they capture updrafts and glide to new sites. The arils of Oxalis are designed like miniature toy “poppers.” Finally, in bunchberry, the softening of stamen filament tissue where it attaches to the anther allows them to function as miniature hinged catapults or trebuchets.

 

An overview of the Community Earth System Model Version 2 (CESM2) is provided, including a discussion of the challenges encountered during its development and how they were addressed. In addition, an evaluation of a pair of CESM2 long preindustrial control and historical ensemble simulations is presented. These simulations were performed using the nominal 1° horizontal resolution configuration of the coupled model with both the “low‐top” (40 km, with limited chemistry) and “high‐top” (130 km, with comprehensive chemistry) versions of the atmospheric component. CESM2 contains many substantial science and infrastructure improvements and new capabilities since its previous major release, CESM1, resulting in improved historical simulations in comparison to CESM1 and available observations. These include major reductions in low‐latitude precipitation and shortwave cloud forcing biases; better representation of the Madden‐Julian Oscillation; better El Niño‐Southern Oscillation‐related teleconnections; and a global land carbon accumulation trend that agrees well with observationally based estimates. Most tropospheric and surface features of the low‐ and high‐top simulations are very similar to each other, so these improvements are present in both configurations. CESM2 has an equilibrium climate sensitivity of 5.1–5.3 °C, larger than in CESM1, primarily due to a combination of relatively small changes to cloud microphysics and boundary layer parameters. In contrast, CESM2's transient climate response of 1.9–2.0 °C is comparable to that of CESM1. The model outputs from these and many other simulations are available to the research community, and they represent CESM2's contributions to the Coupled Model Intercomparison Project Phase 6.