Learning from weather and climate science to prepare for a future pandemic

Established pandemic models have yielded mixed results to track and forecast the SARS-CoV-2 pandemic. To prepare for future outbreaks, the disease-modeling community can improve their modeling capabilities by learning from the methods and insights from another arena where accurate modeling is paramount: the weather and climate research field. To prepare for future outbreaks, the disease-modeling community should draw on the methods and insights of the weather and climate research field. Image credit: Shutterstock/NASA Images. We argue that these improvements fall into four categories: model development, international comparisons, data exchange, and risk communication. A proper quantification of uncertainties in observations and models—including model assumptions, tail risks, and appropriate communication using probabilistic, Bayesian-based approaches—did not receive enough attention during the pandemic. Standardized testing and international comparison of model results is routine in climate modeling. No equivalent currently exists for pandemic models. Sharing of data is urgently needed. The homogenized real-time international data exchange, as organized by the World Meteorological Organization (WMO) since the 1960s, can serve as a role model for a global (privacy-preserving) data exchange by the World Health Organization. Lastly, researchers can look to climate change and high-impact weather forecasting to glean lessons about risk communication and the role of science in decision-making, in order to avoid common pitfalls and guide communication. Each of the four improvements is detailed here.publishedVersio

Moisture transport in mid-latitude cyclones

We discuss how synoptic-scale variability controls the transport of atmospheric water vapour by mid-latitude cyclones. Idealised simulations are used to investigate quantitatively what factors determine the magnitude of cyclone moisture transport. It is demonstrated that large-scale ascent on the warmconveyor belt and shallow cumulus convection are equally important for ventilating moisture from the boundary layer into the free troposphere, and that ventilated moisture can be transported large distances eastwards and polewards by the cyclone, before being returned to the surface as precipitation. The initial relative humidity is shown to have little affect on the ability of the cyclone to transport moisture, whilst the absolute temperature and meridional temperature gradient provide much stronger controls. Scaling arguments are presented to quantify the dependence of moisture transport on large-scale and boundary-layer parameters. It is shown that ventilation by shallow convection and warm-conveyor belt advection vary in the same way with changes to large-scale parameters. However, shallow convective ventilation has a much stronger dependence on boundary-layer parameters than warm-conveyor belt ventilation

Disentangling different moisture transport pathways over the eastern subtropical North Atlantic using multi-platform isotope observations and high-resolution numerical modelling

Due to its dryness, the subtropical free troposphere plays a critical role in the radiative balance of the Earth’s climate system. But the complex interactions of the dynamical and physical processes controlling the variability in the moisture budget of this sensitive region of the subtropical atmosphere are still not fully understood. Stable water isotopes can provide important information about several of the latter processes, namely subsidence drying, turbulent mixing, dry and moist convective moistening. In this study, we use high-resolution simulations of the isotope-enabled version of the regional weather and climate prediction model of the Consortium for Small-Scale Modelling (COSMO$_{iso}$) to investigate predominant moisture transport pathways in the Canary Islands region in the eastern subtropical North Atlantic. Comparison of the simulated isotope signals with multi-platform isotope observations (aircraft-based in situ measurements, ground-based and space-based remote sensing observations) from a field campaign in summer 2013 shows that COSMO$_{iso}$ can reproduce the observed variability of stable water vapour isotopes on time scales of hours to days, and thus allows studying the mechanisms that control the subtropical free-tropospheric humidity. Changes of isotopic signals along backward trajectories from the Canary Islands region reveal the physical processes behind the short-term isotope variability. We identify four predominant moisture transport pathways of mid-tropospheric air, each with distinct isotopic signatures: (1) Air parcels originating from the convective boundary layer of the Saharan heat low (SHL). These are characterised by a homogenous isotopic composition with a particularly high δD (median mid-tropospheric δD = −122 ‰), which results from dry convective mixing of low-level moisture of diverse origin advected into the SHL. (2) Air parcels originating from the free troposphere above the SHL. Although experiencing the largest changes in humidity and δD during their subsidence over West Africa, these air parcels typically have lower δD values (median δD = −148 ‰) than air parcels originating from the boundary layer of the SHL. (3) Air parcels originating from outside the SHL region, typically descending from tropical upper levels south of the SHL, which are often affected by moist convective injections from mesoscale convective systems in the Sahel. Their isotopic composition is much less enriched in heavy isotopes (median δD = −175 ‰) than those from the SHL region. (4) Air parcels subsiding from the upper-level extratropical North Atlantic. This pathway leads to the driest and most depleted conditions (median δD = −255 ‰) in the middle troposphere near the Canary Islands. The alternation of these transport pathways explains to a large degree the observed high variability in humidity and δD on synoptic time scales. We further show that the four different transport pathways are related to specific large scale-flow conditions. In particular, distinct differences in the location of the North African mid-level anticyclone and of extratropical Rossby wave patterns occur between the four transport pathways. Overall, this study demonstrates that the adopted Lagrangian isotope perspective enhances our understanding of air mass transport and mixing and offers a sound interpretation of the free-tropospheric variability of specific humidity and isotope composition on time scales of hours to days in contrasting atmospheric conditions over the eastern subtropical North Atlantic

Un campus en mouvement : Les pratiques de mobilité des étudiant-e-s et du personnel de l'Université de Lausanne

Les universités génèrent d’importants flux de mobilité et la gestion des transports constitue un défi majeur pour leur fonctionnement. Cette recherche aborde cette problématique dans le cas de l’Université de Lausanne. Dans un premier temps, l’étude porte sur l’évolution du campus et de son accessibilité. Elle montre comment ce site suburbain a été relié au reste de l’agglomération et aborde les mesures prises pour réguler la mobilité. Deuxièmement, elle s’intéresse à la demande, soit aux choix modaux des 18’000 personnes qui travaillent et étudient à l’Université de Lausanne. Des enquêtes réalisées chaque année depuis 2005 permettent de mesurer les pratiques de mobilité et les différences au sein de la communauté universitaire. En conclusion sont esquissées les tendances qui influenceront à terme les flux de mobilité à destination du campus

Lagrangian formation pathways of moist anomalies in the trade-wind region during the dry season: two case studies from EUREC4A

Shallow clouds in the trade-wind region over the North Atlantic contribute substantially to the global radiative budget. In the vicinity of the Caribbean island of Barbados, they appear in different mesoscale organization patterns with distinct net cloud radiative effects (CREs). Cloud formation processes in this region are typically controlled by the prevailing large-scale subsidence. However, occasionally weather systems from remote origin cause significant disturbances. This study investigates the complex cloud-circulation interactions during the field campaign EUREC4A (Elucidate the Couplings Between Clouds, Convection and Circulation) from 16 January to 20 February 2020, using a combination of Eulerian and Lagrangian diagnostics. Based on observations and ERA5 reanalyses, we identify the relevant processes and characterize the formation pathways of two moist anomalies above the Barbados Cloud Observatory (BCO), one in the lower troposphere (~ 1000-650 hPa) and one in the middle troposphere (~ 650-300 hPa). These moist anomalies are associated with strongly negative CRE values and with contrasting long-range transport processes from the extratropics and the tropics, respectively. The first case study about the low-level moist anomaly is characterized by an unusually thick cloud layer, high precipitation totals, and a strongly negative CRE. The formation of the low-level moist anomaly is connected to an extratropical dry intrusion (EDI) that interacts with a trailing cold front. A quasi-climatological (2010-2020) analysis reveals that EDIs lead to different conditions at the BCO depending on how they interact with the associated trailing cold front. Based on this climatology, we discuss the relevance of the strong large-scale forcing by EDIs for the low-cloud patterns near the BCO and the related CRE. The second case study about the mid-tropospheric moist anomaly is associated with an extended and persistent mixed-phase shelf cloud and the lowest daily CRE value observed during the campaign. The formation of the mid-level moist anomaly is linked to "tropical mid-level detrainment"(TMD), which refers to detrainment from tropical deep convection near the melting layer. The quasi-climatological analysis shows that TMDs consistently lead to mid-tropospheric moist anomalies over the BCO and that the detrainment height controls the magnitude of the anomaly. However, no systematic relationship was found between the amplitude of this mid-tropospheric moist anomaly and the CRE at the BCO. This is most likely due to the modulation of the CRE by above and below lying clouds and the fact that we used daily mean CREs, thereby ignoring the impact of the timing of the synoptic anomaly with respect to the daily cycle. Overall, this study reveals the important impact of the long-range moisture transport, driven by dynamical processes either in the extratropics or the tropics, on the variability of the vertical structure of moisture and clouds, and on the resulting CRE in the North Atlantic winter trades

A route to systematic error in forecasts of Rossby waves

Recent work has shown that both the amplitude of upper-level Rossby waves and the tropopause sharpness decrease with forecast lead time for several days in some operational weather forecast systems. In this contribution, the evolution of error growth in a case study of this forecast error type is diagnosed through analysis of operational forecasts and hindcast simulations. Potential vorticity (PV) on the 320-K isentropic surface is used to diagnose Rossby waves. The Rossby-wave forecast error in the operational ECMWF high-resolution forecast is shown to be associated with errors in the forecast of a warm conveyor belt (WCB) through trajectory analysis and an error metric for WCB outflows. The WCB forecast error is characterised by an overestimation of WCB amplitude, a location of the WCB outflow regions that is too far to the southeast, and a resulting underestimation of the magnitude of the negative PV anomaly in the outflow. Essentially the same forecast error development also occurred in all members of the ECMWF Ensemble Prediction System and the Met Office MOGREPS-15 suggesting that in this case model error made an important contribution to the development of forecast error in addition to initial condition error. Exploiting this forecast error robustness, a comparison was performed between the realised flow evolution, proxied by a sequence of short-range simulations, and a contemporaneous forecast. Both the proxy to the realised flow and the contemporaneous forecast a were produced with the Met Office Unified Model enhanced with tracers of diabatic processes modifying potential temperature and PV. Clear differences were found in the way potential temperature and PV are modified in the WCB between proxy and forecast. These results demonstrate that differences in potential temperature and PV modification in the WCB can be responsible for forecast errors in Rossby waves

Advances in compilation for quantum hardware -- A demonstration of magic state distillation and repeat-until-success protocols

Fault-tolerant protocols enable large and precise quantum algorithms. Many such protocols rely on a feed-forward processing of data, enabled by a hybrid of quantum and classical logic. Representing the control structure of such programs can be a challenge. Here we explore two such fault-tolerant subroutines and analyze the performance of the subroutines using Quantum Intermediate Representation (QIR) as their underlying intermediate representation. First, we look at QIR's ability to leverage the LLVM compiler toolchain to unroll the quantum iteration logic required to perform magic state distillation on the $[[5,1,3]]$ quantum error-correcting code as originally introduced by Bravyi and Kitaev [Phys. Rev. A 71, 022316 (2005)]. This allows us to not only realize the first implementation of a real-time magic state distillation protocol on quantum hardware, but also demonstrate QIR's ability to optimize complex program structures without degrading machine performance. Next, we investigate a different fault-tolerant protocol that was first introduced by Paetznick and Svore [arXiv:1311.1074 (2013)], that reduces the amount of non-Clifford gates needed for a particular algorithm. We look at four different implementations of this two-stage repeat-until-success algorithm to analyze the performance changes as the results of programming choices. We find the QIR offers a viable representation for a compiled high-level program that performs nearly as well as a hand-optimized version written directly in quantum assembly. Both of these results demonstrate QIR's ability to accurately and efficiently expand the complexity of fault-tolerant protocols that can be realized today on quantum hardware

Differences in microphysical properties of cirrus at high and mid-latitudes

Despite their proven importance for the atmospheric radiative energy budget, the effect of cirrus on climate and the magnitude of their modification by human activity is not well quantified. Besides anthropogenic pollution sources on the ground, aviation has a large local effect on cirrus microphysical and radiative properties via the formation of contrails and their transition to contrail cirrus. To investigate the anthropogenic influence on natural cirrus, we compare the microphysical properties of cirrus measured at mid-latitude (ML) regions (&lt;60∘ N) that are often affected by aviation and pollution with cirrus measured in the same season in comparatively pristine high latitudes (HLs; ≥60∘ N). The number concentration, effective diameter, and ice water content of the observed cirrus are derived from in situ measurements covering ice crystal sizes between 2 and 6400 µm collected during the CIRRUS-HL campaign (Cirrus in High Latitudes) in June and July 2021. We analyse the dependence of cirrus microphysical properties on altitude and latitude and demonstrate that the median ice number concentration is an order of magnitude larger in the measured mid-latitude cirrus, with 0.0086 cm−3, compared to the high-latitude cirrus, with 0.001 cm−3. Ice crystals in mid-latitude cirrus are on average smaller than in high-latitude cirrus, with a median effective diameter of 165 µm compared to 210 µm, and the median ice water content in mid-latitude cirrus is higher (0.0033 g m−3) than in high-latitude cirrus (0.0019 g m−3). In order to investigate the cirrus properties in relation to the region of formation, we combine the airborne observations with 10 d backward trajectories to identify the location of cirrus formation and the cirrus type, i.e. in situ or liquid origin cirrus, depending on whether there is only ice or also liquid water present in the cirrus history, respectively. The cirrus formed and measured at mid-latitudes (M–M) have a particularly high ice number concentration and low effective diameter. This is very likely a signature of contrails and contrail cirrus, which is often observed in the in situ origin cirrus type. In contrast, the largest effective diameter and lowest number concentration were found in the cirrus formed and measured at high latitudes (H–H) along with the highest relative humidity over ice (RHi). On average, in-cloud RHi was above saturation in all cirrus. While most of the H–H cirrus were of an in situ origin, the cirrus formed at mid-latitudes and measured at high latitudes (M–H) were mainly of liquid origin. A pristine Arctic background atmosphere with relatively low ice nuclei availability and the extended growth of few nucleated ice crystals may explain the observed RHi and size distributions. The M–H cirrus are a mixture of the properties of M–M and H–H cirrus (preserving some of the initial properties acquired at mid-latitudes and transforming under Arctic atmospheric conditions). Our analyses indicate that part of the cirrus found at high latitudes is actually formed at mid-latitudes and therefore affected by mid-latitude air masses, which have a greater anthropogenic influence.</p

CHAMP+ observations of warm gas in M17 SW

Since the main cooling lines of the gas phase are important tracers of the interstellar medium in Galactic and extragalactic sources, proper and detailed understanding of their emission, and the ambient conditions of the emitting gas, is necessary for a robust interpretation of the observations. With high resolution (7"-9") maps (~3x3 pc^2) of mid-J molecular lines we aim to probe the physical conditions and spatial distribution of the warm (50 to few hundred K) and dense gas (n(H_2)>10^5 cm^-3) across the interface region of M17 SW nebula. We have used the dual color multiple pixel receiver CHAMP+ on APEX telescope to obtain a 5'.3x4'.7 map of the J=6-5 and J=7-6 transitions of 12CO, the 13CO J=6-5 line, and the {^3P_2}-{^3P_1} 370 um fine-structure transition of [C I] in M17 SW. LTE and non-LTE radiative transfer models are used to constrain the ambient conditions. The warm gas extends up to a distance of ~2.2 pc from the M17 SW ridge. The 13CO J=6-5 and [C I] 370 um lines have a narrower spatial extent of about 1.3 pc along a strip line at P.A=63 deg. The structure and distribution of the [C I] {^3P_2}-{^3P_1} 370 um map indicate that its emission arises from the interclump medium with densities of the order of 10^3 cm^-3. The warmest gas is located along the ridge of the cloud, close to the ionization front. An LTE approximation indicates that the excitation temperature of the embedded clumps goes up to ~120 K. The non-LTE model suggests that the kinetic temperature at four selected positions cannot exceed 230 K in clumps of density n(H_2)~5x10^5 cm^-3, and that the warm T_k>100 K and dense (n(H_2)>10^4 cm^-3) gas traced by the mid-J 12CO lines represent just about 2% of the bulk of the molecular gas. The clump volume filling factor ranges between 0.04 and 0.11 at these positions.Comment: Accepted for publication in Astronomy and Astrophysics, 12 pages, 10 figures, 1 tabl

Formation and evolution of S0 galaxies: a SAURON case study of NGC7332

We present SAURON integral-field observations of the S0 galaxy NGC7332. Existing broad-band ground-based and HST photometry reveals a double disk structure and a boxy bulge interpreted as a bar viewed close to edge-on. The SAURON two-dimensional stellar kinematic maps confirm the existence of the bar and inner disk but also uncover the presence of a cold counter-rotating stellar component within the central 250 pc. The Hbeta and [OIII] emission line maps show that the ionised gas has a complex morphology and kinematics, including both a component counter-rotating with respect to the stars and a fainter co-rotating one. Analysis of the absorption line-strength maps show that NGC7332 is young everywhere. The presence of a large-scale bar can explain most of those properties, but the fact that we see a significant amount of unsettled gas, together with a few peculiar features in the maps, suggest that NGC7332 is still evolving. Interactions as well as bar-driven processes must thus have played an important role in the formation and evolution of NGC7332, and presumably of S0 galaxies in general.Comment: 12 pages, 12 figures, accepted for publication in MNRA