An analysis of interdecadal variations in the perturbational feedback parameter based on a MIROC6 piControl simulation

The climate feedback parameter is a useful indicator for estimating climate sensitivity relating to anthropogenic forcing. This study defines a new feedback parameter, the Perturbational Feedback Parameter (PFP), and the impacts of internally-generated climate variations are clarified using the MIROC piControl simulation. PFP values are found to vary significantly on interdecadal timescales. The equatorial sea surface temperature (SST) has a positive anomaly in the eastern Pacific and a negative anomaly in the western Pacific, and the thermocline tilts more gently than usual when the PFP is large. The statistical properties of the interannual fluctuations also simultaneously vary, and they correspond to the background state. For example, there is an increase in the El Niño Southern Oscillation (ENSO) amplitude relative to the global mean surface temperature rise, and the equatorial high SST more effectively contributes to the southward shift of the Intertropical Convergence Zone (ITCZ). In addition, a decadal fluctuation that dominates over the extratropical northern Pacific also plays an important role in PFP variations. These fluctuations on broad timescales cooperatively induce increases in lower clouds within the subtropics by strengthening the descending flow and static stability, and the consequential net downward radiation flux change through increases in reflection enhances the PFP. In summary, internal changes in both tropical and extratropical variability corresponding to the background state control the strength of the climate feedback on interdecadal timescales.

Towards All-sky Assimilation of Microwave Temperature Sounding Channels in Environment Canada’s Global Deterministic Weather Prediction System

The all-sky assimilation of radiances from microwave instruments is developed in the 4D-EnVar analysis system at Environment and Climate Change Canada (ECCC). Assimilation of cloud-affected radiances from Advanced Microwave Sounding Unit A (AMSUA) temperature sounding channels 4 and 5 for non-precipitating scenes over the ocean surface is the focus of this study. Cloud-affected radiances are discarded in the ECCC operational data assimilation system due to the limitations of forecast model physics, radiative transfer models, and the strong non-linearity of the observation operator. In addition to using symmetric estimate of innovation standard deviation for quality control, a state-dependent observation error inflation is employed at the analysis stage. The background state clouds are scaled by a factor of 0.5 to compensate for a systematic overestimation by the forecast model, before being used in the observation operator. The changes in the fit of the background state to observations show mixed results. The number of AMSUA channels 4 and 5 assimilated observations in the all-sky experiment is 5-12% higher than in the operational system. The all-sky approach improves temperature analysis when verified against ECMWF operational analysis in the areas where the extra cloud-affected observations were assimilated. Statistically significant reductions in error standard deviation by 1-4% for the analysis and forecasts of temperature, specific humidity, and horizontal wind speed up to maximum 4 days were achieved in the all-sky experiment in the lower troposphere. These improvements result mainly from the use of cloud information for computing the observation-minus-background departures. The operational implementation of all-sky assimilation is planned for Fall 2021.

Quarantine and isolation facility: A State Health Department’s response to the COVID-19 pandemic

Background: State Health Departments are at the helm of addressing the myriad needs during the COVID-19 pandemic, including those of vulnerable populations who do not have a place to self-isolate or quarantine to prevent the spread. An estimated 5,000 Arkansas residents face homelessness and are at increased risk of contracting and spreading COVID-19. Additionally, those living in multigenerational families face similar challenges.Objective: We share our experiences and lessons learned in planning, executing, and maintaining a quarantine and isolation facility for vulnerable population during the COVID-19 pandemic.Setting and patients: A 29-bed quarantine and isolation facility was instituted and maintained by the Arkansas Department of Health to meet the quarantine and isolation needs of vulnerable populations. Outcomes and conclusions: As the COVID-19 pandemic persists, need for a facility to meet quarantine and isolation requirements of vulnerable population is not just a critical mitigation strategy but is an ethical imperative.

Mechanism for Southward Shift of Zonal Wind Anomalies During the Mature Phase of ENSO

The cause of southward shift of anomalous zonal wind in the central equatorial Pacific (CEP) during ENSO mature winter was investigated through observational analyses and numerical model experiments. Based on an antisymmetric zonal momentum budget diagnosis using daily ERA-Interim data, a two-step physical mechanism is proposed. The first step involves advection of the zonal wind anomaly by the climatological mean meridional wind. The second step involves the development of an antisymmetric mode in the CEP, which promotes a positive contribution to the observed zonal wind tendency by the pressure gradient and Coriolis forces. Two positive feedbacks are responsible for the growth of the antisymmetric mode. The first involves the moisture–convection–circulation feedback, and the second involves the wind–evaporation–SST feedback. General circulation model experiments further demonstrated that the boreal winter background state is critical in generating the southward shift, and a northward shift of the zonal wind anomaly is found when the same SST anomaly is specified in boreal summer background state.

The problem of diagnosing jet waveguidability in the presence of large-amplitude eddies

The waveguidability of an upper tropospheric zonal jet quantifies its propensity to duct Rossby waves in the zonal direction. This property has played a central role in previous attempts to explain large wave amplitudes and the subsequent occurrence of extreme weather. In these studies, waveguidability was diagnosed with the help of ray tracing arguments using the zonal average of the observed flow as the relevant background state. Here, it is argued that this method is problematic both conceptually and mathematically. The issue is investigated in the framework of the non-divergent barotropic model. This model allows the straightforward computation of an alternative “zonalized” background state, which is obtained through conservative symmetrization of potential vorticity contours and which is argued to be superior to the zonal average. Using an idealized prototypical flow configuration with large-amplitude eddies, it is shown that the two different choices for the background state yield very different results; in particular, the zonal-mean background state diagnoses a zonal waveguide, while the zonalized background state does not. This result suggests that the existence of a waveguide in the zonal mean background state is a consequence of, rather than a precondition for large wave amplitudes, and it would mean that the direction of causality is opposite to the usual argument. The analysis is applied to two heatwave episodes from summer 2003 and 2010, yielding essentially the same result. It is concluded that previous arguments about the role of waveguidability for extreme weather need to be carefully re-evaluated to prevent misinterpretation in the future.

Ensemble Riemannian Data Assimilation over the Wasserstein Space

In this paper, we present an ensemble data assimilation paradigm over a Riemannian manifold equipped with the Wasserstein metric. Unlike the Eulerian penalization of error in the Euclidean space, the Wasserstein metric can capture translation and difference between the shapes of square-integrable probability distributions of the background state and observations – enabling to formally penalize geophysical biases in state-space with non-Gaussian distributions. The new approach is applied to dissipative and chaotic evolutionary dynamics and its potential advantages and limitations are highlighted compared to the classic variational and filtering data assimilation approaches under systematic and random errors.

Diagnosing jet waveguidability in the presence of large-amplitude eddies

<p>The waveguidability of an upper tropospheric zonal jet quantifies its propensity to duct Rossby waves in the zonal direction. This property has played a central role in previous attempts to explain large wave amplitudes and the subsequent occurrence of extreme weather. In these studies, waveguidability was diagnosed with the help of the refractive index using the zonal average of the observed flow as the relevant background state. Here, it is argued that this method is problematic both conceptually and mathematically.</p><p>The issue is investigated in the framework of the non-divergent barotropic model. This model allows the straightforward computation of an alternative "zonalized" background state, which is obtained through conservative symmetrisation of potential vorticity contours and which is argued to be superior to the zonal average. Using an idealized prototypical flow configuration with large-amplitude eddies, it is shown that the two different choices for the background state yield very different results; in particular, the zonal-mean background state diagnoses a zonal waveguide, while the zonalized background state does not. This result suggests that the existence of a waveguide in the zonal mean background state is a consequence of, rather than a precondition for large wave amplitudes, and it would mean that the direction of causality is opposite to the usual argument.</p><p>The analysis is applied to two heatwave episodes from summer 2003 and 2010, yielding essentially the same result. It is concluded that previous arguments about the role of waveguidability for extreme weather need to be carefully re-evaluated to prevent misinterpretation in the future.</p>

Transient Climate Simulations of Orbital Effects on Mesozoic Climates

<p>The Mesozoic era (~252—66 Ma) is traditionally considered as a prolonged greenhouse period, witnessing the breakup of the Pangaean supercontinent. Orbital cycles have, for example, been invoked as drivers of e.g. Pangaean „Megamonsoon“ variability and eustatic sea level cycles in the Mesozoic.</p><p>We aim to contribute to a more comprehensive understanding of orbital effects on Mesozoic climates by employing the newly developed CLIMBER-X Earth System Model. Here, we primarily use its coupled atmosphere, ocean, sea ice and vegetation modules, but also include preliminary tests with dynamic carbon cycle and ice-sheets. We present first results from a set of transient climate simulations of four Mesozoic timeslices representative for Triassic, Jurassic, Early Cretaceous and Late Cretaceous boundary conditions (e.g. paleogeography and solar luminosity). The simulations each cover ~100,000 years and are driven by changing precession, obliquity, and eccentricity.</p><p>We would like to use the opportunity to discuss this approach and associated questions with the community. For example: Would changing paleogeography and climate background state have modified the response to orbital forcings? Could eustatic sea level cycles have been caused by orbitally-driven redistribution of water between the ocean and land water storages or should orbitally-forced ice sheets also have played a role in the alleged Mesozoic greenhouse? Which connections can be established to proxy records?</p>