The ERA5 global reanalysis

Changes in Atmospheric Constituents and in Radiative Forcing

Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

https://dspace.stir.ac.uk/bitstream/1893/30981/1/intcal20_northern_hemisphere_radiocarbon_age_calibration_curve_055_cal_kbp.pdf

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)

This chapter assesses long-term projections of climate change for the end of the 21st century and beyond, where the forced signal depends on the scenario and is typically larger than the internal variability of the climate system. Changes are expressed with respect to a baseline period of 1986-2005, unless otherwise stated.

Chapter 12 - Long-term climate change: Projections, commitments and irreversibility

Hydrogen technologies have experienced cycles of excessive expectations followed by disillusion. Nonetheless, a growing body of evidence suggests these technologies form an attractive option for the deep decarbonisation of global energy systems, and that recent improvements in their cost and performance point towards economic viability as well. This paper is a comprehensive review of the potential role that hydrogen could play in the provision of electricity, heat, industry, transport and energy storage in a low-carbon energy system, and an assessment of the status of hydrogen in being able to fulfil that potential. The picture that emerges is one of qualified promise: hydrogen is well established in certain niches such as forklift trucks, while mainstream applications are now forthcoming. Hydrogen vehicles are available commercially in several countries, and 225 000 fuel cell home heating systems have been sold. This represents a step change from the situation of only five years ago. This review shows that challenges around cost and performance remain, and considerable improvements are still required for hydrogen to become truly competitive. But such competitiveness in the medium-term future no longer seems an unrealistic prospect, which fully justifies the growing interest and policy support for these technologies around the world.

https://pubs.rsc.org/en/content/articlepdf/2019/ee/c8ee01157e

The role of hydrogen and fuel cells in the global energy system


In recent decades the Arctic has warmed faster than the global mean, especially during winter. This has been attributed to various causes, with recent studies highlighting the importance of enhanced downward infrared radiation associated with anomalous inflow of warm, moist air from lower latitudes. Here we study wintertime surface energy budget (SEB) anomalies over Arctic sea-ice on synoptic time scales, using ERA5 reanalyses (1979–2020). We introduce a new algorithm to identify areas with extreme positive daily-mean SEB anomalies and connect them to form spatio-temporal life-cycle events. Most of these events are associated with large-scale inflow from the Atlantic/Pacific Oceans, driven by poleward deflection of the storm track and blocks over northern Eurasia/Alaska. Events originate near the ice edge, where they have roughly equal contributions of net longwave radiation and turbulent fluxes to the positive SEB anomaly. As the events move further into the Arctic, SEB anomalies decrease due to weakening sensible and latent heat flux anomalies, while the surface temperature anomaly increases towards the peak of the events along with the downward longwave radiation anomaly. Due to these temporal and spatial differences, the largest SEB anomalies are not always related to strongest surface warming. Thus, studying temperature anomalies alone might not be sufficient to determine sea-ice changes. This study highlights the importance of turbulent fluxes in driving SEB anomalies and downward longwave radiation in determining local surface warming. Therefore, both processes need to be accurately represented in climate models.

/pdf/extreme-surface-energy-budget-anomalies-in-the-high-arctic-2dq1no1l.pdf

Extreme Surface Energy Budget Anomalies in the High Arctic in Winter

Abstract. During a research flight of the Wave-driven ISentropic
Exchange (WISE) campaign, which was conducted over the eastern North
Atlantic on 1 October 2017, the composition of the upper troposphere and
lower stratosphere (UTLS) across the North Atlantic jet stream was observed
by airborne, range-resolved differential absorption lidar (DIAL) profiles.
We investigate how the high variability in the paired H2O and O3 distribution along the two-dimensional lidar cross section is affected by
synoptic-scale weather systems, as revealed by the Lagrangian history of the
observed air masses. To this aim, the lidar observations are combined with
10 d backward trajectories along which meteorological parameters and
derived turbulence diagnostics are traced. The transport and mixing
characteristics are then projected to the vertical cross sections of the
lidar measurements and to the H2O–O3 phase space to explore
linkages with the evolution of synoptic-scale weather systems and their
interaction. Tropical, midlatitude, and arctic weather systems in the region
of the jet stream and the related transport and mixing explain the complex
H2O and O3 distribution to a large extent: O3-rich
stratospheric air from the high Arctic interacts with midlatitude air from
the North Pacific in a northward-deflected jet stream associated with an
anticyclone over the US and forms a filament extending into the tropopause
fold beneath the jet stream. In the troposphere, lifting related to
convection in the intertropical convergence zone (ITCZ) and two tropical
cyclones that continuously injected H2O into dry descending air from
the tropical Atlantic and Pacific form filamentary H2O structures. One
tropical cyclone that transitioned into a midlatitude cyclone lifted moist
boundary layer air, explaining the highest tropospheric H2O values.
During the two days before the observations, the air with mixed tropospheric
and stratospheric characteristics experienced frequent turbulence along the
North Atlantic jet stream, indicating a strong influence of turbulence on the
formation of the extratropical transition layer (ExTL). This investigation
highlights the complexity of stirring and mixing processes and their close
connection to interacting tropospheric weather systems from the tropics to the
polar regions, which strongly influenced the observed fine-scale H2O
and O3 distributions. The identified non-local character of
mixing should be kept in mind when interpreting mixing lines in
tracer–tracer phase space diagrams.


Case study on the influence of synoptic-scale processes on the paired H2O–O3 distribution in the UTLS across a North Atlantic jet stream


Meteorological extremes on the seasonal time scale have received increased attention due to their relevance for society and economy. A recently developed approach to identify seasonal extremes is applied here to ERA5 reanalyses from 1950-2020 to identify hot and cold, wet and dry, and stormy and calm extreme seasons globally. The approach consists of (i) fitting a statistical model to seasonal mean values (of temperature, precipitation, and wind speed) at each grid point, (ii) selecting a local return period threshold above which seasonal mean values are deemed extreme, and (iii) forming spatially coherent extreme season objects. The paper introduces the ERA5 extreme season explorer, an open-accessweb-portal enabling researchers to visualise and download extreme season objects of any of the six types in their region of interest, for further investigating their underlying dynamics, statistical properties, and impacts. To illustrate the potential of our extreme season objects, we first discuss the top 10 cold winters in ERA5 globally and then focus on an unusual triple-compound extreme season in winter 1953/54 in Europe, which was simultaneously extremely cold, dry, and calm. We show that detailed analysis of weather system dynamics, including cyclones, blocks, jets, and Rossby waves, provides important insight into the processes leading to extreme seasons. In summary, this study presents for the first time a catalogue of objectively identified extreme seasons in the last decades, shows exemplarily how large-scale dynamics can lead to such seasons, and with the help of the explorer supports the community in accelerating research in this important area at the interface of weather and climate dynamics.

The ERA5 extreme seasons explorer as a basis for research at the weather and climate interface

The Relationship between Warm Conveyor Belts, Tropical Moisture Exports and Atmospheric Rivers

Abstract. During a research flight of the Wave-driven ISentropic Exchange (WISE) campaign, which was conducted over the eastern North Atlantic on 1 October 2017, the composition of the Upper Troposphere and Lower Stratosphere (UTLS) across the North Atlantic jet stream was observed by airborne, range-resolved Differential Absorption Lidar (DIAL) profiles. We investigate how the high variability in the paired H2O and O3 distribution along the two-dimensional lidar cross section is affected by synoptic-scale weather systems, as revealed by the Lagrangian history of the observed air masses. To this aim, the lidar observations are combined with 10-day backward trajectories along which meteorological parameters and derived turbulence diagnostics are traced. The transport and mixing characteristics are then projected to the vertical cross sections of the lidar measurements and to the H2O–O3 phase space to explore linkages with the evolution of synoptic scale weather systems and their interaction. Tropical, midlatitude and arctic weather systems in the region of the jet stream and the related transport and mixing explain the complex H2O and O3 distribution to a large extent: O3-rich stratospheric air from the high Arctic interacts with midlatitude air from the North Pacific in a northward deflected jet stream associated with an anticyclone over the US and forms a filament extending into the tropopause fold beneath the jet stream. In the troposphere, lifting related to convection in the innertropical convergence zone (ITCZ) and two tropical cyclones continuously injected H2O into dry descending air from the tropical Atlantic and Pacific forming filamentary H2O structures. One tropical cyclone that transitioned into a midlatitude cyclone lifted moist boundary layer air explaining the highest tropospheric H2O values. During the two days before the observations the air with mixed tropospheric and stratospheric characteristics experienced frequent turbulence along the North Atlantic jet stream indicating a strong influence of turbulence on the formation of the Extratropical Transition Layer (ExTL). This investigation highlights the complexity of stirring and mixing processes and their close connection to interacting tropospheric weather systems from the tropics to polar regions, which strongly influenced the observed fine-scale H2O and O3 distributions. The identified non-local character of mixing should be kept in mind when interpreting mixing lines in tracer–tracer phase space diagrams. 

/pdf/case-study-on-the-influence-of-synoptic-scale-processes-on-1outxjze.pdf

Case study on the influence of synoptic-scale processes on the paired H<sub>2</sub>O-O<sub>3</sub> distribution in the UTLS across a North Atlantic jet stream

Heini Wernli

Papers

Extreme Surface Energy Budget Anomalies in the High Arctic in Winter

Case study on the influence of synoptic-scale processes on the paired H2O–O3 distribution in the UTLS across a North Atlantic jet stream

The ERA5 extreme seasons explorer as a basis for research at the weather and climate interface

The Relationship between Warm Conveyor Belts, Tropical Moisture Exports and Atmospheric Rivers

Case study on the influence of synoptic-scale processes on the paired H<sub>2</sub>O-O<sub>3</sub> distribution in the UTLS across a North Atlantic jet stream