The climate research community uses atmospheric reanalysis data sets to understand a wide range of processes and variability in the atmosphere, yet different reanalyses may give very different results for the same diagnostics. The Stratosphere–troposphere Processes And their Role in Climate (SPARC) Reanalysis Intercomparison Project (S-RIP) is a coordinated activity to compare reanalysis data sets using a variety of key diagnostics. The objectives of this project are to identify differences among reanalyses and understand their underlying causes, to provide guidance on appropriate usage of various reanalysis products in scientific studies, particularly those of relevance to SPARC, and to contribute to future improvements in the reanalysis products by establishing collaborative links between reanalysis centres and data users. The project focuses predominantly on differences among reanalyses, although studies that include operational analyses and studies comparing reanalyses with observations are also included when appropriate. The emphasis is on diagnostics of the upper troposphere, stratosphere, and lower mesosphere. This paper summarizes the motivation and goals of the S-RIP activity and extensively reviews key technical aspects of the reanalysis data sets that are the focus of this activity. The special issue \"The SPARC Reanalysis Intercomparison Project (S-RIP)\" in this journal serves to collect research with relevance to the S-RIP in preparation for the publication of the planned two (interim and full) S-RIP reports.

Introduction to the SPARC Reanalysis Intercomparison Project (S-RIP)

The climatology of (severe) thunderstorm days is investigated on a pan-European scale for the period of 1979–2017. For this purpose, sounding measurements, surface observations, lightning d...

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A Climatology of Thunderstorms across Europe from a Synthesis of Multiple Data Sources

In this study we investigate convective environments and their corresponding climatological features over Europe and the United States. For this purpose, National Lightning Detection Network (NLDN) and Arrival Time Difference long-range lightning detection network (ATDnet) data, ERA5 hybrid-sigma levels, and severe weather reports from the European Severe Weather Database (ESWD) and Storm Prediction Center (SPC) Storm Data were combined on a common grid of 0.25° and 1-h steps over the period 1979–2018. The severity of convective hazards increases with increasing instability and wind shear (WMAXSHEAR), but climatological aspects of these features differ over both domains. Environments over the United States are characterized by higher moisture, CAPE, CIN, wind shear, and midtropospheric lapse rates. Conversely, 0–3-km CAPE and low-level lapse rates are higher over Europe. From the climatological perspective severe thunderstorm environments (hours) are around 3–4 times more frequent over the United States with peaks across the Great Plains, Midwest, and Southeast. Over Europe severe environments are the most common over the south with local maxima in northern Italy. Despite having lower CAPE (tail distribution of 3000–4000 J kg−1 compared to 6000–8000 J kg−1 over the United States), thunderstorms over Europe have a higher probability for convective initiation given a favorable environment. Conversely, the lowest probability for initiation is observed over the Great Plains, but, once a thunderstorm develops, the probability that it will become severe is much higher compared to Europe. Prime conditions for severe thunderstorms over the United States are between April and June, typically from 1200 to 2200 central standard time (CST), while across Europe favorable environments are observed from June to August, usually between 1400 and 2100 UTC.

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Severe Convective Storms across Europe and the United States. Part II: ERA5 Environments Associated with Lightning, Large Hail, Severe Wind, and Tornadoes

We compare over 1 million sounding measurements with ERA-Interim reanalysis for the 38-yr period from 1979 to 2016. The large dataset allows us to provide an improved insight into the spati...

Climatological Aspects of Convective Parameters over Europe: A Comparison of ERA-Interim and Sounding Data

The performance of a new historical reanalysis, the NOAA–CIRES–DOE Twentieth Century Reanalysis version 3 (20CRv3), is evaluated via comparisons with other reanalyses and independent observations. This dataset provides global, 3-hourly estimates of the atmosphere from 1806 to 2015 by assimilating only surface pressure observations and prescribing sea surface temperature, sea ice concentration, and radiative forcings. Comparisons with independent observations, other reanalyses, and satellite products suggest that 20CRv3 can reliably produce atmospheric estimates on scales ranging from weather events to long-term climatic trends. Not only does 20CRv3 recreate a “best estimate” of the weather, including extreme events, it also provides an estimate of its confidence through the use of an ensemble. Surface pressure statistics suggest that these confidence estimates are reliable. Comparisons with independent upper-air observations in the Northern Hemisphere demonstrate that 20CRv3 has skill throughout the twentieth century. Upper-air fields from 20CRv3 in the late twentieth century and early twenty-first century correlate well with full-input reanalyses, and the correlation is predicted by the confidence fields from 20CRv3. The skill of analyzed 500-hPa geopotential heights from 20CRv3 for 1979–2015 is comparable to that of modern operational 3–4-day forecasts. Finally, 20CRv3 performs well on climate time scales. Long time series and multidecadal averages of mass, circulation, and precipitation fields agree well with modern reanalyses and station- and satellite-based products. 20CRv3 is also able to capture trends in tropospheric-layer temperatures that correlate well with independent products in the twentieth century, placing recent trends in a longer historical context.

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An Evaluation of the Performance of the Twentieth Century Reanalysis Version 3

Tropospheric temperature inversions seem to be an important feature of climate, as well as a significant factor affecting air quality and fog formation. The aim of this article is to investigate the temporal and spatial variability of surface-based inversions (SBIs) over Europe. It is based on data derived from the ERA-Interim reanalysis for the period 1981–2015. The study examines diurnal, seasonal and multiannual variability of temperature inversions based on their frequency, depth and strength. These three parameters are characterized by strong temporal variability – diurnal and seasonal, as well as strong spatial differentiation. It has been confirmed that the energy budget is the key factor responsible for diurnal, and partly seasonal variability of SBI occurrence. Its negative values lead to an intense cooling of active surface and initiate the formation of the radiative inversions, which are the most common type of inversion occurring over the mainland of Europe. Temperature inversions usually form shortly after dusk, increasing gradually their depth and strength until sunrise. At 0000 Universal Time Coordinated (UTC), SBI frequency attains higher values in the summer than in the winter over the predominant part of Europe. However, the inversion layers occurring then are noticeably shallower and weaker. Surface type strongly affects SBI properties. This is mostly marked in terms of the distinct differentiation between marine and land areas as well as the impact of vast glaciers located across Greenland and western part of Iceland. Moreover, the distribution of SBI depth and strength is shaped by atmospheric circulation. For instance, their higher values occur over Eastern Europe in the winter, which is associated with the influence of a seasonal high pressure system found over Russia. Taking into account multiannual variability, SBI parameters, primarily depth and strength, exhibit the most significant negative changes in the winter.

Temporal and spatial variability of surface‐based inversions over Europe based on ERA‐Interim reanalysis

The occurrence of convective systems with a bow echo in warm season in Poland

⎯ Heavy rainfalls and consequent floods are the most important extreme events in Central Europe in terms of frequency and economic losses. The purpose of the study is to evaluate regional extreme precipitation events in the Polish Carpathian Mountains as well as to determine the circulation basis for these events. Extreme precipitation values were identified based on daily precipitation totals measured at almost 70 weather stations in the Polish Carpathians between 1951 and 2015. The analysis concentrates on daily mean areal precipitation totals in excess of 100 mm per day as well as 50 and 30 mm, which causes flooding in the Carpathians. All extreme precipitation data were analyzed from a synoptic perspective, with special attention paid to pressure patterns over Central Europe. The analysis confirms that the heaviest rainfalls are affected by the situations with the NNE airflow. However, analyses with the application of the upper tropospheric data brought some new findings on the precipitation extreme topic. It turned out that most cases with significant rains occurred when the mid-tropospheric advection was from the southern sector (during the typical N and NE advections in the lower part). Key–words: precipitation totals, extremes, atmospheric circulation, Carpathians

Extreme precipitation events in the Polish Carpathians and their synoptic determinants

Severe wind events are often related to the occurrence of mesoscale convective systems with arch-shaped radar reflectivity, i.e., a bow echo. In this research, the kinematic and thermodynamic conditions associated with 91 bow echo cases which occurred in the warm season (i.e., from early April until late September) in Poland (2007–2014) were analyzed. The environmental conditions were determined primarily based on the upper air soundings, and additionally on data obtained from ERA-Interim reanalysis. The results indicate that there is a relatively wide range of shear and instability environments associated with bow echoes over Poland. The identified cases occurred both in weakly forced environments, and as well developed in dynamic synoptic patterns with low instability. We have also found cases with strong instability and significantly increased shear values. The combination of a moist boundary layer and steep mid-tropospheric lapse rate usually resulted in moderate to high CAPE values for identified bow echo cases. The median of surface-based CAPE was equal to 1594 J/kg (Mean Layer CAPE = 1038 J/kg) for soundings, and to 1622 J/kg (Mean Layer CAPE = 1275 J/kg) for ERA-Interim. Bow echo environments also showed significantly increased potential for strong downdrafts and damaging outflow winds (the median Downdraft CAPE reached 849 J/kg for soundings and 734 J/kg for ERA-Interim). Bow echoes were usually associated with the occurrence of strong air flow in the troposphere. The presence of a jet stream in the middle and upper troposphere contributed to the development of increased vertical wind shear values. The median of 0–6-km shear exceeded 15 m/s, whereas for 0–3-km shear, it was approximately equal to 12.5 m/s and to 7 m/s for 0–1-km shear.

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Kinematic and thermodynamic conditions related to convective systems with a bow echo in Poland

Although tropospheric temperature inversions are thought to be an important feature of climate as well as a significant factor affecting air quality, low-level cloud formation, and the radiation budget of the Earth, a quantitative assessment of their representation in atmospheric reanalyses is still missing from the scientific literature. Here, we provide new evidence of the occurrence of low-tropospheric temperature inversions and associated uncertainties in their parameters existing among reanalyses produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) and upper-air soundings for Europe covering the period 2001-2010. The reanalyses utilized here may be grouped into two categories: (1) surface-input reanalyses represented by ERA-20C and CERA-20C as well as (2) full-input reanalyses represented by ERA-Interim and ERA5. The upper-air soundings were derived from the Integrated Global Radiosonde Archive (IGRA), version 2. The data consist mainly of air temperature and geopotential height from the model levels (ModLev) and pressure levels (PresLev)of ECMWF reanalyses. The results have demonstrated that the frequency of surface-based inversions (SBI) and elevated inversions (EI) is largely in agreement among the reanalyses. The quality of their representation is, however, determined by the inversion type, season, and region. Over the vast majority of IGRA upper-air stations, SBI frequency is overestimated and EI frequency is underestimated by ECMWF reanalyses. Substantially larger uncertainties arise from the selection between the data of ModLev and PresLev of the reanalyses– the differences in the frequency of the temperature inversions calculated based on those data are particularly large for summertime SBI suggesting that PresLev are not capable of resolving the main features of shallow and weak SBI.

https://iopscience.iop.org/article/10.1088/1748-9326/ab7d5d/pdf

Angelika Palarz

Papers

Temporal and spatial variability of surface‐based inversions over Europe based on ERA‐Interim reanalysis

The occurrence of convective systems with a bow echo in warm season in Poland

Extreme precipitation events in the Polish Carpathians and their synoptic determinants

Kinematic and thermodynamic conditions related to convective systems with a bow echo in Poland

Representation of low-tropospheric temperature inversions in ECMWF reanalyses over Europe