scholarly journals Inconsistencies between Long-Term Trends in Storminess Derived from the 20CR Reanalysis and Observations

2013 ◽  
Vol 26 (3) ◽  
pp. 868-874 ◽  
Author(s):  
Oliver Krueger ◽  
Frederik Schenk ◽  
Frauke Feser ◽  
Ralf Weisse
Keyword(s):  
Twentieth Century ◽  
Climate Variability ◽  
Climate Models ◽  
Reanalysis Dataset ◽  
Northeast Atlantic ◽  
Long Term Trends ◽  
Storm Index ◽  
Global Reanalysis ◽  
Long Term Trend

Abstract Global atmospheric reanalyses have become a common tool for both validation of climate models and diagnostic studies, such as assessing climate variability and long-term trends. Presently, the Twentieth Century Reanalysis (20CR), which assimilates only surface pressure reports, sea ice, and sea surface temperature distributions, represents the longest global reanalysis dataset available covering the period from 1871 to the present. Currently the 20CR dataset is extensively used for the assessment of climate variability and trends. Here, the authors compare the variability and long-term trends in northeast Atlantic storminess derived from 20CR and from observations. A well-established storm index derived from pressure observations over a relatively densely monitored marine area is used. It is found that both variability and long-term trends derived from 20CR and from observations are inconsistent. In particular, both time series show opposing trends during the first half of the twentieth century: both storm indices share a similar behavior only for the more recent periods. While the variability and long-term trend derived from the observations are supported by a number of independent data and analyses, the behavior shown by 20CR is quite different, indicating substantial inhomogeneities in the reanalysis, most likely caused by the increasing number of observations assimilated into 20CR over time. The latter makes 20CR likely unsuitable for the identification of trends in storminess in the earlier part of the record, at least over the northeast Atlantic. The results imply and reconfirm previous findings that care is needed in general when global reanalyses are used to assess long-term changes.

Northeast Atlantic storminess in centennial reanalyses

2021 ◽  
Author(s):  
Oliver Krueger ◽  
Frauke Feser ◽  
Christopher Kadow ◽  
Ralf Weisse
Keyword(s):  
Climate Models ◽  
Numerical Models ◽  
Geostrophic Wind ◽  
Model Systems ◽  
Storm Activity ◽  
Northeast Atlantic ◽  
Wind Speeds ◽  
Long Term Trends ◽  
Storm Index

<p>Global atmospheric reanalyses are commonly applied for the validation of climate models, diagnostic studies, and driving higher resolution numerical models with the emphasis on assessing climate variability and long-term trends. Over recent years, longer reanalyses spanning a period of more than hundred years have become available. In this study, the variability and long-term trends of storm activity is assessed over the northeast Atlantic in modern centennial reanalysis datasets, namely ERA-20cm, ERA-20c, CERA-20c, and the 20CR-reanalysis suite with 20CRv3 being the most recent one. All reanalyses, except from ERA-20cm, assimilate surface pressure observations, whereby ERA-20C and CERA-20c additionally assimilate surface winds. For the assessment, the well-established storm index of higher annual percentiles of geostrophic wind speeds derived from pressure observations at sea level over a relatively densely monitored marine area is used.</p><p>The results indicate that the examined centennial reanalyses are not able to represent long-term trends of storm activity over the northeast Atlantic, particularly in the earlier years of the period examined when compared with the geostrophic wind index based on pressure observations. Moreover, the reanalyses show inconsistent long-term behaviour when compared with each other. Only in the latter half of the 20th century, the variability of reanalysed and observed storminess time series starts to agree with each other. Additionally, 20CRv3, the most recent centennial reanalysis examined, shows markedly improved results with increased uncertainty, albeit multidecadal storminess variability does not match observed values in earlier times before about 1920.</p><p>The behaviour shown by the centennial reanalyses are likely caused by the increasing number of assimilated observations, changes in the observational databases used, and the different underlying numerical model systems. Furthermore, the results derived from the ERA-20cm reanalysis that does not assimilate any pressure or wind observations suggests that the variability and uncertainty of storminess over the northeast Atlantic is high making it difficult to determine storm activity when numerical models are not bound by observations. The results of this study imply and reconfirm previous findings that the assessment of long-term storminess trends and variability in centennial reanalyses remains a rather delicate matter, at least for the northeast Atlantic region.</p>

Long-term Trend Comparison of Planetary Boundary Layer Height in Observations and CMIP6 models over China

2021 ◽  
Author(s):  
Man Yue ◽  
Minghuai Wang ◽  
Jianping Guo ◽  
Haipeng Zhang ◽  
Xinyi Dong ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Cloud Cover ◽  
Climate Models ◽  
Term Trend ◽  
Cloud Radiative Effect ◽  
Low Cloud ◽  
Long Term Trends ◽  
Low Cloud Cover ◽  
Long Term Trend

<p>The planetary boundary layer (PBL) plays an essential role in climate and air quality simulations. Large uncertainties remain in understanding the long-term trend of PBL height (PBLH) and its simulation. Here we use the radiosonde data and reanalysis datasets to analyze PBLH long-term trends over China, and to further evaluate the performance of CMIP6 climate models in simulating these trends. Results show that the observed long-term “positive to negative” trend shift of PBLH is related to the variation in the surface upward sensible heat flux (SHFLX) which is further controlled by the synergistic effect of low cloud cover (LCC) and soil moisture (SM) changes. Variabilities in low cloud cover and soil moisture directly influence the energy balance via surface net downward shortwave flux (SWF) and the latent heat flux (LHFLX), respectively. We have found that the CMIP6 climate models cannot reproduce the observed PBLH long-term trend shift over China. The CMIP6 results show an overwhelming continuous downward PBLH trend during the 1979-2014 period, which is caused by the poorly simulated long-term changes of cloud radiative effect. Our results reveal that the long-term cloud radiative effect simulation is critical for CMIP6 models in reproducing the PBLH long-term trends. This study highlights the importance of low cloud cover and soil moisture processes in modulating PBLH long-term variations and calls attentions to improve these processes in climate models in order to improve the PLBH long-term trend simulations.</p>

scholarly journals Climate Drift in the CMIP3 Models

2012 ◽  
Vol 25 (13) ◽  
pp. 4621-4640 ◽  
Author(s):  
Alexander Sen Gupta ◽  
Les C. Muir ◽  
Jaclyn N. Brown ◽  
Steven J. Phipps ◽  
Paul J. Durack ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Sea Level ◽  
Climate Models ◽  
Steric Sea Level ◽  
Climate Simulations ◽  
Long Term Trends ◽  
Climate Drift ◽  
Component Models ◽  
Global And Local

Abstract Even in the absence of external forcing, climate models often exhibit long-term trends that cannot be attributed to natural variability. This so-called climate drift arises for various reasons including the following: perturbations to the climate system on coupling component models together and deficiencies in model physics and numerics. When examining trends in historical or future climate simulations, it is important to know the error introduced by drift so that action can be taken where necessary. This study assesses the importance of drift for a number of climate properties at global and local scales. To illustrate this, the present paper focuses on simulated trends over the second half of the twentieth century. While drift in globally averaged surface properties is generally considerably smaller than observed and simulated twentieth-century trends, it can still introduce nontrivial errors in some models. Furthermore, errors become increasingly important at smaller scales. The direction of drift is not systematic across different models or variables, as such drift is considerably reduced in the multimodel mean. Despite drift being primarily associated with ocean adjustment, it is also apparent in atmospheric variables. For example, most models have local drift magnitudes in surface air and ocean temperatures that are typically between 15% and 35% of the twentieth-century simulation trend magnitudes for 1950–2000. Below depths of 1000–2000 m, drift dominates over any forced trend in most regions. As such steric sea level is strongly affected and for some models and regions the sea level trend direction is reversed. Thus depending on the application, drift may be negligible or may make up an important part of the simulated trend.

scholarly journals Different long-term trends of the oxygen red 630.0 nm line nightglow intensity as the result of lowering the ionosphere F2 layer

2008 ◽  
Vol 26 (8) ◽  
pp. 2069-2080 ◽  
Author(s):  
N. B. Gudadze ◽  
G. G. Didebulidze ◽  
L. N. Lomidze ◽  
G. Sh. Javakhishvili ◽  
M. A. Marsagishvili ◽  
...  
Keyword(s):  
Electron Density ◽  
Line Intensity ◽  
Peak Height ◽  
Height Distribution ◽  
Theoretical Simulation ◽  
Type Layer ◽  
Long Term Trends ◽  
The Mean ◽  
Long Term Trend

Abstract. Long-term observations of total nightglow intensity of the atomic oxygen red 630.0 nm line at Abastumani (41.75° N, 42.82° E) in 1957–1993 and measurements of the ionosphere F2 layer parameters from the Tbilisi ionosphere station (41.65° N, 44.75° E) in 1963–1986 have been analyzed. It is shown that a decrease in the long-term trend of the mean annual red 630.0 nm line intensity from the pre-midnight value (+0.770±1.045 R/year) to its minimum negative value (−1.080±0.670 R/year) at the midnight/after midnight is a possible result of the observed lowering of the peak height of the ionosphere F2 layer electron density hmF2 (−0.455±0.343 km/year). A theoretical simulation is carried out using a simple Chapman-type layer (damping in time) for the height distribution of the F2 layer electron density. The estimated values of the lowering in the hmF2, the increase in the red line intensity at pre-midnight and its decrease at midnight/after midnight are close to their observational ones, when a negative trend in the total neutral density of the upper atmosphere and an increase in the mean northward wind (or its possible consequence – a decrease in the southward one) are assumed.

scholarly journals Atmosphere similarity patterns in boreal summer show an increase of persistent weather conditions connected to hydro-climatic risks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Peter Hoffmann ◽  
Jascha Lehmann ◽  
Bijan H. Fallah ◽  
Fred F. Hattermann
Keyword(s):  
Northern Hemisphere ◽  
Climate Models ◽  
Weather Conditions ◽  
Boreal Summer ◽  
Climatic Extremes ◽  
Weather Patterns ◽  
Dry Conditions ◽  
Climatic Risks ◽  
Long Term Trend

AbstractRecent studies have shown that hydro-climatic extremes have increased significantly in number and intensity in the last decades. In the Northern Hemisphere such events were often associated with long lasting persistent weather patterns. In 2018, hot and dry conditions prevailed for several months over Central Europe leading to record-breaking temperatures and severe harvest losses. The underlying circulation processes are still not fully understood and there is a need for improved methodologies to detect and quantify persistent weather conditions. Here, we propose a new method to detect, compare and quantify persistence through atmosphere similarity patterns by applying established image recognition methods to day to day atmospheric fields. We find that persistent weather patterns have increased in number and intensity over the last decades in Northern Hemisphere mid-latitude summer, link this to hydro-climatic risks and evaluate the extreme summers of 2010 (Russian heat wave) and of 2018 (European drought). We further evaluate the ability of climate models to reproduce long-term trend patterns of weather persistence and the result is a notable discrepancy to observed developments.

Alternate history: A synthetic ensemble of ocean chlorophyll concentrations

2021 ◽  
Author(s):  
Geneviève Elsworth ◽  
Nicole Lovenduski ◽  
Karen McKinnon
Keyword(s):  
Climate Variability ◽  
Internal Variability ◽  
Ensemble Member ◽  
Global Ocean ◽  
Large Ensemble ◽  
Internal Climate Variability ◽  
Surface Ocean ◽  
Large Ensembles ◽  
Long Term Trends

<p>Internal climate variability plays an important role in the abundance and distribution of phytoplankton in the global ocean. Previous studies using large ensembles of Earth system models (ESMs) have demonstrated their utility in the study of marine phytoplankton variability. These ESM large ensembles simulate the evolution of multiple alternate realities, each with a different phasing of internal climate variability. However, ESMs may not accurately represent real world variability as recorded via satellite and in situ observations of ocean chlorophyll over the past few decades. Observational records of surface ocean chlorophyll equate to a single ensemble member in the large ensemble framework, and this can cloud the interpretation of long-term trends: are they externally forced, caused by the phasing of internal variability, or both? Here, we use a novel statistical emulation technique to place the observational record of surface ocean chlorophyll into the large ensemble framework. Much like a large initial condition ensemble generated with an ESM, the resulting synthetic ensemble represents multiple possible evolutions of ocean chlorophyll concentration, each with a different phasing of internal climate variability. We further demonstrate the validity of our statistical approach by recreating a ESM ensemble of chlorophyll using only a single ESM ensemble member. We use the synthetic ensemble to explore the interpretation of long-term trends in the presence of internal variability. Our results suggest the potential to explore this approach for other ocean biogeochemical variables.</p>

On fragile democracy: Contemporary and historical perspectives—Introduction

2019 ◽  
Vol 17 (4) ◽  
pp. 422-431
Author(s):  
Martin Conway
Keyword(s):  
Twentieth Century ◽  
Special Issue ◽  
Historical Perspectives ◽  
Alternative Means ◽  
History Of ◽  
Long Term Trends

The concept of fragility provides an alternative means of approaching the history of democracy, which has often been seen as the ineluctable consequence of Europe’s social and political modernisation. This is especially so in Scandinavia, as well as in Finland, where the emergence of a particular Nordic model of democracy from the early decades of the twentieth century onwards has often been explained with reference to embedded traditions of local self-government and long-term trends towards social egalitarianism. In contrast, this article emphasises the tensions present within the practices and understandings of democracy in the principal states of Scandinavia during the twentieth century. In doing so, it provides an introduction to the articles that compose this Special Issue, as well as contributing to the wider literature on the fragility of present-day structures of democracy.

scholarly journals Long-term trends in the relation between daytime and nighttime values of <I>fo</I>F2

2008 ◽  
Vol 26 (5) ◽  
pp. 1199-1206 ◽  
Author(s):  
A. D. Danilov
Keyword(s):  
Solar Activity ◽  
Term Trend ◽  
The World ◽  
Long Term Changes ◽  
Long Term Trends ◽  
Thermospheric Winds ◽  
Long Term Trend ◽  
Ionospheric Sounding ◽  
Limiting Value

Abstract. The data from the vertical ionospheric sounding for 12 stations over the world were analyzed to find the relation between the values of foF2 for 02:00 LT and 14:00 LT of the same day. It is found that, in general, there exists a negative correlation between foF2(02) and foF2(14). The value of the correlation coefficient R(foF2) can be in some cases high enough and reach minus 0.7–0.8. The value of R(foF2) demonstrates a well pronounced seasonal variations, the highest negative values being observed at the equinox periods of the year. It is also found that R(foF2) depends on geomagnetic activity: the magnitude of R(foF2) is the highest for the choice of only magnetically quiet days (Ap<6), decreasing with the increase of the limiting value of Ap. For a fixed limitation on Ap, the value of R(foF2) depends also on solar activity. Apparently, the effects found are related to thermospheric winds. Analysis of long series of the vertical sounding data shows that there is a long-term trend in R(foF2) with a statistically significant increase in the R(foF2) magnitude after about 1980. Similar analysis is performed for the foF2(02)/foF2(14) ratio itself. The ratio also demonstrates a systematic trend after 1980. Both trends are interpreted in terms of long-term changes in thermospheric circulation.

Long-term trend analysis of deep-ocean acoustic noise data

2020 ◽  
Author(s):  
Sei-Him Cheong ◽  
Stephen P Robinson ◽  
Peter M Harris ◽  
Lian S Wang ◽  
Valerie Livina
Keyword(s):  
Trend Analysis ◽  
Sound Pressure ◽  
Functional Model ◽  
Deep Ocean ◽  
Ocean Noise ◽  
Noise Data ◽  
Long Term Trends ◽  
Long Term Trend ◽  
Monitoring Stations

&lt;p&gt;Underwater noise is recognised as a form of marine pollutant and there is evidence that over exposure to excessive levels of noise can have effects on the wellbeing of the marine ecosystem. Consequently, the variation in the ambient sound levels in the deep ocean has been the subject of a number of recent studies, with particular interest in the identification of long-term trends. We describe a statistical method for performing long-term trend analysis and uncertainty evaluation of the estimated trends from deep-ocean noise data. This study has been extended to include &amp;#160;measured data&amp;#160; from four monitoring stations located in the Indian (Cape Leeuwin &amp; Diego Garcia), Pacific (Wake Island) and Southern Atlantic (Ascension Islands) Oceans over periods spanning between 8 to 15 years. The data were obtained from the hydro-acoustic monitoring stations of the Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO). The monitoring stations provide information at a sampling frequency of 250 Hz, leading to very large datasets, and at acoustic frequencies up to 105 Hz.&lt;/p&gt;&lt;p&gt;The analysis method uses a flexible discrete model that incorporates terms that capture seasonal variations in the data together with a moving-average statistical model to describe the serial correlation of residual deviations. The trend analysis is applied to time series representing daily aggregated statistical levels for four frequency bands to obtain estimates for the change in sound pressure level (SPL) over the examined period with associated coverage intervals. The analysis demonstrates that there are statistically significant changes in the levels of deep-ocean noise over periods exceeding a decade. The main features of the approach include (a) using a functional model&amp;#160; with terms&amp;#160; that represent both long-term and seasonal behaviour of deep-ocean noise, (b) using a statistical model to capture the serial correlation of the residual deviations that are not explained by the functional model, (c) using daily aggregation intervals derived from 1-minute &amp;#160;sound pressure level averages, and (d) applying a non-parametric approach to validate the uncertainties of the trend estimates that avoids the need to make an assumption about the distribution of the residual deviations.&lt;/p&gt;&lt;p&gt;The obtained results show the long term trends vary differently at the four stations. It was observed that low frequency noise generally dominated the significant trends in these oceans. The relative differences between the various statistical levels are remarkably similar for all the frequency bands. Given the complexity of the acoustic environment, it is difficult to identify the main causes of these trends. Some possible explanations for the observed trends are discussed. It was however observed some stations are subjected to strong seasonal variation with a high degree of correlation with climatic factors such as sea surface temperature, Antarctic ice coverage and wind speed. The same seasonal effects is less pronounced in station located closer to the equator.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document