scholarly journals Long-Term Variability of Relationships between Potential Large-Scale Drivers and Summer Precipitation in North China in the CERA-20C Reanalysis

Atmosphere ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 81
Author(s):  
Lan Dai ◽  
Jonathon S. Wright
Keyword(s):  
Twentieth Century ◽  
Large Scale ◽  
North China ◽  
Southern Oscillation ◽  
Summer Precipitation ◽  
Strong Relationship ◽  
Atmospheric Model ◽  
Energy Budgets ◽  
Climate Projections ◽  
Seasonal Forecasts

Although much progress has been made in identifying the large-scale drivers of recent summer precipitation variability in North China, the evolution of these drivers over longer time scales remains unclear. We investigate multidecadal and interannual variability in North China summer precipitation in the 110-year Coupled ECMWF Reanalysis of the Twentieth Century (CERA-20C), considering changes in regional moisture and surface energy budgets along with nine circulation indices linked to anomalous precipitation in this region. The CERA-20C record is separated into three distinct periods according to the running climatology of summer precipitation: 1901–1944 (neutral), 1945–1979 (wet), and 1980–2010 (dry). CERA-20C reproduces expected relationships between large-scale drivers and regional summer precipitation anomalies well during 1980–2010, but these relationships generally do not extend to earlier periods. For example, a strong relationship with the Eurasian teleconnection pattern only emerges in the late 1970s, while correlations with the El Niño-Southern Oscillation and the Pacific–Japan pattern change sign in the mid-twentieth century. We evaluate two possible reasons for this nonstationarity: (1) the underlying atmospheric model may require strong data assimilation constraints to capture large-scale circulation influences on North China, or (2) large-scale drivers inferred from recent records may be less general than expected. Our analysis indicates that both factors contribute to the identified nonstationarity in CERA-20C, with implications for the reliability of seasonal forecasts and climate projections based on current models.

scholarly journals Seasonal Forecasts of the Twentieth Century

2020 ◽  
Vol 101 (8) ◽  
pp. E1413-E1426 ◽  
Author(s):  
Antje Weisheimer ◽  
Daniel J. Befort ◽  
Dave MacLeod ◽  
Tim Palmer ◽  
Chris O’Reilly ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Large Scale ◽  
Seasonal Forecast ◽  
Forecast Skill ◽  
Seasonal Forecasts ◽  
Climate Anomalies ◽  
Global Circulation Models ◽  
Skill Scores ◽  
Physically Based ◽  
Forecast Models

Abstract Forecasts of seasonal climate anomalies using physically based global circulation models are routinely made at operational meteorological centers around the world. A crucial component of any seasonal forecast system is the set of retrospective forecasts, or hindcasts, from past years that are used to estimate skill and to calibrate the forecasts. Hindcasts are usually produced over a period of around 20–30 years. However, recent studies have demonstrated that seasonal forecast skill can undergo pronounced multidecadal variations. These results imply that relatively short hindcasts are not adequate for reliably testing seasonal forecasts and that small hindcast sample sizes can potentially lead to skill estimates that are not robust. Here we present new and unprecedented 110-year-long coupled hindcasts of the next season over the period 1901–2010. Their performance for the recent period is in good agreement with those of operational forecast models. While skill for ENSO is very high during recent decades, it is markedly reduced during the 1930s–1950s. Skill at the beginning of the twentieth century is, however, as high as for recent high-skill periods. Consistent with findings in atmosphere-only hindcasts, a midcentury drop in forecast skill is found for a range of atmospheric fields, including large-scale indices such as the NAO and the PNA patterns. As with ENSO, skill scores for these indices recover in the early twentieth century, suggesting that the midcentury drop in skill is not due to a lack of good observational data. A public dissemination platform for our hindcast data is available, and we invite the scientific community to explore them.

Hadley Cell Widening: Model Simulations versus Observations

2009 ◽  
Vol 22 (10) ◽  
pp. 2713-2725 ◽  
Author(s):  
Celeste M. Johanson ◽  
Qiang Fu
Keyword(s):  
Twentieth Century ◽  
General Circulation ◽  
Large Scale ◽  
General Circulation Models ◽  
Hadley Cell ◽  
Climate Projections ◽  
The West ◽  
Model Simulations ◽  
Stratospheric Cooling ◽  
Future Climate Projections

Abstract Observations show that the Hadley cell has widened by about 2°–5° since 1979. This widening and the concomitant poleward displacement of the subtropical dry zones may be accompanied by large-scale drying near 30°N and 30°S. Such drying poses a risk to inhabitants of these regions who are accustomed to established rainfall patterns. Simple and comprehensive general circulation models (GCMs) indicate that the Hadley cell may widen in response to global warming, warming of the west Pacific, or polar stratospheric cooling. The combination of these factors may be responsible for the recent observations. But there is no study so far that has compared the observed widening to GCM simulations of twentieth-century climate integrated with historical changes in forcings. Here the Hadley cell widening is assessed in current GCMs from historical simulations of the twentieth century as well as future climate projections and preindustrial control runs. The authors find that observed widening cannot be explained by natural variability. This observed widening is also significantly larger than in simulations of the twentieth and twenty-first centuries. These results illustrate the need for further investigation into the discrepancy between the observed and simulated widening of the Hadley cell.

Gridded Statistical Downscaling Based on Interpolation of Parameters and Predictor Locations for Summer Daily Precipitation in North China

2019 ◽  
Vol 58 (10) ◽  
pp. 2295-2311
Author(s):  
Yonghe Liu ◽  
Jinming Feng ◽  
Zongliang Yang ◽  
Yonghong Hu ◽  
Jianlin Li
Keyword(s):  
Distance Function ◽  
Statistical Downscaling ◽  
Spatial Dependence ◽  
Large Scale ◽  
North China ◽  
Dynamical Downscaling ◽  
Daily Precipitation ◽  
Summer Precipitation ◽  
Single Station ◽  
Dense Grid

AbstractFew statistical downscaling applications have provided gridded products that can provide downscaled values for a no-gauge area as is done by dynamical downscaling. In this study, a gridded statistical downscaling scheme is presented to downscale summer precipitation to a dense grid that covers North China. The main innovation of this scheme is interpolating the parameters of single-station models to this dense grid and assigning optimal predictor values according to an interpolated predictand–predictor distance function. This method can produce spatial dependence (spatial autocorrelation) and transmit the spatial heterogeneity of predictor values from the large-scale predictors to the downscaled outputs. Such gridded output at no-gauge stations shows performances comparable to that at the gauged stations. The area mean precipitation of the downscaled results is comparable to other products. The main value of the downscaling scheme is that it can obtain reasonable outputs for no-gauge stations.

scholarly journals Seasonal Contrast in Precipitation Mechanisms over Nepal Deduced from Relationship with the Large-Scale Climate Patterns

2013 ◽  
Vol 13 (1) ◽  
pp. 115-123 ◽  
Author(s):  
Madan Sigdel ◽  
Motoyoshi Ikeda
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Southern Oscillation ◽  
Summer Precipitation ◽  
Walker Circulation ◽  
Moisture Flux ◽  
Rain Gauge ◽  
Western Region ◽  
Eastern Region ◽  
The Relationship

Summer precipitation dominates over winter one for the annual total in south Asia, while the winter condition is still important for agricultural productions. Rain gauge data over Nepal were analyzed with large-scale atmospheric patterns such as El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). In the period of June to September, summer monsoon rainfall over Nepal (SMRN) is generally higher in the eastern region along with a peak in the central region associated with the local orography. Its interannual variability was found to be correlated with the southern oscillation index (SOI): i.e., when La Niña occurs, eastward moisture flux is blocked over Bay of Bengal (BOB) by the anomalous Walker circulation extending from the Pacific. The local-scale condition for higher SMRN is implied by a main moisture route along the eastern arm of the low pressure in northeastern India, as proved by a significant correlation between SMRN and the northward moisture flux. In winter (DJFM), precipitation occurs more in the western region. The higher winter precipitation over Nepal (WPN) was correlated almost equally with positive Dipole Mode Index (DMI) over the Indian Ocean and also SOI, while the relationship with SOI is reversed from summer. A clear linkage was suggested with moisture flux from the Arabian Sea and the further western region. Thus, possible impacts of anomalous precipitation have to be predicted under the relationship with the large-scale indices depending on seasons. Nepal Journal of Science and Technology Vol. 13, No. 1 (2012) 115-123 DOI: http://dx.doi.org/10.3126/njst.v13i1.7450

scholarly journals Climate-Induced Yield Losses for Winter Wheat in Henan Province, North China and Their Relationship with Circulation Anomalies

Water ◽  
2021 ◽  
Vol 13 (23) ◽  
pp. 3341
Author(s):  
Hui Zheng ◽  
Jin Huang ◽  
Jiadong Chen
Keyword(s):  
Winter Wheat ◽  
Large Scale ◽  
North China ◽  
Southern Oscillation ◽  
Assessment Method ◽  
Henan Province ◽  
Western Hemisphere ◽  
Yield Losses ◽  
Yield Data ◽  
Atmospheric Circulation Indices

Risk analysis using climate-induced yield losses (CIYL) extracted from long-term yield data have been recognized in China, but the research focusing on the time-series characteristics of risk and the circulation signals behind yield losses still remains incomplete. To address these challenges, a case study on winter wheat production in Henan province, north China was conducted by using annual series of yield in 17 cities during 1988–2017 and monthly series of 15 types of large-scale oceanic-atmospheric circulation indices (LOACI). A comprehensive risk assessment method was established by combining the intensity, frequency, and variability of CIYL and principal component analysis (PCA). The results showed that the westernmost Henan was identified as the area of higher-risk. PCA and Mann–Kendall trend tests indicated that the southern, northern, eastern, and western areas in Henan province were classified as having different annual CIYL variations in these four sub-regions; the decreasing trend of CIYL in northern area was the most notable. Since the 2000s, a significant decline in CIYL was found in each sub-region. It should be noted that the key LOACI, which includes Tropical Northern Atlantic Index (TNA), Western Hemisphere warm pool (WHWP), and Southern oscillation index (SOI), indicated significant CIYL anomalies in some months. Furthermore, the regional yield simulation results using linear regression for the independent variables of year and various LOACI were satisfactory, with the average relative error ranging from 3.48% to 6.87%.

High vs. low latitude influence on seasonal stratospheric pathways in the atmospheric model ICON

2021 ◽  
Author(s):  
Raphael Köhler ◽  
Dörthe Handorf ◽  
Ralf Jaiser ◽  
Klaus Dethloff
Keyword(s):  
Large Scale ◽  
Arctic Oscillation ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
Atmospheric Model ◽  
The Arctic ◽  
Late Winter ◽  
Stratospheric Polar Vortex ◽  
Enso Events ◽  
Hemisphere Winter

<p>Stratospheric pathways play an important role in connecting distant anomaly patterns to each other on seasonal timescales. As long-lived stratospheric extreme events can influence the large-scale tropospheric circulation on timescales of multiple weeks, stratospheric pathways have been identified as one of the main potential sources for subseasonal to seasonal predictability in mid-latitudes. These pathways have been shown to connect Arctic anomalies to lower latitudes and vice versa. However, there is an ongoing discussion on how strong these stratospheric pathways are and how they exactly work.</p><p> </p><p>In this context, we investigate two strongly discussed stratospheric pathways by analysing a suite of seasonal experiments with the atmospheric model ICON: On the one hand, the effect of El Niño-Southern Oscillation (ENSO) on the stratospheric polar vortex, and thus the circulation in mid and high latitudes in winter. And on the other hand, the effect of a rapidly changing Arctic on lower latitudes via the stratosphere. The former effect is simulated realistically by ICON, and the results from the ensemble simulations suggest that ENSO has an effect on the large-scale Northern Hemisphere winter circulation. The ICON experiments and the reanalysis exhibit a weakened stratospheric vortex in warm ENSO years. Furthermore, in particular in winter, warm ENSO events favour the negative phase of the Arctic Oscillation, whereas cold events favour the positive phase. The ICON simulations also suggest a significant effect of ENSO on the Atlantic-European sector in late winter. Unlike the effect of ENSO, ICON simulations and the reanalysis do not agree on the stratospheric pathway for Arctic-midlatitude linkages. Whereas the reanalysis exhibits a weakening of the stratospheric vortex in midwinter and a connected tropospheric negative Arctic Oscillation circulation response to amplified Arctic warming, this is not the case in the ICON simulations. Implications and potential reasons for this discrepancy are further analysed and discussed in this work.  </p>

The German Climate Forecast System 2.1: seasonal forecast performance over Europe

2021 ◽  
Author(s):  
Kristina Fröhlich ◽  
Katharina Isensee ◽  
Sascha Brandt ◽  
Sebastian Brune ◽  
Andreas Paxian ◽  
...  
Keyword(s):  
Large Scale ◽  
Atmospheric Model ◽  
Prediction Skill ◽  
Climate Forecast ◽  
Seasonal Forecasts ◽  
Max Planck ◽  
Forecast System ◽  
Climate Forecast System ◽  
Forecast Performance ◽  
The Impact

<p>In November 2020, the new version of the German Climate Forecast System, GCFS2.1, became operational at Deutscher Wetterdienst (DWD), providing new seasonal forecasts every month. The system <strong>is based</strong><strong> </strong>on the Max Planck Institute for Meteorology Earth-System Model <strong>(MPI-ESM-HR)</strong> and is developed jointly by DWD, the Max Planck Institute for Meteorology and Universität Hamburg.</p><p>In GCFS2.1, ERA5 and ORAS5 reanalyses are assimilated using atmospheric, oceanic and sea ice nudging, respectively. From the assimilation, 50-member 6-month forecast ensembles are initialized at the start of each month. Prediction skill is assessed with a 30-member 6-month hindcast ensemble covering the time period 1982-2019 for February, May, August and November start months, and 1990-2019 for the remaining start months. Both the forecast and hindcast ensembles are generated by oceanic bred vectors with additional physical perturbations applied to the upper atmospheric model layers.</p><p>Here, we investigate the performance of GCFS2.1 summer and winter forecasts over Europe. While our main focus is on the prediction of large scale patterns that control the weather regimes during these two seasons, e.g. European blockings, special emphasis is paid on the impact of the January 2021 sudden stratospheric warming (SSW) event on the performance of GCFS2.1. The inclusion of the early phases of the January 2021 SSW event in the forecast initialisation significantly changes the GCFS2.1 forecast for February 2021 European surface climate. Prediction skill of GCFS2.1 for summer European blocking events will be also compared to the previous version GCFS2.0.</p>

scholarly journals A global empirical system for probabilistic seasonal climate prediction

2015 ◽  
Vol 8 (12) ◽  
pp. 3947-3973 ◽  
Author(s):  
J. M. Eden ◽  
G. J. van Oldenborgh ◽  
E. Hawkins ◽  
E. B. Suckling
Keyword(s):  
Air Temperature ◽  
Large Scale ◽  
Southern Oscillation ◽  
Surface Air Temperature ◽  
Climate Change Signal ◽  
Seasonal Forecasts ◽  
Physical Relationship ◽  
Skill Scores ◽  
Probabilistic Forecasts ◽  
Empirical System

Abstract. Preparing for episodes with risks of anomalous weather a month to a year ahead is an important challenge for governments, non-governmental organisations, and private companies and is dependent on the availability of reliable forecasts. The majority of operational seasonal forecasts are made using process-based dynamical models, which are complex, computationally challenging and prone to biases. Empirical forecast approaches built on statistical models to represent physical processes offer an alternative to dynamical systems and can provide either a benchmark for comparison or independent supplementary forecasts. Here, we present a simple empirical system based on multiple linear regression for producing probabilistic forecasts of seasonal surface air temperature and precipitation across the globe. The global CO2-equivalent concentration is taken as the primary predictor; subsequent predictors, including large-scale modes of variability in the climate system and local-scale information, are selected on the basis of their physical relationship with the predictand. The focus given to the climate change signal as a source of skill and the probabilistic nature of the forecasts produced constitute a novel approach to global empirical prediction. Hindcasts for the period 1961–2013 are validated against observations using deterministic (correlation of seasonal means) and probabilistic (continuous rank probability skill scores) metrics. Good skill is found in many regions, particularly for surface air temperature and most notably in much of Europe during the spring and summer seasons. For precipitation, skill is generally limited to regions with known El Niño–Southern Oscillation (ENSO) teleconnections. The system is used in a quasi-operational framework to generate empirical seasonal forecasts on a monthly basis.

scholarly journals Global atmospheric response to specific linear combinations of the main SST modes. Part I: numerical experiments and preliminary results

1996 ◽  
Vol 14 (10) ◽  
pp. 1066-1077 ◽  
Author(s):  
S. Trzaska ◽  
V. Moron ◽  
B. Fontaine
Keyword(s):  
Numerical Experiments ◽  
General Circulation ◽  
Large Scale ◽  
Southern Oscillation ◽  
Regional Scale ◽  
Circulation Model ◽  
Atmospheric Model ◽  
Equatorial Atlantic ◽  
Preliminary Results ◽  
The Impact

Abstract. This article investigates through numerical experiments the controversial question of the impact of El Niño-Southern Oscillation (ENSO) phenomena on climate according to large-scale and regional-scale interhemispheric thermal contrast. Eight experiments (two considering only inversed Atlantic thermal anomalies and six combining ENSO warm phase with large-scale interhemispheric contrast and Atlantic anomaly patterns) were performed with the Météo-France atmospheric general circulation model. The definition of boundary conditions from observed composites and principal components is presented and preliminary results concerning the month of August, especially over West Africa and the equatorial Atlantic are discussed. Results are coherent with observations and show that interhemispheric and regional scale sea-surface-temperature anomaly (SST) patterns could significantly modulate the impact of ENSO phenomena: the impact of warm-phase ENSO, relative to the atmospheric model intercomparison project (AMIP) climatology, seems stronger when embedded in global and regional SSTA patterns representative of the post-1970 conditions [i.e. with temperatures warmer (colder) than the long-term mean in the southern hemisphere (northern hemisphere)]. Atlantic SSTAs may also play a significant role.

scholarly journals A 431-Yr Reconstruction of Western Colorado Snowpack from Tree Rings

2003 ◽  
Vol 16 (10) ◽  
pp. 1551-1561 ◽  
Author(s):  
Connie A. Woodhouse
Keyword(s):  
Twentieth Century ◽  
River Basin ◽  
Tree Ring ◽  
Snow Water Equivalent ◽  
Southern Oscillation ◽  
Strong Relationship ◽  
Transitional Zone ◽  
Winter Precipitation ◽  
Winter Climate ◽  
Western Colorado

Abstract A tree-ring-based reconstruction for 1 April snow water equivalent (SWE) is generated for the Gunnison River basin region in western Colorado. The reconstruction explains 63% of the variance in the instrumental record and extends from 1569 to 1999. When the twentieth-century part of the record is compared to the full record, the variability and extremes in the twentieth century appear representative of the long-term record. However, years of extreme SWE (low and high) and persistent low SWE events are not evenly distributed throughout the record. The twentieth century is notable for several periods that lack extreme years, and along with the nineteenth century and the second half of the eighteenth century, contains many fewer persistent low SWE events than the first half of the reconstruction. Low SWE in the western United States is associated with several circulation patterns, including the Pacific–North American (PNA) pattern and those related to El Niño–Southern Oscillation (ENSO), but the Gunnison River basin is on the edge of the area with a strong relationship to the PNA and is generally in a transitional zone with respect to regional ENSO influences. Tree-ring chronologies from Oregon and New Mexico, regions impacted by ENSO, were used as rough proxies of northwestern and southwestern U.S. winter precipitation to explore possible associations between Gunnison SWE and winter climate in these two regions over the past four centuries.

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