Subjects -> METEOROLOGY (Total: 106 journals)
 Showing 1 - 36 of 36 Journals sorted alphabetically Acta Meteorologica Sinica       (Followers: 4) Advances in Atmospheric Sciences       (Followers: 42) Advances in Climate Change Research       (Followers: 59) Advances in Meteorology       (Followers: 23) Advances in Statistical Climatology, Meteorology and Oceanography       (Followers: 11) Aeolian Research       (Followers: 7) Agricultural and Forest Meteorology       (Followers: 20) American Journal of Climate Change       (Followers: 41) Atmósfera       (Followers: 2) Atmosphere       (Followers: 33) Atmosphere-Ocean       (Followers: 15) Atmospheric and Oceanic Science Letters       (Followers: 9) Atmospheric Chemistry and Physics (ACP)       (Followers: 43) Atmospheric Chemistry and Physics Discussions (ACPD)       (Followers: 14) Atmospheric Environment       (Followers: 72) Atmospheric Environment : X       (Followers: 3) Atmospheric Research       (Followers: 71) Atmospheric Science Letters       (Followers: 39) Boundary-Layer Meteorology       (Followers: 29) Bulletin of Atmospheric Science and Technology       (Followers: 5) Bulletin of the American Meteorological Society       (Followers: 62) Carbon Balance and Management       (Followers: 6) Ciencia, Ambiente y Clima       (Followers: 1) Climate       (Followers: 6) Climate and Energy       (Followers: 7) Climate Change Economics       (Followers: 50) Climate Change Responses       (Followers: 27) Climate Dynamics       (Followers: 44) Climate Law       (Followers: 7) Climate of the Past (CP)       (Followers: 7) Climate of the Past Discussions (CPD)       (Followers: 1) Climate Policy       (Followers: 56) Climate Research       (Followers: 8) Climate Resilience and Sustainability       (Followers: 29) Climate Risk Management       (Followers: 12) Climate Services       (Followers: 4) Climatic Change       (Followers: 71) Current Climate Change Reports       (Followers: 22) Dynamics and Statistics of the Climate System       (Followers: 6) Dynamics of Atmospheres and Oceans       (Followers: 18) Earth Perspectives - Transdisciplinarity Enabled       (Followers: 1) Economics of Disasters and Climate Change       (Followers: 17) Energy & Environment       (Followers: 26) Environmental and Climate Technologies       (Followers: 3) Environmental Dynamics and Global Climate Change       (Followers: 24) Frontiers in Climate       (Followers: 4) GeoHazards       (Followers: 2) Global Meteorology       (Followers: 17) International Journal of Atmospheric Sciences       (Followers: 24) International Journal of Biometeorology       (Followers: 3) International Journal of Climate Change Strategies and Management       (Followers: 33) International Journal of Climatology       (Followers: 28) International Journal of Environment and Climate Change       (Followers: 24) International Journal of Image and Data Fusion       (Followers: 3) Journal of Agricultural Meteorology Journal of Applied Meteorology and Climatology       (Followers: 42) Journal of Atmospheric and Oceanic Technology       (Followers: 33) Journal of Atmospheric and Solar-Terrestrial Physics       (Followers: 164) Journal of Atmospheric Chemistry       (Followers: 23) Journal of Climate       (Followers: 55) Journal of Climate Change       (Followers: 25) Journal of Climate Change and Health       (Followers: 6) Journal of Climatology       (Followers: 3) Journal of Economic Literature       (Followers: 19) Journal of Hydrology and Meteorology       (Followers: 39) Journal of Hydrometeorology       (Followers: 9) Journal of Integrative Environmental Sciences       (Followers: 4) Journal of Meteorological Research       (Followers: 3) Journal of Meteorology and Climate Science       (Followers: 19) Journal of Space Weather and Space Climate       (Followers: 30) Journal of the Atmospheric Sciences       (Followers: 79) Journal of the Meteorological Society of Japan       (Followers: 7) Journal of Weather Modification       (Followers: 3) Mediterranean Marine Science       (Followers: 2) Meteorologica       (Followers: 2) Meteorological Applications       (Followers: 4) Meteorological Monographs       (Followers: 1) Meteorologische Zeitschrift       (Followers: 4) Meteorology and Atmospheric Physics       (Followers: 28) Mètode Science Studies Journal : Annual Review Michigan Journal of Sustainability       (Followers: 1) Modeling Earth Systems and Environment       (Followers: 1) Monthly Notices of the Royal Astronomical Society       (Followers: 14) Monthly Weather Review       (Followers: 29) Nature Climate Change       (Followers: 153) Nature Reports Climate Change       (Followers: 40) Nīvār       (Followers: 1) npj Climate and Atmospheric Science       (Followers: 4) Open Atmospheric Science Journal       (Followers: 4) Open Journal of Modern Hydrology       (Followers: 5) Oxford Open Climate Change       (Followers: 6) Revista Iberoamericana de Bioeconomía y Cambio Climático       (Followers: 1) Russian Meteorology and Hydrology       (Followers: 3) Space Weather       (Followers: 27) Studia Geophysica et Geodaetica       (Followers: 1) Tellus A       (Followers: 21) Tellus B       (Followers: 20) The Cryosphere (TC)       (Followers: 8) The Quarterly Journal of the Royal Meteorological Society       (Followers: 31) Theoretical and Applied Climatology       (Followers: 13) Tropical Cyclone Research and Review       (Followers: 1) Urban Climate       (Followers: 4) Weather and Climate Dynamics       (Followers: 1) Weather and Climate Extremes       (Followers: 17) Weather and Forecasting       (Followers: 42) Weatherwise       (Followers: 18) 气候与环境研究       (Followers: 2)
Similar Journals
 Climate DynamicsJournal Prestige (SJR): 2.445 Citation Impact (citeScore): 4Number of Followers: 44      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1432-0894 - ISSN (Online) 0930-7575 Published by Springer-Verlag  [2469 journals]
• Erratum to: Seasonality and time scale dependence of the relationship
between turbulent surface heat flux and SST

PubDate: 2022-11-01

• Drying tendency over the southern slope of the Tibetan Plateau in recent
decades: role of a CGT-like atmospheric change

Abstract: Abstract A significant drying tendency over the southern slope of the Tibetan Plateau (SSTP) in summer (especially in July–September) during 1980–2018 is identified in this study. Moisture budget analysis reveals that the drying tendency is dominated by a decreased vertical moisture advection due to weakened upward motion, which is mainly resulted from an anticyclonic trend appeared over the northeastern TP. This anomalous anticyclone can weaken the upper-tropospheric divergence pumping over the SSTP. In addition, moist static energy diagnosis indicates that the southern branch of the anomalous anticyclone advects low moist enthalpy air into the SSTP, which also suppresses local upward motion and convection. Moreover, the anticyclonic trend over the northeastern TP is found not a local phenomenon, but is rather associated with the large-scale atmospheric change in the middle latitudes that shows a circumglobal teleconnection (CGT)-like pattern. Our results highlight that the long-term CGT-like trend of atmospheric circulation plays a crucial role in triggering the drying tendency over the SSTP in recent decades.
PubDate: 2022-11-01

• Surface and atmospheric patterns for early and late rainy season onset
years in South America

Abstract: Abstract The biosphere–atmosphere interactions associated with the rainy season onset in South America (SA) are not well understood. This study aimed to analyze the atmospheric and surface patterns associated with early, neutral, and late rainy season onset in tropical regions of SA. The following years represented each rainy season onset: 1998, 2006, 2009 (early), 2001, 2004, 2005 (neutral), 2000, 2007, 2008 (late). The early (late) onset were negative (positive) rainy season onset date anomalies in comparison to the climatological mean (1998–2016) over central SA. Distinct atmospheric conditions were identified in the early and late rainy season onset. In the early onset, the northwesterly moisture flux and moisture advection were higher than average over central-east SA, where the precipitation increased. In the late onset, precipitation was enhanced in northwest SA and the configuration of multiple atmospheric blocking episodes contributed to delay the rainy season onset. Surface conditions also contributed to both the early/late rainy season onset. In the early onset, wetter and cooler pre-onset conditions over the central-east SA were verified. In the late onset, surface conditions were dry and warm before onset. Even though the atmospheric instability was promoted by the increase in sensible heating, dry atmospheric conditions were not favorable to deep convection, thus delaying the onset. These findings highlight how the onset variability promotes different atmospheric and surface patterns in SA. The results will contribute to the development of weather and climate models to better represent the rainy season onset focusing on biosphere–atmosphere processes improvements.
PubDate: 2022-11-01

• The combined influence of the stratospheric polar vortex and ENSO on zonal
asymmetries in the southern hemisphere upper tropospheric circulation
during austral spring and summer

Abstract: Abstract The influence of El Niño Southern Oscillation (ENSO) and the Stratospheric Polar Vortex (SPV) on the zonal asymmetries in the Southern Hemisphere atmospheric circulation during spring and summer is examined. The main objective of the work is to explore if the SPV can modulate the ENSO teleconnections in the extratropics. We use a large ensemble of seasonal hindcasts from the European Centre for Medium-Range Weather Forecasts Integrated Forecast System to provide a much larger sample size than is possible from the observations alone. We find a small but statistically significant relationship between ENSO and the SPV, with El Niño events occurring with weak SPV and La Niña events occurring with strong SPV more often than expected by chance, in agreement with previous works. We show that the zonally asymmetric response to ENSO and SPV can be mainly explained by a linear combination of the response to both forcings, and that they can combine constructively or destructively. However the nature of this interference evolves through the spring and summer period, and is not aligned with the traditional seasons. From this perspective, we find that the tropospheric asymmetries in response to ENSO are more intense when El Niño events occur with weak SPV and La Niña events occur with strong SPV, at least from September through December. In the stratosphere, the ENSO teleconnections are mostly confounded by the SPV signal. The analysis of Rossby Wave Source and of wave activity shows that both are stronger when El Niño events occur together with weak SPV, and when La Niña events occur together with strong SPV.
PubDate: 2022-11-01

• Why coupled general circulation models overestimate the ENSO and Indian
Summer Monsoon Rainfall (ISMR) relationship'

Abstract: Abstract Interannual variability of the Indian Summer Monsoon Rainfall (ISMR) is modulated by Sea Surface Temperature (SST) anomalies over Indo-Pacific Oceans, especially by the El Niño Southern Oscillation (ENSO). In general, coupled models used for seasonal prediction overestimate the correlation between ENSO and ISMR compared to observations. By analysing the observational data from 1982 to 2017, this study shows that the relationship between ENSO and ISMR is weak during August compared to the other months of the summer monsoon season (June, July, and September). This weak association between ENSO and ISMR during August is due to an increase in the synoptic variability. Thus, the effect of large-scale flow dominated by ENSO is suppressed by the formation of a synoptic system in the Bay of Bengal (BoB), making ENSO-ISMR relation feeble in August. The data analysis of various coupled models shows that all models underestimate synoptic variability, due to which simulated ENSO-ISMR relation is overestimated during August. Coupled model exhibit strong biases in relative humidity and cyclonic circulation over the northern BoB hence underestimating the synoptic variability.
PubDate: 2022-11-01

• On the added value of statistical post-processing of regional climate
models to identify homogeneous patterns of summer rainfall anomalies in
Germany

Abstract: Abstract A fuzzy classification scheme that results in physically interpretable meteorological patterns associated with rainfall generation is applied to classify homogeneous regions of boreal summer rainfall anomalies in Germany. Four leading homogeneous regions are classified, representing the western, southeastern, eastern, and northern/northwestern parts of Germany with some overlap in the central parts of Germany. Variations of the sea level pressure gradient across Europe, e.g., between the continental and maritime regions, is the major phenomenon that triggers the time development of the rainfall regions by modulating wind patterns and moisture advection. Two regional climate models (REMO and CCLM4) were used to investigate the capability of climate models to reproduce the observed summer rainfall regions. Both regional climate models (RCMs) were once driven by the ERA-Interim reanalysis and once by the MPI-ESM general circulation model (GCM). Overall, the RCMs exhibit good performance in terms of the regionalization of summer rainfall in Germany; though the goodness-of-match with the rainfall regions/patterns from observational data is low in some cases and the REMO model driven by MPI-ESM fails to reproduce the western homogeneous rainfall region. Under future climate change, virtually the same leading modes of summer rainfall occur, suggesting that the basic synoptic processes associated with the regional patterns remain the same over Germany. We have also assessed the added value of bias-correcting the MPI-ESM driven RCMs using a simple linear scaling approach. The bias correction does not significantly alter the identification of homogeneous rainfall regions and, hence, does not improve their goodness-of-match compared to the observed patterns, except for the one case where the original RCM output completely fails to reproduce the observed pattern. While the linear scaling method improves the basic statistics of precipitation, it does not improve the simulated meteorological patterns represented by the precipitation regimes.
PubDate: 2022-11-01

• Assessing free tropospheric quasi-equilibrium for different GCM
resolutions using a cloud-resolving model simulation of tropical
convection

Abstract: Abstract This study examines the free-tropospheric quasi-equilibrium at different global climate model (GCM) resolutions using the simulation of tropical convection by a cloud-resolving model during the Tropical Western Pacific International Cloud Experiment. The simulated dynamic and thermodynamic fields within the model domain are averaged over subdomains of different sizes equivalent to different GCM resolutions. These coarse-grained fields are then used to compute CAPE and its change with time, and their relationships with simulated convection. Results show that CAPE change with time is controlled predominantly by variations of thermodynamic properties in the planetary boundary layer for all subdomain sizes ranging from 64 to 4 km. Lag correlation analysis shows that CAPE generation by the free-tropospheric dynamical advection (dCAPEls) leads convective precipitation but is in phase with convective mass flux at 600 mb and 500 mb vertical velocity for all subdomain sizes. However, the correlation coefficients and regression slopes decrease as the subdomain size decreases for subdomain sizes smaller than 16 km. This is probably due to increased randomness of convection and more scale-dependence of the relationships when the subdomain size reaches the grey zone. By examining the sensitivity of the relationships of convection with dCAPEls to temporal scales in different subdomain size, it shows that the quasi-equilibrium between dCAPEls and convection holds well for timescales of 30 min or longer at all subdomain sizes. These results suggest that the free tropospheric quasi-equilibrium assumption may still be useable even for GCM resolutions in the grey zone.
PubDate: 2022-11-01

• Impacts of planetary boundary layer parameterization in RegCM4.7 on the
intensity and structure of simulated tropical cyclones over the
Philippines

Abstract: Abstract The influence of planetary boundary layer (PBL) parameterization on tropical cyclones (TCs) over the Philippine region is examined using the Holtslag and the University of Washington (UW) schemes in RegCM4.7 at 25-km resolution. Comparisons made between the model-simulated TCs and best track data indicate that more TCs were reproduced in both the RegCM4.7 simulations than the ERA-Interim reanalysis. It is further revealed that while only small biases were obtained in the number of TCs detected from the two RegCM4.7 simulations, only the UW scheme was able to simulate strong (Category 4–Category 5) TCs. A composite analysis on the radial cross section of azimuthally averaged wind fields shows that the UW scheme generates stronger wind velocities with narrower and elevated maximum tangential wind, and enhances low-level momentum convergence, compared with the Holtslag scheme. In addition, the radial positioning of the strong diabatic heating of UW simulation within the radius of maximum wind supported the needed conditions for warmer core formation and contributed to the enhancement of the secondary circulation by vertical advection of high absolute angular momentum, hence the higher intensity of TCs. The resulting higher surface maximum winds with increased diabatic heating within the eyewall and stronger warm-core structures in the UW simulation suggest that the induced convergence has offset the dissipative effects of momentum loss more than that in the Holtslag run.
PubDate: 2022-11-01

• High-resolution modelling of climatic hazards relevant for Canada’s
northern transportation sector

Abstract: Abstract Infrastructure and transportation systems on which northern communities rely are exposed to a variety of climatic hazards over a broad range of scales. Efforts to adapt these systems to the rapidly warming Arctic climate require high-quality climate projections. Here, a state-of-the-art regional climate model is used to perform simulations at 4-km resolution over the eastern and central Canadian Arctic. These include, for the first time over this region, high-resolution climate projections extending to the year 2040. Validation shows that the model adequately simulates base climate variables, as well as variables hazardous to northern engineering and transportation systems, such as degrading permafrost, extreme rainfall, and extreme wind gust. Added value is found over coarser resolution simulations. A novel approach integrating climate model output and machine learning is used for deriving fog—an important, but complex hazard. Hotspots of change to climatic hazards over the next two decades (2021–2040) are identified. These include increases to short-duration rainfall intensity extremes exceeding 50%, suggesting Super–Clausius–Clapeyron scaling. Increases to extreme wind gust pressure are projected to reach 25% over some regions, while widespread increases in active layer thickness and ground temperature are expected. Overall fog frequency is projected to increase by around 10% over most of the study region by 2040, due to increasing frequency of high humidity conditions. Given that these changes are projected to be already underway, urgent action is required to successfully adapt northern transportation and engineering systems located in regions where the magnitude of hazards is projected to increase.
PubDate: 2022-11-01

• Combined signatures of atmospheric drivers, soil moisture, and moisture
source on floods in Narmada River basin, India

Abstract: Abstract Floods in India affect millions of people during the summer monsoon (June–September) every year. Atmospheric factors, land surface conditions, and moisture source and pathways ride a combined signature in producing floods in rain-fed river basins. However, floods in Indian river basins are mostly studied considering the role of extreme precipitation, and critical contribution of factors related to land and atmosphere is often neglected. Using the Narmada River basin in central India as a testbed, we investigated the combined signature of extreme precipitation, soil moisture, and moisture sources on floods in the basin during 1951–2018 period. We find that most of the high-flow events in the basin occur during August and September and, about 80% of them are caused by extreme precipitation combined with higher antecedent soil moisture. The major flood producing storms in the Narmada basin are linked with high amount of vertically integrated water vapor flux, low mean sea level pressure, and strong winds. The Arabian Sea is the primary moisture source for the flood producing storms. However, previously unrecognized north Indian plain is also a dominant source of flood producing storms in the basin during the mid and late monsoon season. The moisture recycled from land-surface predominates the moisture sources of storm events in the upstream sub-basins while the contribution of moisture from the Arabian Sea is higher in the downstream sub-basins. These combined linkages of land, ocean and atmosphere, can assist in developing skillful early flood warning system for the Indian river basins.
PubDate: 2022-11-01

• Impact of air–sea coupling on the simulation of Indian summer monsoon
using a high-resolution Regional Earth System Model over CORDEX-SA

Abstract: Abstract A new high-resolution Regional Earth System Model, namely ROM, has been implemented over CORDEX-SA towards examining the impact of air–sea coupling on the Indian summer monsoon characteristics. ROM's simulated mean ISM rainfall and associated dynamical and thermodynamical processes, including the representation of northward and eastward propagating convention bands, are closer to observation than its standalone atmospheric model component (REMO), highlighting the advantage of air–sea coupling. However, the value addition of air–sea coupling varies spatially with more significant improvements over regions with large biases. Bay of Bengal and the eastern equatorial Indian Ocean are the most prominent region where the highest added value is observed with a significant reduction up to 50–500% precipitation bias. Most of the changes in precipitation over the ocean are associated with convective precipitation (CP) due to the suppression of convective activity caused by the negative feedback due to the inclusion of air–sea coupling. However, CP and large-scale precipitation (LP) improvements show east–west asymmetry over the Indian land region. The substantial LP bias reduction is noticed over the wet bias region of western central India due to its suppression, while enhanced CP over eastern central India contributed to the reduction of dry bias. An insignificant change is noticed over Tibetan Plateau, northern India, and Indo Gangetic plains. The weakening of moisture-laden low-level Somalia Jets causes the diminishing of moisture supply from the Arabian Sea (AS) towards Indian land regions resulting in suppressed precipitation, reducing wet bias, especially over western central India. The anomalous high kinetic energy over AS, wind shear, and tropospheric temperature gradient in REMO compared to observation is substantially reduced in the ROM, facilitating the favourable condition for suppressing moisture feeding and hence the wet bias over west-central India in ROM. The warmer midlatitude in ROM than REMO over eastern central India strengthens the convection, enhancing precipitation results in reducing the dry bias. Despite substantially improved ROM’performance, it still exhibits some systematic biases (wet/dry) partially associated with the persistent warm/cold SST bias and land–atmosphere interaction.
PubDate: 2022-11-01

• Future climate projections for Eastern Canada

Abstract: Abstract Recent global warming has caused significant changes to the regional climate over Eastern Canada and brought unprecedented challenges to the local communities, such as rising sea level, shrinking sea ice coverage, increasing coastal and inland floods, accelerated coastal erosion, and so on. Although local governments have declared climate emergency in recent years, there is still a lack of real climate actions due to the poor understanding of the future climatic changes over Eastern Canada and how to mitigate and adapt to those changes from a long-term perspective. Here we attempt to fill this gap by developing high-resolution regional climate scenarios for Eastern Canada throughout the twenty-first century under three greenhouse gases emission scenarios (RCP2.6—low, RCP4.5—medium, and RCP8.5—high). The results suggest that the low-emission scenario of RCP2.6 would potentially stabilize the regional climate (i.e., no significant changes in both temperature and precipitation) over Eastern Canada after the continuous warming reaches its peak in the middle of this century. However, an average warming about 1 °C would still be expected from now to the end of this century under RCP2.6, highlighting the importance of preparing for a new climate normal even though strict carbon reduction efforts could be made before 2050. In comparison, both RCP4.5 and RCP8.5 scenarios would lead to a continuous warming over Eastern Canada with increased total precipitation throughout this century. Most importantly, the warming trend under RCP8.5 is likely to accelerate after 2050, which would potentially cause significant shifts in the precipitation seasonality and bring more climate extremes, such as droughts in August, increasing spring and fall floods, more freezing rains between fall and winter, and more heavy snowfalls in winter. The results from this study can help the local policy makers understand the importance and scientific implications of taking immediate carbon reduction actions and developing long-term climate adaptation plans.
PubDate: 2022-11-01

• Atmosphere-driven cold SST biases over the western North Pacific in the
GloSea5 seasonal forecast system

Abstract: Abstract The predictability of the sea surface temperature (SST) in seasonal forecast systems is crucial for accurate seasonal predictions. In this study, we evaluated the prediction of SST in the Global Seasonal forecast system version 5 (GloSea5) hindcast, particularly focusing on the western North Pacific (WNP), where the SST can modify atmospheric convection and the East Asian weather. GloSea5 has a cold SST bias in the WNP that grows over at least 7 months. The bias originates from the surface net heat flux. At the beginning of model integration, the ocean receives excessive heat from the atmosphere because of the predominant positive bias in the downward shortwave radiation (SW), which rapidly decreased within a few days as cloud cover builds. Then, the negative bias in the latent heat (LH) flux increases over time and induces a negative bias in the surface net heat flux. Although the magnitude of the negative bias in LH flux gradually decreases, it remains the most significant contributor to the negative bias in the net heat flux bias for more than 250 days. Uncoupled ocean model experiments showed that the ocean model is unlikely to be the primary source of the SST bias.
PubDate: 2022-11-01

• Recent enhancement and prolonged occurrence of MJO over the Indian Ocean
and their impact on Indian summer monsoon rainfall

Abstract: Abstract The Madden–Julian oscillation (MJO) is one of the leading modes of tropical intra-seasonal variability, which exerts significant impacts on the weather and climate across the globe, particularly in the tropics. MJO affects the Asian monsoon by producing enhanced and suppressed convection during the active and break periods, respectively. In the recent decades, the heat content of Indo-western Pacific Ocean has increased significantly, which strengthened the MJO activity. Previous studies also have shown that the expansion of Indo-western Pacific warm pool led to the warping of MJO life cycle, which decreases its residence time over the Indian Ocean (IO) and increases over the Pacific Ocean. Here we show that in the boreal summer months, MJO amplitude has strengthened during the global warming hiatus or rapid IO warming period (1999–2015) compared to the previous period (1982–1998). In the later period, MJO exhibits a faster regeneration over the western IO, and its residence time has increased in the western hemisphere and western IO but decreased in the eastern IO and eastern Pacific Ocean. The strengthening of MJO and the readjustment in its residence time are due to the local MJO feedback on the IO and the La Nina like sea surface temperature pattern in the Pacific Ocean. The prolonged MJO activity leads to bursts of rainfall over the Indian subcontinent in Phase 3 and Phase 4, influencing the active spells of the Indian summer monsoon and causing heavy rainfall over central India and East Asia.
PubDate: 2022-11-01

• Understanding rainfall prediction skill over the Sahel in NMME seasonal
forecast

Abstract: Abstract Sahelian rainfall presents large interannual variability which is partly controlled by the sea surface temperature anomalies (SSTa) over the eastern Mediterranean, equatorial Pacific and Atlantic oceans, making seasonal prediction of rainfall changes in Sahel potentially possible. However, it is not clear whether seasonal forecast models present skill to predict the Sahelian rainfall anomalies. Here, we consider the set of models from the North American Multi-model ensemble (NMME) and analyze their skill in predicting the Sahelian precipitation and address the sources of this skill. Results show that though the skill in predicting the Sahelian rainfall is generally low, it can be mostly explained by a combination of how well models predict the SSTa in the Mediterranean and in the equatorial Pacific regions, and how well they simulate the teleconnections of these SSTa with Sahelian rainfall. Our results suggest that Sahelian rainfall skill is improved for those models in which the Pacific SST—Sahel rainfall teleconnection is correctly simulated. On the other hand, models present a good ability to reproduce the sign of the Mediterranean SSTa—Sahel teleconnection, albeit with underestimated amplitude due to an underestimation of the variance of the SSTa over this oceanic region. However, they fail to correctly predict the SSTa over this basin, which is the main reason for the poor Sahel rainfall skill in models. Therefore, results suggest models need to improve their ability to reproduce the variability of the SSTa over the Mediterranean as well as the teleconnections of Sahelian rainfall with Pacific and Mediterranean SSTa.
PubDate: 2022-11-01

• Reassessing the relative role of anthropogenic aerosols and natural
decadal variability in driving the mid-twentieth century global
“cooling”: a focus on the latitudinal gradient of tropospheric
temperature

Abstract: Abstract The global mean surface temperature cooled slightly in the mid-twentieth century despite a continuous increase in greenhouse gas concentrations. The cooling was strongest in the Northern Hemisphere mid-latitudes, while the Southern Hemisphere mid-latitudes experienced moderate warming. This apparent contradiction is often attributed to internal multi-decadal variability originating from Pacific and Atlantic ocean-atmosphere interactions. Given the rapid increase of industrial activities in North America and Europe during that period, it is also plausible that anthropogenic aerosol (AA) emissions (as an external forcing) contributed to the stronger Northern Hemisphere cooling. This paper aims to quantify the contributions of AA and decadal variability to the 1948–1978 cooling. We analyzed the latitudinal temperature trend asymmetry in 60° S–60° N throughout the troposphere, using multiple reanalysis datasets and the Coupled Model Intercomparison Project phase 5 (CMIP5) multi-model ensemble that bears significant similarity with the observed patterns. We show that both AA increase and the North Atlantic Variability Index (NAVI) transition into its negative phase are the major contributors to the latitudinal asymmetry of cooling. At the surface level, based on the horizontal pattern correlation method, AA and NAVI have similar contribution fractions (20 vs. 16%), but the contribution fraction of AA is much larger at 500 hPa (55 vs. 8%). Attributions based on vertical pattern correlation and latitudinal gradient show consistent results. Natural forcings (NAT) also contribute to the cooling asymmetry during mid-20C, but with a much smaller impact compared to AA and NAVI. Therefore, we argue that previous studies that mostly focused on surface variables may have underestimated the role of AA in the mid-twentieth-century climate change. The study suggests that the three-dimensional thermal structure and atmospheric circulation change should be closely examined in future climate attribution analysis.
PubDate: 2022-11-01

• Could detection and attribution of climate change trends be spurious
regression'

Abstract: Since the 1970s, scientists have developed statistical methods intended to formalize detection of changes in global climate and to attribute such changes to relevant causal factors, natural and anthropogenic. Detection and attribution (D&A) of climate change trends is commonly performed using a variant of Hasselmann’s “optimal fingerprinting” method, which involves a linear regression of historical climate observations on corresponding output from numerical climate models. However, it has long been known in the field of time series analysis that regressions of “non-stationary” or “trending” variables are, in general, statistically inconsistent and often spurious. When non-stationarity is caused by “integrated” processes, as is likely the case for climate variables, consistency of least-squares estimators depends on “cointegration” of regressors. This study has shown, using an idealized linear-response-model framework, that if standard assumptions hold then the optimal fingerprinting estimator is consistent, and hence robust against spurious regression. In the case of global mean surface temperature (GMST), parameterizing abstract linear response models in terms of energy balance provides this result with physical interpretability. Hypothesis tests conducted using observations of historical GMST and simulation output from 13 CMIP6 general circulation models produced no evidence that standard assumptions required for consistency were violated. It is therefore concluded that, at least in the case of GMST, detection and attribution of climate change trends is very likely not spurious regression. Furthermore, detection of significant cointegration between observations and model output indicates that the least-squares estimator is “superconsistent”, with better convergence properties than might previously have been assumed. Finally, a new method has been developed for quantifying D&A uncertainty, exploiting the notion of cointegration to eliminate the need for pre-industrial control simulations.
PubDate: 2022-11-01

• East Asian summer monsoon enhanced by COVID-19

Abstract: Abstract Anthropogenic emissions decreased dramatically during the COVID-19 pandemic, but its possible effect on monsoon is unclear. Based on coupled models participating in the COVID Model Intercomparison Project (COVID-MIP), we show modeling evidence that the East Asian summer monsoon (EASM) is enhanced by 2.2% in terms of precipitation and by 5.4% in terms of the southerly wind at lower troposphere, and the amplitude of the forced response reaches about 1/3 of the standard deviation for interannual variability. The enhanced EASM during COVID-19 pandemic is a fast response to reduced aerosols, which is confirmed by the simulated response to the removal of all anthropogenic aerosols. The observational evidence, i.e., the anomalously strong EASM observed in 2020 and 2021, also supports the simulated enhancement of EASM. The essential mechanism for the enhanced EASM in response to COVID-19 is the enhanced zonal thermal contrast between Asian continent and the western North Pacific in the troposphere, due to the reduced aerosol concentration over Asian continent and the associated latent heating feedback. As the enhancement of EASM is a fast response to the reduction in aerosols, the effect of COVID-19 on EASM dampens soon after the rebound of emissions based on the models participating in COVID-MIP.
PubDate: 2022-11-01

• Extreme austral winter precipitation events over the South-American
Altiplano: regional atmospheric features

Abstract: Abstract The South American Altiplano has a marked dry season during the austral winter (June to August, JJA). However, during this season synoptic meteorological conditions triggering heavy precipitation can damage socioeconomic activities, often causing the loss of human lives. Using daily in-situ precipitation data from 39 rain-gauge stations over the northern Altiplano ( $$18^{\circ }\hbox {S}$$ - $$15^{\circ }\hbox {S}$$ ; $$> 3000$$ m.a.s.l.) for the JJA season, we computed the historical percentile 90 (p90) and we identified extreme rainy days with precipitation higher than p90 in the 1980–2010 period. We identified 100 winter extreme precipitation events (WEPEs) over this region that can last between one to 16 days. The K-means analysis was applied to anomalies of geopotential height at 500 hPa from ERA-Interim data during the initial day or Day(0) of WEPEs lasting 1 day (42 cases), 2 days (19) and more than 2 days (39). We found 59 WEPEs characterized by an upper-level trough over the Peruvian-Chilean coast. At 850 hPa, these 59 WEPEs are also associated with cold surges along the eastern Central Andes, indicating an association between the upper-level trough and the cold surge in developing deep convection over the northern Altiplano. A lead-lag composite analysis further showed a significant lower- and mid-tropospheric moistening over the western Amazon 2 days before the onset of these 59 WEPEs, due to low-level northerly wind anomalies originating over equatorial South America. The other 41 WEPEs are associated with a low-level southerly wind regime crossing the equator and a mid-and upper-level low-pressure system over the Peruvian-Chilean coast. While the low-level southerly regime enhances mid-tropospheric moisture transport from the equator towards the Altiplano due to the developed shallow meridional circulation when propagating equatorward, a low-pressure system promotes intensification of upward motion, boosting the upslope moisture transport from the lowlands to the east of the Central Andes towards the Altiplano.
PubDate: 2022-11-01

• Convection-permitting modeling strategies for simulating extreme rainfall
events over Southeastern South America

Abstract: Abstract A set of six convection-permitting (CP) domain configurations were implemented to perform 72-hour long simulations of three extreme precipitation events over Southeastern South America (SESA). The goal of the study is to determine the most adequate configuration for reproducing not only the rainfall evolution and intensity, but also the synoptic triggering mechanisms that led to these extreme events, taking into account the trade-off between model performance and computational cost. This study assesses the impact of (1) the horizontal resolution in the CP domain, (2) the horizontal resolution of the driver domain, (3) the size of both CP and driver domains and (4) the nesting strategy (one-step versus two-step nesting). Each simulation was performed with the Weather Research and Forecasting model driven by the ERA-Interim reanalysis. For each event and domain configuration, a 6-member physics ensemble is built, making a total of 36 simulations for each event. No significant differences were found between the 4 km and 2.4 km CP ensembles. Increasing the horizontal resolution of the driver domain from 20 km to 12 km introduced only subtle differences. Increasing the size of the CP domain improved the model performance, probably because of better resolved topography and, hence, better resolved synoptic environment. The results in this study reveal that the one-step nesting CP ensemble at 4 km horizontal resolution covering an area of $$29^\circ$$ x $$21^\circ$$ (lon-lat) arises as the optimal domain configuration among these tested to simulate extreme precipitation events over SESA.
PubDate: 2022-11-01

JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762