scholarly journals Evaluating boreal summer circulation patterns of CMIP6 climate models over the Asian region

2021 ◽  
Author(s):  
Lulei Bu ◽  
Zhiyan Zuo ◽  
Ning An
Keyword(s):  
Climate Models ◽  
Boreal Summer ◽  
Summer Circulation ◽  
Asian Region ◽  
Circulation Patterns

scholarly journals Evaluating Boreal Summer Circulation Patterns of CMIP6 Climate Models Over The Asian Region

2021 ◽  
Author(s):  
Lulei Bu ◽  
Zhiyan Zuo ◽  
Ning An
Keyword(s):  
Extreme Events ◽  
Climate Models ◽  
Model Performance ◽  
Coupled Model ◽  
Boreal Summer ◽  
Self Organizing Map ◽  
Summer Circulation ◽  
Circulation Patterns ◽  
Daily Scale ◽  
Intercomparison Project

Abstract Our confidence in future climate projection depends on the ability of climate models to simulate the current climate, and model performance in simulating atmospheric circulation affects the ability to simulate extreme events. This study uses the self-organizing map (SOM) method to evaluate the frequency, persistence, and transition characteristics of models in the Coupled Model Intercomparison Project Phase 6 (CMIP6) for different ensembles of the 500 hPa daily geopotential height (Z500) in Asia, and then ranks all ensembles according to a comprehensive ranking metric (MR). Our results show that the SOM method is a powerful tool for assessing the daily-scale circulation simulation skills in Asia, and the results are not significantly affected by different map sizes. Positive associations between the performance of ensembles for any two of frequency, persistence, and transition were found, indicating that an ensemble that performs well for one metric is good for the others. The results of the MR ranking show that the r10i1p1f1 ensemble of CanESM5 gives the best overall simulation of 500 hPa circulation in Asia, and this is also the ensemble that best simulates frequency characteristics. The MR simulation skills of the 10 best ensembles for the position of the Western North Pacific Subtropical High (WNPSH) are far better than those of the 10 worst. Such differences may lead to errors in the simulation of extreme events. This study will help future studies in the choice of ensembles with higher circulation simulation skills to improve the credibility of their conclusions.

scholarly journals Sensitivity of boreal-summer circulation and precipitation to atmospheric aerosols in selected regions – Part 1: Africa and India

2009 ◽  
Vol 27 (10) ◽  
pp. 3989-4007 ◽  
Author(s):  
Y. C. Sud ◽  
E. Wilcox ◽  
W. K.-M. Lau ◽  
G. K. Walker ◽  
X.-H. Liu ◽  
...  
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Initial Conditions ◽  
Regional Climate ◽  
Circulation Model ◽  
Climate Simulation ◽  
Boreal Summer ◽  
Summer Circulation ◽  
Precipitation Difference

Abstract. Version-4 of the Goddard Earth Observing System (GEOS-4) General Circulation Model (GCM) was employed to assess the influence of potential changes in aerosols on the regional circulation, ambient temperatures, and precipitation in four selected regions: India and Africa (current paper), as well as North and South America (companion paper). Ensemble-simulations were carried out with the GCM to assess the aerosol direct and indirect effects, hereafter ADE and AIE. Each simulation was started from the NCEP-analyzed initial conditions for 1 May and was integrated through May-June-July-August of each year: 1982–1987 to provide an ensemble set of six simulations. In the first set, called experiment (#1), climatological aerosols were prescribed. The next two experiments (#2 and #3) had two sets of simulations each: one with 2X and other with 1/2X the climatological aerosols over each of the four selected regions. In experiment #2, the anomaly regions were advectively restricted (AR), i.e., the large-scale prognostic fields outside the aerosol anomaly regions were prescribed while in experiment #3, the anomaly regions were advectively Interactive (AI) as is the case in a normal GCM integrations, but with the same aerosols anomalies as in experiment #2. Intercomparisons of circulation, diabatic heating, and precipitation difference fields showed large disparities among the AR and AI simulations, which raised serious questions about the proverbial AR assumption, commonly invoked in regional climate simulation studies. Consequently AI simulation mode was chosen for the subsequent studies. Two more experiments (#4 and #5) were performed in the AI mode in which ADE and AIE were activated one at a time. The results showed that ADE and AIE work in concert to make the joint influences larger than sum of each acting alone. Moreover, the ADE and AIE influences were vastly different for the Indian and Africa regions, which suggest an imperative need to include them rationally in climate models. We also found that the aerosol induced increase of tropical cirrus clouds would potentially offset any cirrus thinning that may occur due to warming in response to CO2 increase.

scholarly journals Interannual variability of the boreal summer tropical UTLS in observations and CCMVal-2 simulations

2016 ◽  
Vol 16 (13) ◽  
pp. 8695-8714 ◽  
Author(s):  
Markus Kunze ◽  
Peter Braesicke ◽  
Ulrike Langematz ◽  
Gabriele Stiller
Keyword(s):  
Climate Models ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Multiple Linear Regression Model ◽  
Transport Processes ◽  
Boreal Summer ◽  
Temperature Pattern ◽  
The Tibetan Plateau ◽  
Quasi Biennial Oscillation ◽  
Mixing Ratios

Abstract. During boreal summer the upper troposphere/lower stratosphere (UTLS) in the Northern Hemisphere shows a distinct maximum in water vapour (H2O) mixing ratios and a coincident minimum in ozone (O3) mixing ratios, both confined within the Asian monsoon anticyclone (AMA). This well-known feature has been related to transport processes emerging above the convective systems during the Asian summer monsoon (ASM), further modified by the dynamics of the AMA. We compare the ability of chemistry–climate models (CCMs) to reproduce the climatological characteristics and variability of H2O, O3, and temperature in the UTLS during the boreal summer with MIPAS satellite observations and ERA-Interim reanalyses. By using a multiple linear regression model the main driving factors, the strength of the ASM, the quasi-biennial oscillation (QBO), and the El Niño–Southern Oscillation (ENSO), are separated. The regression patterns related to ENSO show a coherent, zonally asymmetric signal for temperatures and H2O mixing ratios for ERA-Interim and the CCMs and suggest a weakening of the ASM during ENSO warm events. The QBO modulation of the lower-stratospheric temperature near the Equator is well represented as a zonally symmetric pattern in the CCMs. Changes in H2O and O3 mixing ratios are consistent with the QBO-induced temperature and circulation anomalies but less zonally symmetric than the temperature pattern. Regarding the ASM, the results of the regression analysis show for ERA-Interim and the CCMs enhanced H2O and reduced O3 mixing ratios within the AMA for stronger ASM seasons. The CCM results can further confirm earlier studies which emphasize the importance of the Tibetan Plateau/southern slope of the Himalayas as the main source region for H2O in the AMA. The results suggest that H2O is transported towards higher latitudes at the north-eastern edge of the AMA rather than towards low equatorial latitudes to be fed into the tropical pipe.

scholarly journals Tendency Bias Correction in Coupled and Uncoupled Global Climate Models with a Focus on Impacts over North America

2019 ◽  
Vol 32 (2) ◽  
pp. 639-661 ◽  
Author(s):  
Y. Chang ◽  
S. D. Schubert ◽  
R. D. Koster ◽  
A. M. Molod ◽  
H. Wang
Keyword(s):  
North America ◽  
Bias Correction ◽  
Climate Models ◽  
Global Climate ◽  
Storm Track ◽  
Coupled Model ◽  
Global Climate Models ◽  
Forecast Skill ◽  
Boreal Summer ◽  
Transient Wave

Abstract We revisit the bias correction problem in current climate models, taking advantage of state-of-the-art atmospheric reanalysis data and new data assimilation tools that simplify the estimation of short-term (6 hourly) atmospheric tendency errors. The focus is on the extent to which correcting biases in atmospheric tendencies improves the model’s climatology, variability, and ultimately forecast skill at subseasonal and seasonal time scales. Results are presented for the NASA GMAO GEOS model in both uncoupled (atmosphere only) and coupled (atmosphere–ocean) modes. For the uncoupled model, the focus is on correcting a stunted North Pacific jet and a dry bias over the central United States during boreal summer—long-standing errors that are indeed common to many current AGCMs. The results show that the tendency bias correction (TBC) eliminates the jet bias and substantially increases the precipitation over the Great Plains. These changes are accompanied by much improved (increased) storm-track activity throughout the northern midlatitudes. For the coupled model, the atmospheric TBCs produce substantial improvements in the simulated mean climate and its variability, including a much reduced SST warm bias, more realistic ENSO-related SST variability and teleconnections, and much improved subtropical jets and related submonthly transient wave activity. Despite these improvements, the improvement in subseasonal and seasonal forecast skill over North America is only modest at best. The reasons for this, which are presumably relevant to any forecast system, involve the competing influences of predictability loss with time and the time it takes for climate drift to first have a significant impact on forecast skill.

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.

scholarly journals The last interglacial (Eemian) climate simulated by LOVECLIM and CCSM3

2012 ◽  
Vol 8 (5) ◽  
pp. 5293-5340 ◽  
Author(s):  
I. Nikolova ◽  
Q. Yin ◽  
A. Berger ◽  
U. K. Singh ◽  
M. P. Karami
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Hydrological Cycle ◽  
The Arctic ◽  
Boreal Summer ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Proxy Data ◽  
Vegetation Feedback ◽  
Depth Analysis

Abstract. This paper presents a detailed analysis of the climate of the last interglacial simulated by two climate models of different complexities, LOVECLIM and CCSM3. The simulated surface temperature, hydrological cycle, vegetation and ENSO variability during the last interglacial are analyzed through the comparison with the simulated Pre-Industrial (PI) climate. In both models, the last interglacial period is characterized by a significant warming (cooling) over almost all the continents during boreal summer (winter) leading to a largely increased (reduced) seasonal contrast in the northern (southern) hemisphere. This is mainly due to the much higher (lower) insolation received by the whole Earth in boreal summer (winter) during this interglacial. The arctic is warmer than PI through the whole year, resulting from its much higher summer insolation and its remnant effect in the following fall-winter through the interactions between atmosphere, ocean and sea ice. In the tropical Pacific, the change in the SST annual cycle is suggested to be related to a minor shift towards an El Nino, slightly stronger for MIS-5 than for PI. Intensified African monsoon and vegetation feedback are responsible for the cooling during summer in North Africa and Arabian Peninsula. Over India precipitation maximum is found further west, while in Africa the precipitation maximum migrates further north. Trees and grassland expand north in Sahel/Sahara. A mix of forest and grassland occupies continents and expand deep in the high northern latitudes. Desert areas reduce significantly in Northern Hemisphere, but increase in North Australia. The simulated large-scale climate change during the last interglacial compares reasonably well with proxy data, giving credit to both models and reconstructions. However, discrepancies exist at some regional scales between the two models, indicating the necessity of more in depth analysis of the models and comparisons with proxy data.

scholarly journals The Role of Synoptic Cyclones for the Formation of Arctic Summer Circulation Patterns as Clustered by Self-Organizing Maps

Atmosphere ◽  
2019 ◽  
Vol 10 (8) ◽  
pp. 474 ◽  
Author(s):  
Min-Hee Lee ◽  
Joo-Hong Kim
Keyword(s):  
Arctic Ocean ◽  
Large Scale ◽  
The Arctic ◽  
Cyclone Activity ◽  
Summer Circulation ◽  
Self Organizing Maps ◽  
Weather Patterns ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Self Organizing

Contribution of extra-tropical synoptic cyclones to the formation of mean summer atmospheric circulation patterns in the Arctic domain (≥60° N) was investigated by clustering dominant Arctic circulation patterns based on daily mean sea-level pressure using self-organizing maps (SOMs). Three SOM patterns were identified; one pattern had prevalent low-pressure anomalies in the Arctic Circle (SOM1), while two exhibited opposite dipoles with primary high-pressure anomalies covering the Arctic Ocean (SOM2 and SOM3). The time series of their occurrence frequencies demonstrated the largest inter-annual variation in SOM1, a slight decreasing trend in SOM2, and the abrupt upswing after 2007 in SOM3. Analyses of synoptic cyclone activity using the cyclone track data confirmed the vital contribution of synoptic cyclones to the formation of large-scale patterns. Arctic cyclone activity was enhanced in the SOM1, which was consistent with the meridional temperature gradient increases over the land–Arctic ocean boundaries co-located with major cyclone pathways. The composite daily synoptic evolution of each SOM revealed that all three SOMs persisted for less than five days on average. These evolutionary short-term weather patterns have substantial variability at inter-annual and longer timescales. Therefore, the synoptic-scale activity is central to forming the seasonal-mean climate of the Arctic.

scholarly journals Regional temperature and precipitation changes under high-end (≥4 ° C) global warming

2011 ◽  
Vol 369 (1934) ◽  
pp. 85-98 ◽  
Author(s):  
M. G. Sanderson ◽  
D. L. Hemming ◽  
R. A. Betts
Keyword(s):  
Climate Change ◽  
Climate Changes ◽  
Climate Models ◽  
First Century ◽  
Boreal Summer ◽  
Large Temperature ◽  
Boreal Winter ◽  
Global Average ◽  
Global Rate ◽  
Twenty First Century

Climate models vary widely in their projections of both global mean temperature rise and regional climate changes, but are there any systematic differences in regional changes associated with different levels of global climate sensitivity? This paper examines model projections of climate change over the twenty-first century from the Intergovernmental Panel on Climate Change Fourth Assessment Report which used the A2 scenario from the IPCC Special Report on Emissions Scenarios, assessing whether different regional responses can be seen in models categorized as ‘high-end’ (those projecting 4 ° C or more by the end of the twenty-first century relative to the preindustrial). It also identifies regions where the largest climate changes are projected under high-end warming. The mean spatial patterns of change, normalized against the global rate of warming, are generally similar in high-end and ‘non-high-end’ simulations. The exception is the higher latitudes, where land areas warm relatively faster in boreal summer in high-end models, but sea ice areas show varying differences in boreal winter. Many continental interiors warm approximately twice as fast as the global average, with this being particularly accentuated in boreal summer, and the winter-time Arctic Ocean temperatures rise more than three times faster than the global average. Large temperature increases and precipitation decreases are projected in some of the regions that currently experience water resource pressures, including Mediterranean fringe regions, indicating enhanced pressure on water resources in these areas.

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