Benefits of CMIP5 Multimodel Ensemble in Reconstructing Historical Ocean Subsurface Temperature Variations

2016 ◽  
Vol 29 (15) ◽  
pp. 5393-5416 ◽  
Author(s):  
Lijing Cheng ◽  
Jiang Zhu
Keyword(s):  
Decadal Variability ◽  
Heat Content ◽  
Coupled Model ◽  
Mapping Method ◽  
Optimal Interpolation ◽  
Cmip5 Models ◽  
Subsurface Temperature ◽  
Sea Level Changes ◽  
Multimodel Ensemble

Abstract A complete map of the ocean subsurface temperature is essential for monitoring aspects of climate change such as the ocean heat content (OHC) and sea level changes and for understanding the dynamics of the ocean/climate variation. However, global observations have not been available in the past, so a mapping strategy is required to fill the data gaps. In this study, an advanced mapping method is proposed to reconstruct the historical ocean subsurface (0–700 m) temperature field from 1940 to 2014 by using ensemble optimal interpolation with a dynamic ensemble (EnOI-DE) approach and a multimodel ensemble of phase 5 of the Coupled Model Intercomparison Project (CMIP5) historical and representative concentration pathway 4.5 simulations. The reconstructed field is a combination of two parts: a first guess provided by the ensemble mean of CMIP5 models and an adjustment by minimizing the analysis error with the assistance of error covariance determined by the CMIP5 models. The uncertainty of the field can also be assessed. This new approach was evaluated using a series of tests, including subsample tests by using data from the Argo period, idealized tests by specifying a truth field from the models, and withdrawn-data tests by removing 20% of the observations for validation. In addition, the authors showed that the ocean mean state, long-term trends, and interannual and decadal variability are all well represented. Furthermore, the most significant benefit of this method is to provide an improved estimate of the long-term historical OHC changes since 1940, which have important implications for Earth’s energy budget.

The Double-ITCZ Bias in CMIP6 Models

2020 ◽  
Author(s):  
Baijun Tian
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Coupled Model ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
Tropical Precipitation ◽  
Double Itcz ◽  
Intercomparison Project ◽  
Fully Coupled

<p>The double-Intertropical Convergence Zone (ITCZ) bias is one of the most outstanding problems in climate models. This study seeks to examine the double-ITCZ bias in the latest state-of-the-art fully coupled global climate models that participated in Coupled Model Intercomparison Project (CMIP) Phase 6 (CMIP6) in comparison to their previous generations (CMIP3 and CMIP5 models). To that end, we have analyzed the long-term annual mean tropical precipitation distributions and several precipitation bias indices that quantify the double-ITCZ biases in 75 climate models including 24 CMIP3 models, 25 CMIP3 models, and 26 CMIP6 models. We find that the double-ITCZ bias and its big inter-model spread persist in CMIP6 models but the double-ITCZ bias is slightly reduced from CMIP3 or CMIP5 models to CMIP6 models.</p>

scholarly journals Evaluation of Temperature and Precipitation Trends and Long-Term Persistence in CMIP5 Twentieth-Century Climate Simulations

2013 ◽  
Vol 26 (12) ◽  
pp. 4168-4185 ◽  
Author(s):  
Sanjiv Kumar ◽  
Venkatesh Merwade ◽  
James L. Kinter ◽  
Dev Niyogi
Keyword(s):  
Twentieth Century ◽  
Climate Models ◽  
Coupled Model ◽  
Research Unit ◽  
Trend Detection ◽  
Climatic Research Unit ◽  
Multimodel Ensemble ◽  
Temperature And Precipitation ◽  
Precipitation Trends

Abstract The authors have analyzed twentieth-century temperature and precipitation trends and long-term persistence from 19 climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5). This study is focused on continental areas (60°S–60°N) during 1930–2004 to ensure higher reliability in the observations. A nonparametric trend detection method is employed, and long-term persistence is quantified using the Hurst coefficient, taken from the hydrology literature. The authors found that the multimodel ensemble–mean global land–average temperature trend (0.07°C decade−1) captures the corresponding observed trend well (0.08°C decade−1). Globally, precipitation trends are distributed (spatially) at about zero in both the models and in the observations. There are large uncertainties in the simulation of regional-/local-scale temperature and precipitation trends. The models’ relative performances are different for temperature and precipitation trends. The models capture the long-term persistence in temperature reasonably well. The areal coverage of observed long-term persistence in precipitation is 60% less (32% of land area) than that of temperature (78%). The models have limited capability to capture the long-term persistence in precipitation. Most climate models underestimate the spatial variability in temperature trends. The multimodel ensemble–average trend generally provides a conservative estimate of local/regional trends. The results of this study are generally not biased by the choice of observation datasets used, including Climatic Research Unit Time Series 3.1; temperature data from Hadley Centre/Climatic Research Unit, version 4; and precipitation data from Global Historical Climatology Network, version 2.

scholarly journals Changing Expendable Bathythermograph Fall Rates and Their Impact on Estimates of Thermosteric Sea Level Rise

2008 ◽  
Vol 21 (21) ◽  
pp. 5657-5672 ◽  
Author(s):  
Susan E. Wijffels ◽  
Josh Willis ◽  
Catia M. Domingues ◽  
Paul Barker ◽  
Neil J. White ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Decadal Variability ◽  
Heat Content ◽  
Time History ◽  
Global Ocean ◽  
Fall Rate ◽  
Rate Minimum ◽  
Fall Rates

Abstract A time-varying warm bias in the global XBT data archive is demonstrated to be largely due to changes in the fall rate of XBT probes likely associated with small manufacturing changes at the factory. Deep-reaching XBTs have a different fall rate history than shallow XBTs. Fall rates were fastest in the early 1970s, reached a minimum between 1975 and 1985, reached another maximum in the late 1980s and early 1990s, and have been declining since. Field XBT/CTD intercomparisons and a pseudoprofile technique based on satellite altimetry largely confirm this time history. A global correction is presented and applied to estimates of the thermosteric component of sea level rise. The XBT fall rate minimum from 1975 to 1985 appears as a 10-yr “warm period” in the global ocean in thermosteric sea level and heat content estimates using uncorrected data. Upon correction, the thermosteric sea level curve has reduced decadal variability and a larger, steadier long-term trend.

scholarly journals An evaluation of CMIP5 precipitation simulations using ground observations over ten river basins in China

2021 ◽  
Author(s):  
Xiuqin Yang ◽  
Bin Yong ◽  
Zhiguo Yu ◽  
Yuqing Zhang
Keyword(s):  
Coupled Model ◽  
Single Mode ◽  
River Basins ◽  
Cmip5 Models ◽  
Multimodel Ensemble ◽  
Intercomparison Project ◽  
Precipitation Indices ◽  
Improved Performance ◽  
Model Ensembles ◽  
Statistical Metrics

Abstract Using the precipitation measurements obtained from 2,419 ground meteorological stations over China from 1960 to 2005 as benchmark, the performance of 21 single-mode precipitation data from the Coupled Model Intercomparison Project Phase 5 (CMIP5) were evaluated using Taylor diagrams and several statistical metrics. Based on statistical metrics, the models were ranked in terms of their ability to reproduce similar patterns in precipitation relative to the observations. Except in Southeast and Pearl river basins, research results show that all model ensemble means overestimate in the rest of the river basins, especially in Southwest and Northwest. The performance of CMIP5 models is quite different among each river basin; most models show significant overestimation in Northwest and Yellow and significant underestimations in Southeast and Pearl. The simulations are more reliable in Songhua, Liao, Yangtze, and Pearl than in other river basins according to spatial distribution and interannual variability. No individual model performs well in all the river basins both spatially and temporally. In Songhua, Liao, Yangtze, and Pearl, precipitation indices are more consistent with observations, and the spread among models is smaller. The multimodel ensemble selected from the most reasonable models indicates improved performance relative to all model ensembles.

scholarly journals Reply to “Comment on ‘Comparison of Low-Frequency Internal Climate Variability in CMIP5 Models and Observations’”

2017 ◽  
Vol 30 (23) ◽  
pp. 9773-9782 ◽  
Author(s):  
Anson H. Cheung ◽  
Michael E. Mann ◽  
Byron A. Steinman ◽  
Leela M. Frankcombe ◽  
Matthew H. England ◽  
...  
Keyword(s):  
Low Frequency ◽  
Coupled Model ◽  
Internal Variability ◽  
Cmip5 Models ◽  
Multimodel Ensemble ◽  
Internal Climate Variability ◽  
Instrumental Record ◽  
Ensemble Mean ◽  
Intercomparison Project ◽  
The Individual

In a comment on a 2017 paper by Cheung et al., Kravtsov states that the results of Cheung et al. are invalidated by errors in the method used to estimate internal variability in historical surface temperatures, which involves using the ensemble mean of simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to estimate the forced signal. Kravtsov claims that differences between the forced signals in the individual models and as defined by the multimodel ensemble mean lead to errors in the assessment of internal variability in both model simulations and the instrumental record. Kravtsov proposes a different method, which instead uses CMIP5 models with at least four realizations to define the forced component. Here, it is shown that the conclusions of Cheung et al. are valid regardless of whether the method of Cheung et al. or that of Kravtsov is applied. Furthermore, many of the points raised by Kravtsov are discussed in Cheung et al., and the disagreements of Kravtsov appear to be mainly due to a misunderstanding of the aims of Cheung et al.

scholarly journals Cold Tongue and Warm Pool ENSO Events in CMIP5: Mean State and Future Projections

2014 ◽  
Vol 27 (8) ◽  
pp. 2861-2885 ◽  
Author(s):  
Andréa S. Taschetto ◽  
Alexander Sen Gupta ◽  
Nicolas C. Jourdain ◽  
Agus Santoso ◽  
Caroline C. Ummenhofer ◽  
...  
Keyword(s):  
Southern Oscillation ◽  
Heat Content ◽  
Coupled Model ◽  
Warm Pool ◽  
Cmip5 Models ◽  
Cold Tongue ◽  
Future Projections ◽  
Enso Events ◽  
Almost All ◽  
Sst Anomalies

Abstract The representation of the El Niño–Southern Oscillation (ENSO) under historical forcing and future projections is analyzed in 34 models from the Coupled Model Intercomparison Project phase 5 (CMIP5). Most models realistically simulate the observed intensity and location of maximum sea surface temperature (SST) anomalies during ENSO events. However, there exist systematic biases in the westward extent of ENSO-related SST anomalies, driven by unrealistic westward displacement and enhancement of the equatorial wind stress in the western Pacific. Almost all CMIP5 models capture the observed asymmetry in magnitude between the warm and cold events (i.e., El Niños are stronger than La Niñas) and between the two types of El Niños: that is, cold tongue (CT) El Niños are stronger than warm pool (WP) El Niños. However, most models fail to reproduce the asymmetry between the two types of La Niñas, with CT stronger than WP events, which is opposite to observations. Most models capture the observed peak in ENSO amplitude around December; however, the seasonal evolution of ENSO has a large range of behavior across the models. The CMIP5 models generally reproduce the duration of CT El Niños but have biases in the evolution of the other types of events. The evolution of WP El Niños suggests that the decay of this event occurs through heat content discharge in the models rather than the advection of SST via anomalous zonal currents, as seems to occur in observations. No consistent changes are seen across the models in the location and magnitude of maximum SST anomalies, frequency, or temporal evolution of these events in a warmer world.

Testing the Trade Wind Charging Mechanism and Its Influence on ENSO Variability

2020 ◽  
Vol 33 (17) ◽  
pp. 7391-7411
Author(s):  
Soumi Chakravorty ◽  
Renellys C. Perez ◽  
Bruce T. Anderson ◽  
Benjamin S. Giese ◽  
Sarah M. Larson ◽  
...  
Keyword(s):  
North Pacific ◽  
Heat Content ◽  
Coupled Model ◽  
Equatorial Pacific ◽  
Trade Wind ◽  
Westerly Wind ◽  
Subsurface Temperature ◽  
Temperature Anomalies ◽  
Fully Coupled ◽  
Sst Anomalies

AbstractDuring the positive phase of the North Pacific Oscillation, westerly wind anomalies over the subtropical North Pacific substantially increase subsurface heat content along the equator by “trade wind charging” (TWC). TWC provides a direct pathway between extratropical atmospheric circulation and El Niño–Southern Oscillation (ENSO) initiation. Previous model studies of this mechanism lacked the ocean–atmospheric coupling needed for ENSO growth, so it is crucial to examine whether TWC-induced heat content anomalies develop into ENSO events in a coupled model. Here, coupled model experiments, forced with TWC favorable (+TWC) or unfavorable (−TWC) wind stress, are used to examine the ENSO response to TWC. The forcing is imposed on the ocean component of the model through the first winter and then the model evolves in a fully coupled configuration through the following winter. The +TWC (−TWC) forcing consistently charges (discharges) the equatorial Pacific in spring and generates positive (negative) subsurface temperature anomalies. These subsurface temperature anomalies advect eastward and upward along the equatorial thermocline and emerge as like-signed sea surface temperature (SST) anomalies in the eastern Pacific, creating favorable conditions upon which coupled air–sea feedback can act. During the fully coupled stage, warm SST anomalies in +TWC forced simulations are amplified by coupled feedbacks and lead to El Niño events. However, while −TWC forcing results in cool SST anomalies, pre-existing warm SST anomalies in the far eastern equatorial Pacific persist and induce local westerly wind anomalies that prevent consistent development of La Niña conditions. While the TWC mechanism provides adequate equatorial heat content to fuel ENSO development, other factors also play a role in determining whether an ENSO event develops.

scholarly journals Attributing Causes of 2015 Record Minimum Sea-Ice Extent in the Sea of Okhotsk

2017 ◽  
Vol 30 (12) ◽  
pp. 4693-4703 ◽  
Author(s):  
Seungmok Paik ◽  
Seung-Ki Min ◽  
Yeon-Hee Kim ◽  
Baek-Min Kim ◽  
Hideo Shiogama ◽  
...  
Keyword(s):  
Sea Ice ◽  
Sea Of Okhotsk ◽  
Coupled Model ◽  
Internal Variability ◽  
Cmip5 Models ◽  
External Forcing ◽  
Sea Ice Extent ◽  
The Sea Of Okhotsk ◽  
The North

In 2015, the sea ice extent (SIE) over the Sea of Okhotsk (Okhotsk SIE) hit a record low since 1979 during February–March, the period when the sea ice extent generally reaches its annual maximum. To quantify the role of anthropogenic influences on the changes observed in Okhotsk SIE, this study employed a fraction of attributable risk (FAR) analysis to compare the probability of occurrence of extreme Okhotsk SIE events and long-term SIE trends using phase 5 of the Coupled Model Intercomparison Project (CMIP5) multimodel simulations performed with and without anthropogenic forcing. It was found that because of anthropogenic influence, both the probability of extreme low Okhotsk SIEs that exceed the 2015 event and the observed long-term trends during 1979–2015 have increased by more than 4 times (FAR = 0.76 to 1). In addition, it is suggested that a strong negative phase of the North Pacific Oscillation (NPO) during midwinter (January–February) 2015 also contributed to the 2015 extreme SIE event. An analysis based on multiple linear regression was conducted to quantify relative contributions of the external forcing (anthropogenic plus natural) and the NPO (internal variability) to the observed SIE changes. About 56.0% and 24.7% of the 2015 SIE anomaly was estimated to be attributable to the external forcing and the strong negative NPO influence, respectively. The external forcing was also found to explain about 86.1% of the observed long-term SIE trend. Further, projections from the CMIP5 models indicate that a sea ice–free condition may occur in the Sea of Okhotsk by the late twenty-first century in some models.

scholarly journals Evaluation of Downscaled CMIP5 Coupled with VIC Model for Flash Drought Simulation in a Humid Subtropical Basin, China

2018 ◽  
Vol 31 (3) ◽  
pp. 1075-1090 ◽  
Author(s):  
Yuqing Zhang ◽  
Qinglong You ◽  
Changchun Chen ◽  
Jing Ge ◽  
Muhammad Adnan
Keyword(s):  
Heat Waves ◽  
Coupled Model ◽  
Cmip5 Models ◽  
Atmospheric Conditions ◽  
Multimodel Ensemble ◽  
Infiltration Capacity ◽  
Coupled Models ◽  
Vic Model ◽  
Ensemble Mean ◽  
Meteorological Observations

Abstract Compared to traditional drought events, flash droughts evolve rapidly during short-term extreme atmospheric conditions, with a lasting period of one pentad to several weeks. There are two main categories of flash droughts: the heat wave flash drought (HWFD), which is mainly caused by persistent high temperatures (heat waves), and the precipitation deficit flash drought (PDFD), which is mainly triggered by precipitation deficits. The authors’ previous research focused on the characteristics and causes of flash drought based on meteorological observations and Variable Infiltration Capacity (VIC) model simulations in a humid subtropical basin (Gan River basin, China). In this study, the authors evaluated the downscaled phase 5 of the Coupled Model Intercomparison Project (CMIP5) models’ simulations, coupled with the VIC model (CMIP5–VIC) in reproducing flash droughts in a humid subtropical basin in China. Most downscaled CMIP5–VIC simulations can reproduce the spatial patterns of flash droughts with respect to the benchmarks. The coupled models fail to readily replicate interannual variation (interannual pentad change), but most models can reflect the interannual variability (temporal standard deviation) and long-term average pentads of flash droughts. It is difficult to simultaneously depict both the spatial and temporal features of flash droughts within only one coupled model. The climatological patterns of the best multimodel ensemble mean are close to those of the all-model ensemble mean, but the best multimodel ensemble mean has a minimal bias range and relatively low computational burden.

A new mode of decadal variability in the Tropical Indian Ocean subsurface temperature and its association with heat redistribution

2021 ◽  
Author(s):  
Sandeep Mohapatra ◽  
Chellappan Gnanaseelan
Keyword(s):  
Indian Ocean ◽  
Wind Stress ◽  
Decadal Variability ◽  
Surface Wind ◽  
Heat Content ◽  
Tropical Indian Ocean ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Subsurface Temperature ◽  
Wind Stress Curl

<p>Similar to the Pacific and Atlantic, Tropical Indian Ocean (TIO) has its own internal climate mode of variabilities such as Indian Ocean Dipole (IOD) and subsurface mode (SSM). A typical interannual SSM is characterized by the meridional gradient in opposing subsurface temperature anomalies in the eastern equatorial IO and in the southwestern IO. Here in the present study, we have explored the structure and the underlying dynamics for the SSM in decadal time scale which has not been reported before. By analyzing different reanalysis products we observe that decadal SSM is characterized by a pure north-south pattern with the northern mode covering the entire equatorial belt which is different from interannual SSM. A north-south SSM is the leading mode of decadal variability in the thermocline and subsurface temperature over the TIO. Our preliminary analysis suggests that the decadal variability in the surface winds along the equatorial IO and the associated wind stress curl are found to be the primary forcing mechanisms for the decadal evolution of the north-south mode. Positive wind stress curl anomalies south of 8<sup>o</sup>S intensify the downwelling Rossby waves in the south during the positive phase of the decadal SSM. On the other hand, the northern cooling is driven mostly by the equatorial upwelling Kelvin waves and the Ekman divergence. Further, the phase transition in the SSM is primarily determined by the strength of the surface wind and the associated Ekman transport. The equatorial easterlies (westerlies) diverge (converge) the meridional Ekman transport, transporting heat towards the off-equatorial (equatorial) region during the positive (negative) phase. Consistently with SSM, upper 500m oceanic heat content reveals a conventional north-south dipole highlighting the importance of SSM on the TIO heat redistribution. This is further supported by the modulation of meridional overturning circulation and the meridional heat balance across the southern Indian Ocean (SIO). Overall the present study explores the underlying mechanism responsible for decadal SSM and its association with the heat distribution across the SIO.</p>

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