scholarly journals Internal Atmospheric Variability and Interannual-to-Decadal ENSO Variability in a CGCM

2009 ◽  
Vol 22 (9) ◽  
pp. 2335-2355 ◽  
Author(s):  
Sang-Wook Yeh ◽  
Ben P. Kirtman
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
General Circulation Models ◽  
Tropical Pacific ◽  
Frequency Noise ◽  
Atmospheric Variability ◽  
Enso Variability ◽  
Ensemble Strategy ◽  
The Tropics ◽  
The Impact

Abstract The interactive ensemble coupling strategy has been developed specifically to determine how noise due to internal atmosphere dynamics impacts climate variability within the context of coupled general circulation models (CGCMs). In this study the authors investigate the impact of internal atmospheric variability on the ENSO variability using four CGCM simulations. In the control simulation, the interactive ensemble strategy is applied globally, thereby reducing the noise at the air–sea interface at each ocean grid point. In the second and third CGCM simulations, the interactive ensemble strategy is applied locally in the extratropics versus the tropics only, respectively. In addition, those results were compared with a standard CGCM. The results suggest that tropical internal atmospheric variability strengthens the interannual-to-decadal ENSO variability and leads to a broader spectral peak. However, the noise due to internal atmospheric dynamics plays different roles when the interannual and decadal ENSO variability is considered separately. There are noise-induced changes in the SST–zonal wind stress feedbacks from interannual to decadal time scales. The tropical atmospheric internal variability largely modifies the frequency as opposed to the amplitude of the ENSO variability on interannual time scales. In contrast, tropical internal atmospheric variability is effective in forcing decadal ENSO variability, resulting in a significant decrease of decadal ENSO amplitude in the central tropical Pacific in a CGCM when the noise is reduced. The authors argue that the decadal ENSO variability is directly affected by the low-frequency noise over the western part of the tropical Pacific in a linear sense. On the other hand, the impact of extratropical atmospheric noise on the ENSO variability is weaker than the noise in the tropics.

scholarly journals The Southern Hemisphere semiannual oscillation and circulation variability during the Mid-Holocene

2010 ◽  
Vol 6 (4) ◽  
pp. 415-430 ◽  
Author(s):  
D. Ackerley ◽  
J. A. Renwick
Keyword(s):  
Southern Hemisphere ◽  
General Circulation ◽  
General Circulation Models ◽  
Atmospheric Variability ◽  
Climatic Effects ◽  
Orbital Parameters ◽  
Ocean General Circulation Models ◽  
Intercomparison Project ◽  
The Tropics ◽  
Semiannual Oscillation

Abstract. The Paleoclimate Modelling Intercomparison Project (PMIP) was undertaken to assess the climatic effects of the presence of large ice-sheets and changes in the Earth's orbital parameters in fully coupled Atmosphere-Ocean General Circulation Models (AOGCMs). Much of the previous literature has focussed on the tropics and the Northern Hemisphere during the last glacial maximum and Mid-Holocene whereas this study focuses only on the Southern Hemisphere. This study addresses the representation of the Semiannual Oscillation (SAO) in the PMIP2 models and how it may have changed during the Mid-Holocene. The output from the five models suggest a weakening of the (austral) autumn circumpolar trough (CPT) and (in all but one model) a strengthening of the spring CPT. The effects of changing the orbital parameters are to cause warming and drying during spring over New Zealand and a cooling and moistening during autumn. The amount of spring warming/drying and autumn cooling/moistening is variable between the models and depends on the climatological locations of surface pressure anomalies associated with changes in the SAO. This study also undertakes an Empirical Orthogonal Function (EOF) analysis of the leading modes of atmospheric variability during the control and Mid-Holocene phases for each model. Despite the seasonal changes, the overall month by month and interannual variability was simulated to have changed little from the Mid-Holocene to present.

scholarly journals The Southern Hemisphere semiannual oscillation and circulation variability during the Mid-Holocene

2010 ◽  
Vol 6 (1) ◽  
pp. 185-224 ◽  
Author(s):  
D. Ackerley ◽  
J. A. Renwick
Keyword(s):  
Southern Hemisphere ◽  
General Circulation ◽  
General Circulation Models ◽  
Atmospheric Variability ◽  
Climatic Effects ◽  
Orbital Parameters ◽  
Ocean General Circulation Models ◽  
Intercomparison Project ◽  
The Tropics ◽  
Semiannual Oscillation

Abstract. The Paleoclimate Modelling Intercomparison Project (PMIP) was undertaken to assess the climatic effects of the presence of large ice-sheets and changes in the Earth's orbital parameters in fully coupled Atmosphere-Ocean General Circulation Models (AOGCMs). Much of the previous literature has focussed on the tropics and the Northern Hemisphere during the last glacial maximum and Mid-Holocene whereas this study focuses only on the Southern Hemisphere. This study addresses the representation of the Semiannual Oscillation (SAO) in the PMIP2 models and how it may have changed during the Mid-Holocene. The output from the models suggest a weakening of the (austral) autumn circumpolar trough (CPT) and (in all but one model) a strengthening of the spring CPT. The effects of changing the orbital parameters are to cause warming and drying during spring over New Zealand and a cooling and moistening during autumn. The amount of spring warming/drying and autumn cooling/moistening is variable between the models and depends on the climatological locations of surface pressure anomalies associated with changes in the SAO. This study also undertakes an Empirical Orthogonal Function (EOF) analysis of the leading modes of atmospheric variability during the control and Mid-Holocene phases for each model. Despite the seasonal changes, the overall month by month and interannual variability was simulated to have changed little from the Mid-Holocene to present.

Comparison and Sensitivity of ODASI Ocean Analyses in the Tropical Pacific

2007 ◽  
Vol 135 (6) ◽  
pp. 2242-2264 ◽  
Author(s):  
Chaojiao Sun ◽  
Michele M. Rienecker ◽  
Anthony Rosati ◽  
Matthew Harrison ◽  
Andrew Wittenberg ◽  
...  
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Tropical Pacific ◽  
Global Ocean ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Salinity Treatment ◽  
Salinity Field ◽  
Significant Difference ◽  
The Impact ◽  
The Tropical Pacific

Abstract Two global ocean analyses from 1993 to 2001 have been generated by the Global Modeling and Assimilation Office (GMAO) and Geophysical Fluid Dynamics Laboratory (GFDL), as part of the Ocean Data Assimilation for Seasonal-to-Interannual Prediction (ODASI) consortium efforts. The ocean general circulation models (OGCM) and assimilation methods in the analyses are different, but the forcing and observations are the same as designed for ODASI experiments. Global expendable bathythermograph and Tropical Atmosphere Ocean (TAO) temperature profile observations are assimilated. The GMAO analysis also assimilates synthetic salinity profiles based on climatological T–S relationships from observations (denoted “TS scheme”). The quality of the two ocean analyses in the tropical Pacific is examined here. Questions such as the following are addressed: How do different assimilation methods impact the analyses, including ancillary fields such as salinity and currents? Is there a significant difference in interpretation of the variability from different analyses? How does the treatment of salinity impact the analyses? Both GMAO and GFDL analyses reproduce the time mean and variability of the temperature field compared with assimilated TAO temperature data, taking into account the natural variability and representation errors of the assimilated temperature observations. Surface zonal currents at 15 m from the two analyses generally agree with observed climatology. Zonal current profiles from the analyses capture the intensity and variability of the Equatorial Undercurrent (EUC) displayed in the independent acoustic Doppler current profiler data at three TAO moorings across the equatorial Pacific basin. Compared with independent data from TAO servicing cruises, the results show that 1) temperature errors are reduced below the thermocline in both analyses; 2) salinity errors are considerably reduced below the thermocline in the GMAO analysis; and 3) errors in zonal currents from both analyses are comparable. To discern the impact of the forcing and salinity treatment, a sensitivity study is undertaken with the GMAO assimilation system. Additional analyses are produced with a different forcing dataset, and another scheme to modify the salinity field is tested. This second scheme updates salinity at the time of temperature assimilation based on model T–S relationships (denoted “T scheme”). The results show that both assimilated field (i.e., temperature) and fields that are not directly observed (i.e., salinity and currents) are impacted. Forcing appears to have more impact near the surface (above the core of the EUC), while the salinity treatment is more important below the surface that is directly influenced by forcing. Overall, the TS scheme is more effective than the T scheme in correcting model bias in salinity and improving the current structure. Zonal currents from the GMAO control run where no data are assimilated are as good as the best analysis.

Successive Modulation of ENSO to the Future Greenhouse Warming

2008 ◽  
Vol 21 (1) ◽  
pp. 3-21 ◽  
Author(s):  
Soon-Il An ◽  
Jong-Seong Kug ◽  
Yoo-Geun Ham ◽  
In-Sik Kang
Keyword(s):  
General Circulation ◽  
Southern Oscillation ◽  
General Circulation Models ◽  
Tropical Pacific ◽  
Greenhouse Warming ◽  
Delayed Response ◽  
Subsurface Temperature ◽  
Climate System Model ◽  
The Mean ◽  
The Tropical Pacific

Abstract The multidecadal modulation of the El Niño–Southern Oscillation (ENSO) due to greenhouse warming has been analyzed herein by means of diagnostics of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled general circulation models (CGCMs) and the eigenanalysis of a simplified version of an intermediate ENSO model. The response of the global-mean troposphere temperature to increasing greenhouse gases is more likely linear, while the amplitude and period of ENSO fluctuates in a multidecadal time scale. The climate system model outputs suggest that the multidecadal modulation of ENSO is related to the delayed response of the subsurface temperature in the tropical Pacific compared to the response time of the sea surface temperature (SST), which would lead a modulation of the vertical temperature gradient. Furthermore, an eigenanalysis considering only two parameters, the changes in the zonal contrast of the mean background SST and the changes in the vertical contrast between the mean surface and subsurface temperatures in the tropical Pacific, exhibits a good agreement with the CGCM outputs in terms of the multidecadal modulations of the ENSO amplitude and period. In particular, the change in the vertical contrast, that is, change in difference between the subsurface temperature and SST, turns out to be more influential on the ENSO modulation than changes in the mean SST itself.

Tropical Atmospheric Variability Forced by Oceanic Internal Variability

2007 ◽  
Vol 20 (4) ◽  
pp. 765-771 ◽  
Author(s):  
Markus Jochum ◽  
Clara Deser ◽  
Adam Phillips
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Rainfall Variability ◽  
Circulation Model ◽  
Internal Variability ◽  
Tropical Pacific ◽  
Atmospheric Variability ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
The Tropical Pacific

Abstract Atmospheric general circulation model experiments are conducted to quantify the contribution of internal oceanic variability in the form of tropical instability waves (TIWs) to interannual wind and rainfall variability in the tropical Pacific. It is found that in the tropical Pacific, along the equator, and near 25°N and 25°S, TIWs force a significant increase in wind and rainfall variability from interseasonal to interannual time scales. Because of the stochastic nature of TIWs, this means that climate models that do not take them into account will underestimate the strength and number of extreme events and may overestimate forecast capability.

scholarly journals A Tropospheric Emission Spectrometer HDO/H<sub>2</sub>O retrieval simulator for climate models

2012 ◽  
Vol 12 (6) ◽  
pp. 13827-13880
Author(s):  
R. D. Field ◽  
C. Risi ◽  
G. A. Schmidt ◽  
J. Worden ◽  
A. Voulgarakis ◽  
...  
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Satellite Measurement ◽  
Climate Simulations ◽  
Accurate Comparison ◽  
Free Running ◽  
The Tropics ◽  
Short Time

Abstract. Retrievals of the isotopic composition of water vapor from the Aura Tropospheric Emission Spectrometer (TES) have unique value in constraining moist processes in climate models. Accurate comparison between simulated and retrieved values requires that model profiles that would be poorly retrieved are excluded, and that an instrument operator be applied to the remaining profiles. Typically, this is done by sampling model output at satellite measurement points and using the quality flags and averaging kernels from individual retrievals at specific places and times. This approach is not reliable when the modeled meteorological conditions influencing retrieval sensitivity are different from those observed by the instrument at short time scales, which will be the case for free-running climate simulations. In this study, we describe an alternative, "categorical" approach to applying the instrument operator, implemented within the NASA GISS ModelE general circulation model. Retrieval quality and averaging kernel structure are predicted empirically from model conditions, rather than obtained from collocated satellite observations. This approach can be used for arbitrary model configurations, and requires no agreement between satellite-retrieved and modeled meteorology at short time scales. To test this approach, nudged simulations were conducted using both the retrieval-based and categorical operators. Cloud cover, surface temperature and free-tropospheric moisture content were the most important predictors of retrieval quality and averaging kernel structure. There was good agreement between the δD fields after applying the retrieval-based and more detailed categorical operators, with increases of up to 30‰ over the ocean and decreases of up to 40‰ over land relative to the raw model fields. The categorical operator performed better over the ocean than over land, and requires further refinement for use outside of the tropics. After applying the TES operator, ModelE had δD biases of −8‰ over ocean and −34‰ over land compared to TES δD, which were less than the biases using raw modeled δD fields.

Evaluation of the tail of the probability distribution of daily and sub-daily precipitation in CMIP6 models

2021 ◽  
pp. 1-61
Author(s):  
Jesse Norris ◽  
Alex Hall ◽  
J. David Neelin ◽  
Chad W. Thackeray ◽  
Di Chen
Keyword(s):  
General Circulation ◽  
Daily Precipitation ◽  
Precipitation Amount ◽  
Coupled Model ◽  
Lower Troposphere ◽  
General Circulation Models ◽  
Intercomparison Project ◽  
Cloud Tops ◽  
The Tropics ◽  
Fraction Models

AbstractDaily and sub-daily precipitation extremes in historical Coupled-Model-Intercomparison-Project-Phase-6 (CMIP6) simulations are evaluated against satellite-based observational estimates. Extremes are defined as the precipitation amount exceeded every x years, ranging from 0.01–10, encompassing the rarest events that are detectable in the observational record without noisy results. With increasing temporal resolution there is an increased discrepancy between models and observations: for daily extremes the multi-model median underestimates the highest percentiles by about a third, and for 3-hourly extremes by about 75% in the tropics. The novelty of the current study is that, to understand the model spread, we evaluate the 3-D structure of the atmosphere when extremes occur. In midlatitudes, where extremes are simulated predominantly explicitly, the intuitive relationship exists whereby higher-resolution models produce larger extremes (r=–0.49), via greater vertical velocity. In the tropics, the convective fraction (the fraction of precipitation simulated directly from the convective scheme) is more relevant. For models below 60% convective fraction, precipitation amount decreases with convective fraction (r=–0.63), but above 75% convective fraction, this relationship breaks down. In the lower-convective-fraction models, there is more moisture in the lower troposphere, closer to saturation. In the higher-convective-fraction models, there is deeper convection and higher cloud tops, which appears to be more physical. Thus, the low-convective models are mostly closer to the observations of extreme precipitation in the tropics, but likely for the wrong reasons. These inter-model differences in the environment in which extremes are simulated hold clues into how parameterizations could be modified in general circulation models to produce more credible 21st-Century projections.

Sensitivity of simulated oxygen isotopes in ice cores and speleothems to Last Glacial Maximum surface conditions

2021 ◽  
Author(s):  
André Paul ◽  
Alexandre Cauquoin ◽  
Stefan Mulitza ◽  
Thejna Tharammal ◽  
Martin Werner
Keyword(s):  
Last Glacial Maximum ◽  
General Circulation ◽  
Ice Cores ◽  
General Circulation Models ◽  
Glacial Maximum ◽  
Sea Surface ◽  
Surface Conditions ◽  
Last Glacial ◽  
The Impact ◽  
Mean Square Errors

&lt;p&gt;In simulations of the climate during the Last Glacial Maximum (LGM), we employ two different isotope-enabled atmospheric general circulation models (NCAR iCAM3 and MPI ECHAM6-wiso) and use simulated (by coupled climate models) as well as reconstructed (from a new global climatology of the ocean surface duing the LGM, GLOMAP) surface conditions.&lt;/p&gt;&lt;p&gt;The resulting atmospheric fields reflect the more pronounced structure and gradients in the reconstructions, for example, the precipitation is more depleted in oxygen-18 in the high latitudes and more enriched in low latitudes, especially in the tropical convective regions over the maritime continent in the equatorial Pacific and Indian Oceans and over the equatorial Atlantic Ocean. Furthermore, at the sites of ice cores and speleothems, the model-data fit improves in terms of the coefficients of determination and root-mean square errors.&lt;/p&gt;&lt;p&gt;In additional sensitivity experiments, we also use the climatologies by Annan and Hargreaves (2013) and Tierney et al. (2020) and consider the impact of changes in reconstructed sea-ice extent and the global-mean sea-surface temperature.&lt;/p&gt;&lt;p&gt;Our findings imply that the correct simulation or reconstruction of patterns and gradients in sea-surface conditions are crucial for a successful comparison to oxygen-isotope data from ice cores and speleothems.&lt;/p&gt;

scholarly journals A Simplistic Approach for Assessing Hydroclimatic Vulnerability of Lakes and Reservoirs with Regulated Superficial Outflow

Hydrology ◽  
2019 ◽  
Vol 6 (3) ◽  
pp. 61 ◽  
Author(s):  
Kleoniki Demertzi ◽  
Dimitris Papadimos ◽  
Vassilis Aschonitis ◽  
Dimitris Papamichail
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
Drainage Basin ◽  
Management Strategies ◽  
General Circulation Models ◽  
Climatic Conditions ◽  
Modified Model ◽  
Natural Lakes ◽  
The Future ◽  
The Impact

This study proposes a simplistic model for assessing the hydroclimatic vulnerability of lakes/reservoirs (LRs) that preserve their steady-state conditions based on regulated superficial discharge (Qd) out of the LR drainage basin. The model is a modification of the Bracht-Flyr et al. method that was initially proposed for natural lakes in closed basins with no superficial discharge outside the basin (Qd = 0) and under water-limited environmental conditions {mean annual ratio of potential/reference evapotranspiration (ETo) versus rainfall (P) greater than 1}. In the proposed modified approach, an additional Qd function is included. The modified model is applied using as a case study the Oreastiada Lake, which is located inside the Kastoria basin in Greece. Six years of observed data of P, ETo, Qd, and lake topography were used to calibrate the modified model based on the current conditions. The calibrated model was also used to assess the future lake conditions based on the future climatic projections (mean conditions of 2061-2080) derived by 19 general circulation models (GCMs) for three cases of climate change (three cases of Representative Concentration Pathways: RCP2.6, RCP4.5 and RCP8.5). The modified method can be used as a diagnostic tool in water-limited environments for analyzing the superficial discharge changes of LRs under different climatic conditions and to support the design of new management strategies for mitigating the impact of climate change on (a) flooding conditions, (b) hydroelectric production, (c) irrigation/industrial/domestic use and (d) minimum ecological flows to downstream rivers.

scholarly journals Weights for general circulation models from CMIP3/CMIP5 in a statistical downscaling framework and the impact on future Mediterranean precipitation

2019 ◽  
Vol 39 (8) ◽  
pp. 3639-3654 ◽  
Author(s):  
Irena Kaspar‐Ott ◽  
Elke Hertig ◽  
Severin Kaspar ◽  
Felix Pollinger ◽  
Christoph Ring ◽  
...  
Keyword(s):  
Statistical Downscaling ◽  
General Circulation ◽  
General Circulation Models ◽  
The Impact
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