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You searched for subject:(climate model biases). Showing records 1 – 3 of 3 total matches.

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University of New South Wales

1. Choudhury, Dipayan. CMIP5 Decadal Predictions: Implications for Australian Hydrology.

Degree: Faculty of Engineering, 2017, University of New South Wales

Effective prediction of regional climate, especially rainfall, at interannual to decadal timescales is of considerable importance to decision makers. To investigate predictions at these timescales, a new set of climate model experiments, called the ‘decadal’ experiments was set up as part of CMIP5. Simulation of rainfall in climate models, however, is often poor and the decadal experiments provide little predictability for rainfall. Previous work has demonstrated that SST has greater predictability and sea surface temperature (SST) has a strong influence on terrestrial rainfall. Thus, SST predictions can be used to derive rainfall ahead of time. Such Indo-Pacific SST-rainfall relationships are used operationally in the seasonal forecasting of Australian rainfall. On this basis, the thesis investigates the possibility of rainfall prediction over Australia at interannual timescales using outputs of SST from these decadal experiments.The prediction skills of nine SST indices that are relevant predictors of Australian rainfall are first quantified. It is found that most indices are not predictable beyond the first year. Two approaches for enhancing their predictability timescale are examined: 1) Investigating the effect of drift on predictability and identifying the drift correction method that leads to the best predictability 2) Identifying other indices that inherently have a higher predictability.The key findings around model drift include: (i) under sampling of initialisation years can lead to spurious estimates of drift and predictability limits over the tropical Pacific, (ii) prediction skill is enhanced with more complicated drift correction methods, and (iii) drift correcting individual models prior to multi-model averaging leads to clear improvements in skill.This thesis also examined in detail a newly identified Pacific-Atlantic transbasin climate mode, TBV, to be significantly related to Australian rainfall. We found that this mode showed predictability timescales that exceeded El Niño Southern Oscillation (ENSO) across multiple models. Most importantly, we showed the co-occurrence of TBV and ENSO to intensify the drying and wetting effects of ENSO over Australia.Using all this information, a simple rainfall prediction model is designed and applied over Australia. The results show that there is indeed merit in decadal predictions of SST for interannual rainfall prediction over Australia. Advisors/Committee Members: Sharma, Ashish, Civil & Environmental Engineering, Faculty of Engineering, UNSW, Sengupta, Alex, Climate Change Research Centre (CCRC), Faculty of Science, UNSW, Bellie, Sivakumar, Civil & Environmental Engineering, Faculty of Engineering, UNSW, Mehrotra, Rajeshwar, Civil & Environmental Engineering, Faculty of Engineering, UNSW.

Subjects/Keywords: Sea surface temperature; Decadal prediction; Australian rainfall; Climate model biases

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Choudhury, D. (2017). CMIP5 Decadal Predictions: Implications for Australian Hydrology. (Doctoral Dissertation). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/58583

Chicago Manual of Style (16th Edition):

Choudhury, Dipayan. “CMIP5 Decadal Predictions: Implications for Australian Hydrology.” 2017. Doctoral Dissertation, University of New South Wales. Accessed October 21, 2019. http://handle.unsw.edu.au/1959.4/58583.

MLA Handbook (7th Edition):

Choudhury, Dipayan. “CMIP5 Decadal Predictions: Implications for Australian Hydrology.” 2017. Web. 21 Oct 2019.

Vancouver:

Choudhury D. CMIP5 Decadal Predictions: Implications for Australian Hydrology. [Internet] [Doctoral dissertation]. University of New South Wales; 2017. [cited 2019 Oct 21]. Available from: http://handle.unsw.edu.au/1959.4/58583.

Council of Science Editors:

Choudhury D. CMIP5 Decadal Predictions: Implications for Australian Hydrology. [Doctoral Dissertation]. University of New South Wales; 2017. Available from: http://handle.unsw.edu.au/1959.4/58583


University of Miami

2. Simon, Steven. Variability of Midtropospheric Humidity and its Modulation of Convective Precipitation.

Degree: MS, Meteorology and Physical Oceanography (Marine), 2019, University of Miami

The spatiotemporal distribution of tropospheric moisture plays a significant role in modulating the global climate system and its associated variability on a multitude of scales. Along with its role in regulating tropospheric temperatures via various direct and indirect radiative effects, tropospheric water vapor and its phase changes in the Global Tropics provide large sources of latent heating and cooling, which in turn drive vertical and horizontal transport processes that drive convection and the underlying global hydrological cycle. Past hydrological studies, using both observational retrievals and model simulations, have investigated the contemporaneous link between sustained tropical deep convective rainfall and variations in tropospheric humidity and found that a near-universal nonlinear relationship exists between precipitation intensity and tropospheric moisture, such that precipitation intensity increases exponentially beyond a threshold in tropospheric column water vapor and tropical convection rapidly transitions towards a deep convective regime. While such studies have highlighted that this inflection point in convective tropical precipitation intensity is sensitive to variations in vertically integrated free tropospheric moisture, there is less certainty with regards to which specific layers of moisture within the vertical tropospheric column induce or condition the aforementioned transitions in tropical precipitation intensity. This uncertainty is further compounded and highlighted by biases associated with how modern state-of-the-art global climate models simulate precipitation intensity and frequency in the Global Tropics, i.e. a tendency to overestimate light precipitation frequency, but underestimate heavy precipitation frequency relative to what is depicted by observations.Nonetheless, recent work has found that midtropospheric moisture positively impacts vertical development within tropical convective systems by significantly diluting the effects of convective inhibition provided by dry air entrainment in the mid-levels of the troposphere via a plume buoyancy framework. Using a recently developed tropical midtropospheric relative humidity dataset derived from remotely-sensed high frequency microwave radiances, along with observational and global climate model (GCM)-based tropical datasets for column moisture, precipitation, temperature, and specific humidity, this study endeavored towards establishing a more comprehensive understanding of the role that midtropospheric moisture variability plays in modulating daily tropical precipitation intensity and influencing transitions amongst precipitation intensity regimes in the Global Tropics. In doing so, this study sought to not only investigate how our current understanding of the nonlinear relationship between tropical precipitation intensity and tropospheric moisture manifests as an independent or joint function and distribution of column water vapor (CWV) and midtropospheric relative humidity (MTH), but also to determine the degree to which… Advisors/Committee Members: Brian Soden, Amy Clement, Benjamin Kirtman, Jayantha Obeysekera.

Subjects/Keywords: Tropical Convective Precipitation; Midtropospheric Moisture; Precipitation Regime Transitions; Global Climate Model Biases; Remotely Sensed Precipitation and Water Vapor

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Simon, S. (2019). Variability of Midtropospheric Humidity and its Modulation of Convective Precipitation. (Thesis). University of Miami. Retrieved from https://scholarlyrepository.miami.edu/oa_theses/753

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Simon, Steven. “Variability of Midtropospheric Humidity and its Modulation of Convective Precipitation.” 2019. Thesis, University of Miami. Accessed October 21, 2019. https://scholarlyrepository.miami.edu/oa_theses/753.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Simon, Steven. “Variability of Midtropospheric Humidity and its Modulation of Convective Precipitation.” 2019. Web. 21 Oct 2019.

Vancouver:

Simon S. Variability of Midtropospheric Humidity and its Modulation of Convective Precipitation. [Internet] [Thesis]. University of Miami; 2019. [cited 2019 Oct 21]. Available from: https://scholarlyrepository.miami.edu/oa_theses/753.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Simon S. Variability of Midtropospheric Humidity and its Modulation of Convective Precipitation. [Thesis]. University of Miami; 2019. Available from: https://scholarlyrepository.miami.edu/oa_theses/753

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


University of Washington

3. Atlas, Rachel. In-situ Observations and Large Eddy Simulations of Southern Ocean Boundary Layer Clouds.

Degree: 2019, University of Washington

Southern Ocean boundary layer clouds affect global albedo and oceanic heat uptake. Most climate models and reanalyses underestimate cloudiness in the Southern Ocean, which biases seas surface temperatures and tropospheric winds, and likely influences the global atmospheric circulation and oceanic heat uptake. This robust and persistent model bias reveals gaps in our understanding of the physical controls on the formation and evolution of low clouds in the Southern Ocean, compared to more well-studied regions. The physics of Southern Ocean boundary layer clouds are uncertain due, in part, to a lack of in-situ observations in the region. Here, I use recent state-of-the-art measurements from the SOCRATES aircraft campaign and cloud resolving simulations, to investigate the influence of synoptic dynamics, boundary layer structure and microphysical properties on Southern Ocean boundary layer clouds. I developed a technique for simulating boundary layer clouds in the synoptically active Southern Ocean with a large eddy simulation (LES) and I set up five modelling case studies from SOCRATES observations. I find that the LES realistically represents diverse boundary layer structures but produces clouds with persistently low liquid water paths. CAM6 persistently underestimates droplet concentrations and cloud driven turbulence. Advisors/Committee Members: Bretherton, Christopher (advisor).

Subjects/Keywords: boundary layer structure; climate model biases; large eddy simulation; low clouds; mixed-phase microphysics; southern ocean; Atmospheric sciences; Climate change; Atmospheric sciences

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Atlas, R. (2019). In-situ Observations and Large Eddy Simulations of Southern Ocean Boundary Layer Clouds. (Thesis). University of Washington. Retrieved from http://hdl.handle.net/1773/44027

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Atlas, Rachel. “In-situ Observations and Large Eddy Simulations of Southern Ocean Boundary Layer Clouds.” 2019. Thesis, University of Washington. Accessed October 21, 2019. http://hdl.handle.net/1773/44027.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Atlas, Rachel. “In-situ Observations and Large Eddy Simulations of Southern Ocean Boundary Layer Clouds.” 2019. Web. 21 Oct 2019.

Vancouver:

Atlas R. In-situ Observations and Large Eddy Simulations of Southern Ocean Boundary Layer Clouds. [Internet] [Thesis]. University of Washington; 2019. [cited 2019 Oct 21]. Available from: http://hdl.handle.net/1773/44027.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Atlas R. In-situ Observations and Large Eddy Simulations of Southern Ocean Boundary Layer Clouds. [Thesis]. University of Washington; 2019. Available from: http://hdl.handle.net/1773/44027

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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