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• 1. [Article] Evaluation of Large‑Scale Meteorological Patterns Associated with Temperature Extremes in the NARCCAP Regional Climate Model Simulations

  Large-scale meteorological patterns (LSMPs) associated with temperature extremes are evaluated in a suite of regional climate model (RCM) simulations contributing to the North American Regional Climate ...

  Citation × Citation Citation Abstract Copy Title: Evaluation of Large‑Scale Meteorological Patterns Associated with Temperature Extremes in the NARCCAP Regional Climate Model Simulations Author: Loikith, Paul C., Waliser, Duane E., Lee, Huikyo, Neelin, J. David, Lintner, Benjamin, McGinnis, Seth, Mears, Linda, Kim, Jinwon Year: 2015 Large-scale meteorological patterns (LSMPs) associated with temperature extremes are evaluated in a suite of regional climate model (RCM) simulations contributing to the North American Regional Climate Change Assessment Program. LSMPs are characterized through composites of surface air temperature, sea level pressure, and 500 hPa geopotential height anomalies concurrent with extreme temperature days. Six of the seventeen RCM simulations are driven by boundary conditions from reanalysis while the other eleven are driven by one of four global climate models (GCMs). Four illustrative case studies are analyzed in detail. Model fidelity in LSMP spatial representation is high for cold winter extremes near Chicago. Winter warm extremes are captured by most RCMs in northern California, with some notable exceptions. Model fidelity is lower for cool summer days near Houston and extreme summer heat events in the Ohio Valley. Physical interpretation of these patterns and identification of wellsimulated cases, such as for Chicago, boosts confidence in the ability of these models to simulate days in the tails of the temperature distribution. Results appear consistent with the expectation that the ability of an RCM to reproduce a realistically shaped frequency distribution for temperature, especially at the tails, is related to its fidelity in simulating LMSPs. Each ensemble member is ranked for its ability to reproduce LSMPs associated with observed warm and cold extremes, identifying systematically high performing RCMs and the GCMs that provide superior boundary forcing. The methodology developed here provides a framework for identifying regions where further process-based evaluation would improve the understanding of simulation error and help guide future model improvement and downscaling efforts. Title: Evaluation of Large‑Scale Meteorological Patterns Associated with Temperature Extremes in the NARCCAP Regional Climate Model Simulations Author: Loikith, Paul C., Waliser, Duane E., Lee, Huikyo, Neelin, J. David, Lintner, Benjamin, McGinnis, Seth, Mears, Linda, Kim, Jinwon Year: 2015 Large-scale meteorological patterns (LSMPs) associated with temperature extremes are evaluated in a suite of regional climate model (RCM) simulations contributing to the North American Regional Climate Change Assessment Program. LSMPs are characterized through composites of surface air temperature, sea level pressure, and 500 hPa geopotential height anomalies concurrent with extreme temperature days. Six of the seventeen RCM simulations are driven by boundary conditions from reanalysis while the other eleven are driven by one of four global climate models (GCMs). Four illustrative case studies are analyzed in detail. Model fidelity in LSMP spatial representation is high for cold winter extremes near Chicago. Winter warm extremes are captured by most RCMs in northern California, with some notable exceptions. Model fidelity is lower for cool summer days near Houston and extreme summer heat events in the Ohio Valley. Physical interpretation of these patterns and identification of wellsimulated cases, such as for Chicago, boosts confidence in the ability of these models to simulate days in the tails of the temperature distribution. Results appear consistent with the expectation that the ability of an RCM to reproduce a realistically shaped frequency distribution for temperature, especially at the tails, is related to its fidelity in simulating LMSPs. Each ensemble member is ranked for its ability to reproduce LSMPs associated with observed warm and cold extremes, identifying systematically high performing RCMs and the GCMs that provide superior boundary forcing. The methodology developed here provides a framework for identifying regions where further process-based evaluation would improve the understanding of simulation error and help guide future model improvement and downscaling efforts. Close

• 2. [Article] Observational studies of stable nocturnal boundary layers: intermittent turbulence, sensible heat budgets and observational errors

  Atmospheric boundary layers become stably stratified at night over land when the surface becomes colder than the air layer above. In stable nocturnal boundary layers (SNBL), turbulence becomes weak and ...

  Citation × Citation Citation Abstract Copy Title: Observational studies of stable nocturnal boundary layers: intermittent turbulence, sensible heat budgets and observational errors Author: Nakamura, Reina Atmospheric boundary layers become stably stratified at night over land when the surface becomes colder than the air layer above. In stable nocturnal boundary layers (SNBL), turbulence becomes weak and intermittent, terrain-induced phenomena such as drainage currents or gravity-waves emerge and the surface heterogeneity is enhanced. Because of their complexity and insufficient observations, a comprehensive understanding of SNBLs is not yet achieved. In the first study of this dissertation, characteristics of intermittent turbulence in SNBLs are investigated with data collected from a network of towers. Toward this goal, turbulence kinetic energy budget, predictability and spatial extent of intermittent turbulence patches are examined. A series of analyses suggests intermittent turbulence evolves and decays as it is advected between two adjacent towers separated by 100 m or more. In the second study, systematic observational errors of air temperature due to radiative forcing and ambiguity of the standardized measurement height over nonuniform vegetation are quantified and contrasted. An empirical formula is developed for correcting the radiatively-induced error. Implications for the systematic errors in atmospheric boundary layer research, such as estimation of horizontal temperature advection, are discussed. In the third study, the structure of SNBLs is investigated in terms of the sensible heat budget. As opposed to previous assumptions, the nocturnal heat budget cannot be generally balanced by the storage, vertical heat flux divergence and vertical radiative flux divergence only. An error analysis suggests that instrumental and sampling errors are unable to explain the large imbalance, implying the significance of systematic advection of potential temperature and possibly the mesoscale heat flux divergence in the heat budget. Advection of intermittent turbulence and potential temperature has been found to be more significant in SNBLs than previously thought. Advection estimates can be challenging due to various observational errors as illustrated with an example of air temperature. Nonetheless, for better understanding of SNBLs, observational strategies or methodologies need to be improved for directly evaluating advection. Title: Observational studies of stable nocturnal boundary layers: intermittent turbulence, sensible heat budgets and observational errors Author: Nakamura, Reina Atmospheric boundary layers become stably stratified at night over land when the surface becomes colder than the air layer above. In stable nocturnal boundary layers (SNBL), turbulence becomes weak and intermittent, terrain-induced phenomena such as drainage currents or gravity-waves emerge and the surface heterogeneity is enhanced. Because of their complexity and insufficient observations, a comprehensive understanding of SNBLs is not yet achieved. In the first study of this dissertation, characteristics of intermittent turbulence in SNBLs are investigated with data collected from a network of towers. Toward this goal, turbulence kinetic energy budget, predictability and spatial extent of intermittent turbulence patches are examined. A series of analyses suggests intermittent turbulence evolves and decays as it is advected between two adjacent towers separated by 100 m or more. In the second study, systematic observational errors of air temperature due to radiative forcing and ambiguity of the standardized measurement height over nonuniform vegetation are quantified and contrasted. An empirical formula is developed for correcting the radiatively-induced error. Implications for the systematic errors in atmospheric boundary layer research, such as estimation of horizontal temperature advection, are discussed. In the third study, the structure of SNBLs is investigated in terms of the sensible heat budget. As opposed to previous assumptions, the nocturnal heat budget cannot be generally balanced by the storage, vertical heat flux divergence and vertical radiative flux divergence only. An error analysis suggests that instrumental and sampling errors are unable to explain the large imbalance, implying the significance of systematic advection of potential temperature and possibly the mesoscale heat flux divergence in the heat budget. Advection of intermittent turbulence and potential temperature has been found to be more significant in SNBLs than previously thought. Advection estimates can be challenging due to various observational errors as illustrated with an example of air temperature. Nonetheless, for better understanding of SNBLs, observational strategies or methodologies need to be improved for directly evaluating advection. Close

• 3. [Article] Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica

  A 1-D ice cover model was developed to predict and constrain drivers of long-term ice thick-ness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface ra-diative ...

  Citation × Citation Citation Abstract Copy Title: Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica Author: Obryk, Maciej K., Doran, Peter T., Hicks, Jared A., McKay, Christopher P., Priscu, John Charles Year: 2016 A 1-D ice cover model was developed to predict and constrain drivers of long-term ice thick-ness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface ra-diative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 a (between 1996 and 2012) of ice thickness changes for the west lobe of Lake Bonney (average ice thickness = 3.53 m) and Lake Fryxell (average ice thickness = 4.22 m). Long-term ice thick-ness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or fa-cilitate ice thickness change depending on the predominant climatic trend (cooling or warming). As such, shallow (columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation. Title: Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica Author: Obryk, Maciej K., Doran, Peter T., Hicks, Jared A., McKay, Christopher P., Priscu, John Charles Year: 2016 A 1-D ice cover model was developed to predict and constrain drivers of long-term ice thick-ness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface ra-diative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 a (between 1996 and 2012) of ice thickness changes for the west lobe of Lake Bonney (average ice thickness = 3.53 m) and Lake Fryxell (average ice thickness = 4.22 m). Long-term ice thick-ness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or fa-cilitate ice thickness change depending on the predominant climatic trend (cooling or warming). As such, shallow (columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation. Close