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  • American Meteorological Society  (38)
  • 1
    Online Resource
    Online Resource
    Increasing the Depth of a Land Surface Model. Part II: Temperature Sensitivity to Improved Subsurface Thermodynamics and Associated Permafrost Response
    American Meteorological Society ; 2021
    In:  Journal of Hydrometeorology Vol. 22, No. 12 ( 2021-12), p. 3231-3254
    Details
    In: Journal of Hydrometeorology, American Meteorological Society, Vol. 22, No. 12 ( 2021-12), p. 3231-3254
    Abstract: The impact of various modifications of the JSBACH land surface model to represent soil temperature and cold-region hydro-thermodynamic processes in climate projections of the twenty-first century is examined. We explore the sensitivity of JSBACH to changes in the soil thermodynamics, energy balance and storage, and the effect of including freezing and thawing processes. The changes involve 1) the net effect of an improved soil physical representation and 2) the sensitivity of our results to changed soil parameter values and their contribution to the simulation of soil temperatures and soil moisture, both aspects being presented in the frame of an increased bottom boundary depth from 9.83 to 1418.84 m. The implementation of water phase changes and supercooled water in the ground creates a coupling between the soil thermal and hydrological regimes through latent heat exchange. Momentous effects on subsurface temperature of up to ±3 K, together with soil drying in the high northern latitudes, can be found at regional scales when applying improved hydro-thermodynamic soil physics. The sensitivity of the model to different soil parameter datasets is relatively low but shows important implications for the root zone soil moisture content. The evolution of permafrost under preindustrial forcing conditions emerges in simulated trajectories of stable states that differ by 4–6 × 10 6 km 2 and shows large differences in the spatial extent of 10 5 –10 6 km 2 by 2100, depending on the model configuration.
    Type of Medium: Online Resource
    ISSN: 1525-755X , 1525-7541
    URL: Article
    DOI: 10.1175/JHM-D-21-0023.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2021
    detail.hit.zdb_id: 2042176-X
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  • 2
    Online Resource
    Online Resource
    Modulation of Marine Low Clouds Associated with the Tropical Intraseasonal Variability over the Eastern Pacific
    American Meteorological Society ; 2014
    In:  Journal of Climate Vol. 27, No. 14 ( 2014-07-15), p. 5560-5574
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 27, No. 14 ( 2014-07-15), p. 5560-5574
    Abstract: Owing to its profound influences on global energy balance, accurate representation of low cloud variability in climate models is an urgent need for future climate projection. In the present study, marine low cloud variability on intraseasonal time scales is characterized, with a particular focus over the Pacific basin during boreal summer and its association with the dominant mode of tropical intraseasonal variability (TISV) over the eastern Pacific (EPAC) intertropical convergence zone (ITCZ). Analyses indicate that, when anomalous TISV convection is enhanced over the elongated EPAC ITCZ, reduction of low cloud fraction (LCF) is evident over a vast area of the central North Pacific. Subsequently, when the enhanced TISV convection migrates to the northern part of the EPAC warm pool, a “comma shaped” pattern of reduced LCF prevails over the subtropical North Pacific, along with a pronounced reduction of LCF present over the southeast Pacific (SEPAC). Further analyses indicate that surface latent heat fluxes and boundary heights induced by anomalous low-level circulation through temperature advection and changes of total wind speed, as well as midlevel vertical velocity associated with the EPAC TISV, could be the most prominent factors in regulating the intraseasonal variability of LCF over the North Pacific. For the SEPAC, temperature anomalies at the top of the boundary inversion layer between 850 and 800 hPa play a critical role in the local LCF intraseasonal variations. Results presented in this study provide not only improved understanding of variability of marine low clouds and the underlying physics, but also a prominent benchmark in constraining and evaluating the representation of low clouds in climate models.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-13-00569.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 3
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    Online Resource
    Improved Madden–Julian Oscillations with Improved Physics: The Impact of Modified Convection Parameterizations
    American Meteorological Society ; 2012
    In:  Journal of Climate Vol. 25, No. 4 ( 2012-02-15), p. 1116-1136
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 25, No. 4 ( 2012-02-15), p. 1116-1136
    Abstract: Two modifications are made to the deep convection parameterization in the NCAR Community Climate System Model, version 3 (CCSM3): a dilute plume approximation and an implementation of the convective momentum transport (CMT). These changes lead to significant improvement in the simulated Madden–Julian oscillations (MJOs). With the dilute plume approximation, temperature and convective heating perturbations become more positively correlated. Consequently, more available potential energy is generated and the intraseasonal variability (ISV) becomes stronger. The organization of ISV is also improved, which is manifest in coherent structures between different MJO phases and an improved simulation of the eastward propagation of MJOs with a reasonable eastward speed. The improved propagation can be attributed to a better simulation of the low-level zonal winds due to the inclusion of CMT. The authors posit that the large-scale zonal winds are akin to a selective conveyor belt that facilitates the organization of ISVs into highly coherent structures, which are important features of observed MJOs. The conclusions are supported by two supplementary experiments, which include the dilute plume approximation and CMT separately.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/2011JCLI4059.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2012
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 4
    Online Resource
    Online Resource
    Profiles of Wind Speed Variances within Nocturnal Low-Level Jets Observed with a Sodar
    American Meteorological Society ; 2013
    In:  Journal of Atmospheric and Oceanic Technology Vol. 30, No. 9 ( 2013-09-01), p. 1970-1977
    Details
    In: Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 30, No. 9 ( 2013-09-01), p. 1970-1977
    Abstract: Continuous sodar measurements of wind profiles have been carried out at the Zvenigorod Scientific Station of the Obukhov Institute of Atmospheric Physics since 2008. The station is located in a slightly inhomogeneous rural area about 45 km west of Moscow, Russia. The data were used to determine the parameters of wind and turbulence within low-level jets in the stable atmospheric boundary layer (ABL). Along with the mean velocity profiles, the profiles of variances of wind speed components from the sodar and the profiles of temperature from a microwave radiometer have been used to quantify turbulence and thermal stratification. Data from two sonic anemometers were used to get the near-surface parameters. The typical standard deviation of the vertical wind component σw within the low-level jet is about 5% of the maximum wind speed in the jet. No noticeable vertical variation of σw across the jets was detected in several earlier sodar campaigns, and it was not found in the present study. An increase in horizontal variances was detected in zones of substantial wind shear, which agrees with earlier published lidar data. Quasi-periodic structures in the sodar return signal, which appear in sodar echograms as braid-shaped patterns, were found to emerge preferably when a substantial increase of wind shear occurs at the top of the stable ABL. The braid patterns in the sodar echograms were not accompanied by any noticeable increase of observed σw, which disagrees with earlier data and indicates that such patterns may originate from various phenomena.
    Type of Medium: Online Resource
    ISSN: 0739-0572 , 1520-0426
    URL: Article
    DOI: 10.1175/JTECH-D-12-00265.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2013
    detail.hit.zdb_id: 2021720-1
    detail.hit.zdb_id: 48441-6
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  • 5
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    Online Resource
    The Physics of Drought in the U.S. Central Great Plains
    American Meteorological Society ; 2016
    In:  Journal of Climate Vol. 29, No. 18 ( 2016-09-15), p. 6783-6804
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 29, No. 18 ( 2016-09-15), p. 6783-6804
    Abstract: The semiarid U.S. Great Plains is prone to severe droughts having major consequences for agricultural production, livestock health, and river navigation. The recent 2012 event was accompanied by record deficits in precipitation and high temperatures during the May–August growing season. Here the physics of Great Plains drought are explored by addressing how meteorological drivers induce soil moisture deficits during the growing season. Land surface model (LSM) simulations driven by daily observed meteorological forcing from 1950 to 2013 compare favorably with satellite-derived terrestrial water anomalies and reproduce key features found in the U.S. Drought Monitor. Results from simulations by two LSMs reveal that precipitation was directly responsible for between 72% and 80% of the soil moisture depletion during 2012, and likewise has accounted for the majority of Great Plains soil moisture variability since 1950. Energy balance considerations indicate that a large fraction of the growing season temperature variability is itself driven by precipitation, pointing toward an even larger net contribution of precipitation to soil moisture variability. To assess robustness across a larger sample of drought events, daily meteorological output from 1050 years of climate simulations, representative of conditions in 1979–2013, are used to drive two LSMs. Growing season droughts, and low soil moisture conditions especially, are confirmed to result principally from rainfall deficits. Antecedent meteorological and soil moisture conditions are shown to affect growing season soil moisture, but their effects are secondary to forcing by contemporaneous rainfall deficits. This understanding of the physics of growing season droughts is used to comment on plausible Great Plains soil moisture changes in a warmer world.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-15-0697.1
    DOI: 10.1175/JCLI-D-15-0697.s1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2016
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 6
    Online Resource
    Online Resource
    Modular, Flexible, Low-Cost Microstructure Measurements: The Epsilometer
    American Meteorological Society ; 2021
    In:  Journal of Atmospheric and Oceanic Technology Vol. 38, No. 3 ( 2021-03), p. 657-668
    Details
    In: Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 38, No. 3 ( 2021-03), p. 657-668
    Abstract: The Epsilometer (“epsi”) is a small (7 cm diameter × 30 cm long), low-power (0.15 W), and extremely modular microstructure package measuring thermal and kinetic energy dissipation rates, χ and ε . Both the shear probes and FP07 temperature sensors are fabricated in house following techniques developed by Michael Gregg at the Applied Physics Laboratory/University of Washington (APL/UW). Sampling eight channels (two shear, two temperature, three-axis accelerometer, and a spare for future sensors) at 24 bit precision and 325 Hz, the system can be deployed in standalone mode (battery power and recording to microSD cards) for deployment on autonomous vehicles, wave powered profilers, or it can be used with dropping body termed the “epsi-fish” for profiling from boats, autonomous surface craft or ships with electric fishing reels or other simple winches. The epsi-fish can also be used in real-time mode with the Scripps “fast CTD” winch for fully streaming, altimeter-equipped, line-powered, rapid-repeating, near-bottom shipboard profiles to 2200 m. Because this winch has a 25 ft (~7.6 m) boom deployable outboard from the ship, contamination by ship wake is reduced one to two orders of magnitude in the upper 10–15 m. The noise floor of ε profiles from the epsi-fish is ~10 −10 W kg −1 . This paper describes the fabrication, electronics, and characteristics of the system, and documents its performance compared to its predecessor, the APL/UW Modular Microstructure Profiler (MMP).
    Type of Medium: Online Resource
    ISSN: 0739-0572 , 1520-0426
    URL: Article
    DOI: 10.1175/JTECH-D-20-0116.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2021
    detail.hit.zdb_id: 2021720-1
    detail.hit.zdb_id: 48441-6
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  • 7
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    Online Resource
    Ocean Chlorophyll-Induced Heating Feedbacks on ENSO in a Coupled Ocean Physics–Biology Model Forced by Prescribed Wind Anomalies
    American Meteorological Society ; 2018
    In:  Journal of Climate Vol. 31, No. 5 ( 2018-03), p. 1811-1832
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 31, No. 5 ( 2018-03), p. 1811-1832
    Abstract: Ocean biology components affect the vertical redistribution of incoming solar radiation in the upper ocean of the tropical Pacific and can significantly modulate El Niño–Southern Oscillation (ENSO). The biophysical interactions in the region were represented by coupling an ocean biology model with an ocean general circulation model (OGCM); the coupled ocean physics–biology model is then forced by prescribed wind anomalies during 1980–2007. Two ocean-only experiments were performed with different representations of chlorophyll (Chl). In an interannual Chl run (referred to as Chl inter ), Chl was interannually varying, which was interactively calculated from the ocean biology model to explicitly represent its heating feedback on ocean thermodynamics. The structure and relationship of the related heating terms were examined to understand the Chl-induced feedback effects and the processes involved. The portion of solar radiation penetrating the bottom of the mixed layer ( Q pen ) was significantly affected by interannual Chl anomalies in the western-central equatorial Pacific. In a climatological run (Chl clim ), the Chl concentration was prescribed to be its seasonally varying climatology derived from the Chl inter run. Compared with the Chl clim run, interannual variability in the Chl inter run tended to be reduced. The sea surface temperature (SST) differences between the two runs exhibited an asymmetric bioeffect: they were stronger during La Niña events but relatively weaker during El Niño events. The signs of the SST differences between the two runs indicated a close relationship with Chl: a cooling effect was associated with a low Chl concentration during El Niño events, and a strong warming effect was associated with a high Chl concentration during La Niña events.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-17-0505.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2018
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 8
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    Future Projections of Extreme Ocean Wave Climates and the Relation to Tropical Cyclones: Ensemble Experiments of MRI-AGCM3.2H*
    American Meteorological Society ; 2015
    In:  Journal of Climate Vol. 28, No. 24 ( 2015-12-15), p. 9838-9856
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 28, No. 24 ( 2015-12-15), p. 9838-9856
    Abstract: Future projections of extreme ocean surface wave climates were carried out with single-model ensemble experiments of the atmospheric global climate model MRI-AGCM3.2H. The ensemble experiments of MRI-AGCM3.2H consist of four future sea surface temperature (SST) ensembles and three perturbed physics (PP) ensembles. This study showed that future changes in extreme wave heights strongly depend on the global climate model (GCM) performance to simulate tropical cyclones (TCs), indicating a need to acknowledge that results in a study that employs a low-performance model are not able to account for extreme waves associated with TCs (TC waves). The spatial distribution of future changes in non-TC extreme wave heights on the global scale was similar to that for mean wave heights; namely, wave heights increase over the middle-to-high latitudes in the Southern Ocean and central North Pacific and decrease over midlatitudes and the North Atlantic, although the magnitude of future changes for extreme wave heights is greater than for mean wave heights. The variance of future changes mainly depends on differences in physics among PP ensemble experiments rather than differences in SST ensembles. The 10-yr return wave heights of TC waves over the western North Pacific showed either an increase or a decrease of 30% for different regions, maximally. The spatial distribution of future changes in TC waves can be explained by an eastward shift of TC tracks.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-14-00711.1
    DOI: 10.1175/JCLI-D-14-00711.s1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2015
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 9
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    Online Resource
    Propagation of Thermohaline Anomalies and Their Predictive Potential along the Atlantic Water Pathway
    American Meteorological Society ; 2022
    In:  Journal of Climate Vol. 35, No. 7 ( 2022-04-01), p. 2111-2131
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 35, No. 7 ( 2022-04-01), p. 2111-2131
    Abstract: We assess to what extent seven state-of-the-art dynamical prediction systems can retrospectively predict winter sea surface temperature (SST) in the subpolar North Atlantic and the Nordic seas in the period 1970–2005. We focus on the region where warm water flows poleward (i.e., the Atlantic water pathway to the Arctic) and on interannual-to-decadal time scales. Observational studies demonstrate predictability several years in advance in this region, but we find that SST skill is low with significant skill only at a lead time of 1–2 years. To better understand why the prediction systems have predictive skill or lack thereof, we assess the skill of the systems to reproduce a spatiotemporal SST pattern based on observations. The physical mechanism underlying this pattern is a propagation of oceanic anomalies from low to high latitudes along the major currents, the North Atlantic Current and the Norwegian Atlantic Current. We find that the prediction systems have difficulties in reproducing this pattern. To identify whether the misrepresentation is due to incorrect model physics, we assess the respective uninitialized historical simulations. These simulations also tend to misrepresent the spatiotemporal SST pattern, indicating that the physical mechanism is not properly simulated. However, the representation of the pattern is slightly degraded in the predictions compared to historical runs, which could be a result of initialization shocks and forecast drift effects. Ways to enhance predictions could include improved initialization and better simulation of poleward circulation of anomalies. This might require model resolutions in which flow over complex bathymetry and the physics of mesoscale ocean eddies and their interactions with the atmosphere are resolved. Significance Statement In this study, we find that dynamical prediction systems and their respective climate models struggle to realistically represent ocean surface temperature variability in the eastern subpolar North Atlantic and Nordic seas on interannual-to-decadal time scales. In previous studies, ocean advection is proposed as a key mechanism in propagating temperature anomalies along the Atlantic water pathway toward the Arctic Ocean. Our analysis suggests that the predicted temperature anomalies are not properly circulated to the north; this is a result of model errors that seems to be exacerbated by the effect of initialization shocks and forecast drift. Better climate predictions in the study region will thus require improving the initialization step, as well as enhancing process representation in the climate models.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-20-1007.1
    DOI: 10.1175/JCLI-D-20-1007.s1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2022
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 10
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    Online Resource
    An Investigation of the Connections among Convection, Clouds, and Climate Sensitivity in a Global Climate Model
    American Meteorological Society ; 2014
    In:  Journal of Climate Vol. 27, No. 5 ( 2014-03-01), p. 1845-1862
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 27, No. 5 ( 2014-03-01), p. 1845-1862
    Abstract: This study explores connections between process-level modeling of convection and global climate model (GCM) simulated clouds and cloud feedback to global warming through a set of perturbed-physics and perturbed sea surface temperature experiments. A bulk diagnostic approach is constructed, and a set of variables is derived and demonstrated to be useful in understanding the simulated relationship. In particular, a novel bulk quantity, the convective precipitation efficiency or equivalently the convective detrainment efficiency, is proposed as a simple measure of the aggregated properties of parameterized convection important to the GCM simulated clouds. As the convective precipitation efficiency increases in the perturbed-physics experiments, both liquid and ice water path decrease, with low and middle cloud fractions diminishing at a faster rate than high cloud fractions. This asymmetry results in a large sensitivity of top-of-atmosphere net cloud radiative forcing to changes in convective precipitation efficiency in this limited set of models. For global warming experiments, intermodel variations in the response of cloud condensate, low cloud fraction, and total cloud radiative forcing are well explained by model variations in response to total precipitation (or detrainment) efficiency. Despite significant variability, all of the perturbed-physics models produce a sizable increase in precipitation efficiency to warming. A substantial fraction of the increase is due to its convective component, which depends on the parameterization of cumulus mixing and convective microphysical processes. The increase in convective precipitation efficiency and associated change in convective cloud height distribution owing to warming explains the increased cloud feedback and climate sensitivity in recently developed Geophysical Fluid Dynamics Laboratory GCMs. The results imply that a cumulus scheme using fractional removal of condensate for precipitation and inverse calculation of the entrainment rate tends to produce a lower climate sensitivity than a scheme using threshold removal for precipitation and the entrainment rate formulated inversely dependent on convective depth.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-13-00145.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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