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  • American Meteorological Society
  • 2025-2025
  • 2020-2022  (3,408)
  • 1950-1954  (897)
  • 1940-1944  (1,861)
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  • 1
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    An Analysis of 2016–18 Tornadoes and National Weather Service Tornado Warnings across the Contiguous United States (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-12-01
    Description: Previous work has considered tornado occurrence with respect to radar data, both WSR-88D and mobile research radars, and a few studies have examined techniques to potentially improve tornado warning performance. To date, though, there has been little work focusing on systematic, large-sample evaluation of National Weather Service (NWS) tornado warnings with respect to radar-observable quantities and the near-storm environment. In this work, three full years (2016–18) of NWS tornado warnings across the contiguous United States were examined, in conjunction with supporting data in the few minutes preceding warning issuance, or tornado formation in the case of missed events. The investigation herein examines WSR-88D and Storm Prediction Center (SPC) mesoanalysis data associated with these tornado warnings with comparisons made to the current Warning Decision Training Division (WDTD) guidance. Combining low-level rotational velocity and the significant tornado parameter (STP), as used in prior work, shows promise as a means to estimate tornado warning performance, as well as relative changes in performance as criteria thresholds vary. For example, low-level rotational velocity peaking in excess of 30 kt (15 m s−1), in a near-storm environment, which is not prohibitive for tornadoes (STP 〉 0), results in an increased probability of detection and reduced false alarms compared to observed NWS tornado warning metrics. Tornado warning false alarms can also be reduced through limiting warnings with weak (1 n mi; 1 n mi = 1.852 km) circulations in a poor (STP = 0) environment, careful elimination of velocity data artifacts like sidelobe contamination, and through greater scrutiny of human-based tornado reports in otherwise questionable scenarios.
    Print ISSN: 0882-8156
    Electronic ISSN: 1520-0434
    Topics: Geography , Physics
    Published by American Meteorological Society
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  • 2
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    A Global Perspective of Tropical Cyclone Precipitation in Reanalyses (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-11-01
    Description: This study compares the spread in climatological tropical cyclone (TC) precipitation across eight different reanalysis datasets: NCEP-CFSR, ERA-20C, ERA-40, ERA5, ERA-Interim, JRA-55, MERRA-2, and NOAA-20C. TC precipitation is assigned using manual tracking via a fixed 500-km radius from each TC center. The reanalyses capture similar general spatial patterns of TC precipitation and TC precipitation fraction, defined as the fraction of annual precipitation assigned to TCs, and the spread in TC precipitation is larger than the spread in total precipitation across reanalyses. The spread in TC precipitation relative to the inter-reanalysis mean TC precipitation, or relative spread, is larger in the east Pacific than in the west Pacific. Partitioned by reanalysis intensity, the largest relative spread across reanalyses in TC precipitation is from high-intensity TCs. In comparison with satellite observations, reanalyses show lower climatological mean annual TC precipitation over most areas. A comparison of area-averaged precipitation rate in TCs composited over reanalysis intensity shows the spread across reanalyses is larger for higher intensity TCs. Testing the sensitivity of TC precipitation assignment to tracking method shows that climatological mean annual TC precipitation is systematically larger when assigned via manual tracking versus objective tracking. However, this tendency is minimized when TC precipitation is normalized by TC density. Overall, TC precipitation in reanalyses is affected by not only horizontal output resolution or any TC preprocessing, but also data assimilation and parameterization schemes. The results indicate that improvements in the representation of TCs and their precipitation in reanalyses are needed to improve overall precipitation.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 3
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    Understanding the Basin Asymmetry in Surface Response to Sudden Stratospheric Warmings from an Ocean–Atmosphere Coupled Perspective (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-11-01
    Description: The canonical tropospheric response to a weakening of the stratospheric vortex—an equatorward shift of the eddy-driven jet—is mostly limited to the North Atlantic following sudden stratospheric warmings (SSWs). A coherent change in the Pacific eddy-driven jet is notably absent. Why is this so? Using daily reanalysis data, we show that air–sea interactions over the North Pacific are responsible for the basin-asymmetric response to SSWs. Prior to the onset of some SSWs, their tropospheric precursors produce a dipolar SST pattern in the North Pacific, which then persists as the stratospheric polar vortex breaks down following the onset of the SSW. By reinforcing the lower-tropospheric baroclinicity, the dipolar SST pattern helps sustain the generation of baroclinic eddies, strengthening the near-surface Pacific eddy-driven jet and maintaining its near-climatological-mean state. This prevents the jet from being perturbed by the downward influence of the stratospheric anomalies. As a result, these SSWs exhibit a highly basin-asymmetric surface response with only the Atlantic eddy-driven jet shifted equatorward. For SSWs occurring without the atmospheric precursors in the North Pacific troposphere, the dipolar SST pattern is absent due to the lack of the atmospheric forcing. In the absence of the dipolar SST pattern and the resultant eddy–mean flow feedbacks, these SSWs exhibit a basin-symmetric surface response with both the Atlantic and the Pacific eddy-driven jets shifted equatorward. Our results provide an ocean–atmosphere coupled perspective on stratosphere–troposphere interaction following SSW events and have potential for improving subseasonal to seasonal forecasts for surface weather and climate.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 4
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    Mechanisms of Regional Winter Sea-Ice Variability in a Warming Arctic (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-11-01
    Description: The Arctic winter sea ice cover is in retreat overlaid by large internal variability. Changes to sea ice are driven by exchange of heat, momentum, and freshwater within and between the ocean and the atmosphere. Using a combination of observations and output from the Community Earth System Model Large Ensemble, we analyze and contrast present and future drivers of the regional winter sea ice cover. Consistent with observations and previous studies, we find that for the recent decades ocean heat transport though the Barents Sea and Bering Strait is a major source of sea ice variability in the Atlantic and Pacific sectors of the Arctic, respectively. Future projections show a gradually expanding footprint of Pacific and Atlantic inflows highlighting the importance of future Atlantification and Pacification of the Arctic Ocean. While the dominant hemispheric modes of winter atmospheric circulation are only weakly connected to the sea ice, we find distinct local atmospheric circulation patterns associated with present and future regional sea ice variability in the Atlantic and Pacific sectors, consistent with heat and moisture transport from lower latitudes. Even if the total freshwater input from rivers is projected to increase substantially, its influence on simulated sea ice is small in the context of internal variability.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 5
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    Future Projection of Extreme Precipitation Indices over the Indochina Peninsula and South China in CMIP6 Models (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-11-01
    Description: A future projection of four extreme precipitation indices over the Indochina Peninsula and South China (INCSC) region with reference to the period 1958–2014 is conducted through the application of a multimodel ensemble approach and a rank-based weighting method. The weight of each model from phase 6 of the Coupled Model Intercomparison Project (CMIP6) is calculated depending on its historical simulation skill. Then, the weighted and unweighted ensembles are used for future projections. The results show that all four extreme precipitation indices are expected to increase over the INCSC region, both in the middle (2041–60) and at the end (2081–2100) of the twenty-first century, under three Shared Socioeconomic Pathway (SSP) scenarios. The increases in total extreme precipitation (R95p), extreme precipitation days (R95d), and the fraction of total rainfall from events exceeding the extreme precipitation threshold (R95pT) in the Indochina Peninsula are more significant than those in South China. The occurrence of extreme rainfall events may become more frequent in the future over the INCSC region, since the probability that R95pT increases is larger than 0.7 in the whole INCSC region. A comparison between the weighted and unweighted ensemble means shows that the uncertainty over South China is almost always reduced after applying the weighted scheme to future probabilistic projection, while the reductions in uncertainty over the Indochina Peninsula may depend on SSPs. The more extreme precipitation over the INCSC region in the future may be related to the larger water vapor supply and the more unstable local atmospheric stratification.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 6
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    Reanalyses and a High-Resolution Model Fail to Capture the “High Tail” of CAPE Distributions (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-11-01
    Description: Convective available potential energy (CAPE) is of strong interest in climate modeling because of its role in both severe weather and in model construction. Extreme levels of CAPE (〉2000 J kg−1) are associated with high-impact weather events, and CAPE is widely used in convective parameterizations to help determine the strength and timing of convection. However, to date few studies have systematically evaluated CAPE biases in models in a climatological context, and none have addressed bias in the high tail of CAPE distributions. This work compares CAPE distributions in ~200 000 summertime proximity soundings from four sources: the observational radiosonde network [Integrated Global Radiosonde Archive (IGRA)], 0.125° reanalyses (ERA-Interim and ERA5), and a 4-km convection-permitting regional WRF simulation driven by ERA-Interim. Both reanalyses and the WRF Model consistently show too-narrow distributions of CAPE, with the high tail (〉90th percentile) systematically biased low by up to 10% in surface-based CAPE and even more in alternate CAPE definitions. This “missing tail” corresponds to the most impacts-relevant conditions. CAPE bias in all datasets is driven by surface temperature and humidity: reanalyses and the WRF Model underpredict observed cases of extreme heat and moisture. These results suggest that reducing inaccuracies in land surface and boundary layer models is critical for accurately reproducing CAPE.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
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  • 7
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    Tracing the Origin of the South Asian Summer Monsoon Precipitation and Its Variability Using a Novel Lagrangian Framework (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-11-01
    Description: The water sources and their variability responsible for the South Asian summer monsoon precipitation were analyzed using Lagrangian atmospheric water-mass trajectories. The results indicated that evaporated waters from the central and south Indian Ocean are the major contributors to the South Asian summer monsoon rainfall, followed by the contribution from the local recycling (precipitated water that evapotranspirated from the South Asian landmass), the Arabian Sea, remote sources, and the Bay of Bengal. It was also found that although the direct contribution originating from the Bay of Bengal is small, it still provides a pathway for the atmospheric water that comes from other regions. This pathway is hence only crossing over the Bay of Bengal. The outcomes further revealed that the evaporated waters originating from the central and south Indian Ocean are responsible for the net precipitation over the coastal regions of the Ganges–Brahmaputra–Meghna Delta, northeast India, Myanmar, the foothills of the Himalayas, and central-east India. Evaporated waters from the Arabian Sea are mainly contributing to the rainfall over the western coast and west-central India. Summer monsoon precipitation due to the local recycling is primarily restricted to the Indo-Gangetic plain. No recycled precipitation was observed over the mountain chain along the west coast of India (Western Ghats). The month-to-month precipitation variation over South Asia was analyzed to be linked with the Somali low-level jet variability. The interannual variability of the South Asian summer monsoon precipitation was found to be mainly controlled by the atmospheric waters that were sourced and traveled from the central and south Indian Ocean.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
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  • 8
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    Convective couplings with equatorial Rossby waves and equatorial Kelvin waves. Part I: Coupled wave structures. (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-10-28
    Description: This study investigates precipitation amounts and apparent heat sources, which are coupled with equatorial Kelvin waves and equatorial Rossby waves, using TRMM PR level 2 data products. The synoptic structures of wave disturbances are also studied using the ERA5 reanalysis dataset. We define the wave phase of equatorial waves based on FFT filtered brightness temperature and conduct composite analyses. Rossby waves show a vertically upright structure and their upright vortices induce large amplitude column water vapor (CWV) anomalies. Precipitation activity is almost in phase with CWV, and thus is consistent with a moisture mode. Kelvin waves, on the other hand, indicate a nearly quadrature phase relationship between temperature and vertical velocity, like gravity wave structure. Specific humidity develops from near the surface to middle troposphere as the Kelvin wave progresses. A clear negative CWV anomaly also does not exist despite the existence of negative precipitation anomalies. Convective activity corresponds well with its tilting structure of moisture and modulates the phase relationship between temperature and vertical motion. For both wave cases, apparent heat sources can amplify available potential energy despite of the difference of coupling mechanisms of these two waves; precipitation is driven by CWV fluctuation for the Rossby wave case, and by buoyancy-based fluctuations for the Kelvin wave case. These can be an observational evidence of actual coupling processes that is comparable to previous idealized studies.
    Print ISSN: 0022-4928
    Electronic ISSN: 1520-0469
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 9
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    New Perspectives on Ensemble Sensitivity Analysis with Applications to a Climatology of Severe Convection (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-10-28
    Description: Ensemble sensitivity analysis (ESA) is a statistical technique applied within an ensemble to reveal the atmospheric flow features that relate to a chosen aspect of the flow. Given its ease of use (it is simply a linear regression between a chosen function of the forecast variables and the entire atmospheric state earlier or simultaneously in time), ensemble sensitivity has been the focus of several studies over roughly the last ten years. Such studies have primarily tried to understand the relevant dynamics and/or key precursors of high-impact weather events. Other applications of ESA have been more operationally oriented, including observation targeting within data assimilation systems and real-time adjustment techniques that attempt to utilize both sensitivity information and observations to improve forecasts.While ESA has gained popularity, its fundamental properties remain a substantially underutilized basis for realizing the technique’s full scientific potential. For example, the relationship between ensemble sensitivity and the pure dynamics of the system can teach us how to appropriately apply various sensitivity-based applications, and combining sensitivity with other ensemble properties such as spread can distinguish between a fluid dynamics problem and a predictability one. This work aims to present new perspectives on ensemble sensitivity, and clarify its fundamentals, with the hopes of making it a more accessible, attractive, and useful tool in the atmospheric sciences. These new perspectives are applied in part to a short climatology of severe convection forecasts to demonstrate the unique knowledge that can gained through broadened use of ESA.
    Print ISSN: 0003-0007
    Electronic ISSN: 1520-0477
    Topics: Geography , Physics
    Published by American Meteorological Society
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  • 10
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    Reconstructing Precipitation Events Using Co-located Soil Moisture Information (2021)
    American Meteorological Society
    Details
    Publication Date: 2021-10-28
    Description: Complete and accurate precipitation records are important for developing reliable flood warning systems, streamflow forecasts, rainfall-runoff estimates, and numerical land surface predictions. Existing methods for flagging missing precipitation events and filling gaps in the precipitation record typically rely on precipitation from neighboring stations. In this study, we investigated an alternative method for back-calculating precipitation events using changes in rootzone soil water storage. Our hypothesis was that using a different variable (i.e., soil moisture) from the same monitoring station will be more accurate in estimating hourly precipitation than using the same variable (i.e., precipitation) from the nearest neighboring station. Precipitation events were estimated from soil moisture as the sum of hourly changes in profile soil water storage. Hourly precipitation and soil moisture observations were obtained for a mesoscale network in the central U.S. Great Plains from May 2017 to December 2020. The proposed method based on soil moisture had a minimum detectable limit of 7.6 mm (95th percentile of undetected precipitation events) due to canopy and soil interception. The method was outperformed by the nearest neighbor (NN) interpolation method when neighboring stations were at distances of 10 km. Using changes in soil water storage resulted effective in flagging and reconstructing actual missing precipitation events caused by pluviometer malfunction, highlighting new opportunities for using readily available in situ soil moisture information for operational quality control in mesoscale environmental monitoring networks.
    Print ISSN: 1525-755X
    Electronic ISSN: 1525-7541
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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