• Bonner, W. D., 1968: Climatology of the low level jet. Mon. Wea. Rev., 96, 833850, https://doi.org/10.1175/1520-0493(1968)096<0833:COTLLJ>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bosilovich, M. G., and Coauthors, 2015: MERRA-2: Initial evaluation of the climate. NASA Tech. Memo. NASA/TM-2015-104606/Vol. 43, 145 pp., https://gmao.gsfc.nasa.gov/pubs/docs/Bosilovich803.pdf.

  • Budikova, D., T. W. Ford, and T. J. Ballinger, 2019: United States heat wave frequency and Arctic ocean marginal sea ice variability. J. Geophys. Res. Atmos., 124, 62476264, https://doi.org/10.1029/2018JD029365.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bumbaco, K. A., K. D. Dello, and N. A. Bond, 2013: History of Pacific Northwest heat waves: Synoptic patterns and trends. J. Appl. Meteor. Climatol., 52, 16181631, https://doi.org/10.1175/JAMC-D-12-094.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Burrows, D. A., C. R. Ferguson, and M. A. Campbell, 2019: An objective classification and analysis of upper-level coupling to the Great Plains low-level jet over the twentieth century. J. Climate, 32, 71277152, https://doi.org/10.1175/JCLI-D-18-0891.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chang, F.-C., and J. M. Wallace, 1987: Meteorological conditions during heat waves and droughts in the United States Great Plains. Mon. Wea. Rev., 115, 12531269, https://doi.org/10.1175/1520-0493(1987)115<1253:MCDHWA>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chen, R., and R. Lu, 2014: Dry tropical nights and wet extreme heat in Beijing: Atypical configurations between high temperature and humidity. Mon. Wea. Rev., 142, 17921802, https://doi.org/10.1175/MWR-D-13-00289.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chen, Y., and Y. Li, 2017: An inter-comparison of three heat wave types in China during 1961–2010: Observed basic features and linear trends. Sci. Rep., 7, 45619, https://doi.org/10.1038/srep45619.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chen, Y., and P. Zhai, 2017: Revisiting summertime hot extremes in China during 1961–2015: Overlooked compound extremes and significant changes. Geophys. Res. Lett., 44, 50965103, https://doi.org/10.1002/2016GL072281.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Cheng, L., M. Hoerling, Z. Liu, and J. Eischeid, 2019: Physical understanding of human-induced changes in U.S. hot droughts using equilibrium climate simulations. J. Climate, 32, 44314443, https://doi.org/10.1175/JCLI-D-18-0611.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Cloutier-Bisbee, S. R., A. Raghavendra, and S. M. Milrad, 2019: Heat waves in Florida: Climatology, trends, and related precipitation events. J. Appl. Meteor. Climatol., 58, 447466, https://doi.org/10.1175/JAMC-D-18-0165.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Dousset, B., F. Gourmelon, K. Laaidi, A. Zeghnoun, E. Giraudet, P. Bretin, E. Mauri, and S. Vandentorren, 2011: Satellite monitoring of summer heat waves in the Paris metropolitan area. Int. J. Climatol., 31, 313323, https://doi.org/10.1002/joc.2222.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Draper, C. S., R. H. Reichle, and R. D. Koster, 2018: Assessment of MERRA-2 land surface energy flux estimates. J. Climate, 31, 671691, https://doi.org/10.1175/JCLI-D-17-0121.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Fischer, E. M., S. I. Seneviratne, P. L. Vidale, D. Lüthi, and C. Schär, 2007: Soil moisture–atmosphere interactions during the 2003 European summer heat wave. J. Climate, 20, 50815099, https://doi.org/10.1175/JCLI4288.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ford, T. W., and J. T. Schoof, 2017: Characterizing extreme and oppressive heat waves in Illinois. J. Geophys. Res. Atmos., 122, 682698, https://doi.org/10.1002/2016JD025721.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Freychet, N., S. Tett, J. Wang, and G. Hegerl, 2017: Summer heat waves over eastern China: Dynamical processes and trend attribution. Environ. Res. Lett., 12, 024015, https://doi.org/10.1088/1748-9326/aa5ba3.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Gelaro, R., and Coauthors, 2017: The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). J. Climate, 30, 54195454, https://doi.org/10.1175/JCLI-D-16-0758.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Gershunov, A., D. R. Cayan, and S. F. Iacobellis, 2009: The great 2006 heat wave over California and Nevada: Signal of an increasing trend. J. Climate, 22, 61816203, https://doi.org/10.1175/2009JCLI2465.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Grotjahn, R., and Coauthors, 2016: North American extreme temperature events and related large scale meteorological patterns: A review of statistical methods, dynamics, modeling and trends. Climate Dyn., 46, 11511184, https://doi.org/10.1007/s00382-015-2638-6.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hajat, S., R. S. Kovats, R. W. Atkinson, and A. Haines, 2002: Impact of hot temperatures on death in London: A time series approach. J. Epidemiol. Community Health, 56, 367372, https://doi.org/10.1136/jech.56.5.367.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Helfand, H. M., and S. D. Schubert, 1995: Climatology of the simulated Great Plains low-level jet and its contribution to the continental moisture budget of the United States. J. Climate, 8, 784806, https://doi.org/10.1175/1520-0442(1995)008<0784:COTSGP>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hong, J.-S., S.-W. Yeh, and K.-H. Seo, 2018: Diagnosing physical mechanisms leading to pure heat waves versus pure tropical nights over the Korean Peninsula. J. Geophys. Res. Atmos., 123, 71497160, https://doi.org/10.1029/2018JD028360.

    • Search Google Scholar
    • Export Citation
  • Hu, L., J. Luo, G. Huang, and M. C. Wheeler, 2019: Synoptic features responsible for heat waves in central Africa, a region with strong multi-decadal trend. J. Climate, 32, 79517970, https://doi.org/10.1175/JCLI-D-18-0807.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kalkstein, L. S., 1991: A new approach to evaluate the impact of climate on human mortality. Environ. Health Perspect., 96, 145150, https://doi.org/10.1289/ehp.9196145.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kalkstein, L. S., and R. E. Davis, 1989: Weather and human mortality: An evaluation of demographic and interregional responses in the United States. Ann. Assoc. Amer. Geogr., 79, 4464, https://doi.org/10.1111/j.1467-8306.1989.tb00249.x.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kornhuber, K., S. Osprey, D. Coumou, S. Petri, V. Petoukhov, S. Rahmstorf, and L. Gray, 2019: Extreme weather events in early summer 2018 connected by a recurrent hemispheric wave-7 pattern. Environ. Res. Lett., 14, 054002, https://doi.org/10.1088/1748-9326/ab13bf.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Koster, R. D., and Coauthors, 2006a: GLACE: The Global Land-Atmosphere Coupling Experiment. Part I: Overview. J. Hydrometeor., 7, 590610, https://doi.org/10.1175/JHM510.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Koster, R. D., B. M. Fekete, G. J. Huffman, and P. W. Stackhouse, 2006b: Revisiting a hydrological analysis framework with International Satellite Land Surface Climatology Project Initiative 2 rainfall, net radiation, and runoff fields. J. Geophys. Res., 111, D22S05, https://doi.org/10.1029/2006JD007182.

    • Search Google Scholar
    • Export Citation
  • Koster, R. D., S. D. Schubert, and M. J. Suarez, 2009: Analyzing the concurrence of meteorological droughts and warm periods, with implications for the determination of evaporative regime. J. Climate, 22, 33313341, https://doi.org/10.1175/2008JCLI2718.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lau, N.-C., and M. J. Nath, 2012: A model study of heat waves over North America: Meteorological aspects and projections for the twenty-first century. J. Climate, 25, 47614784, https://doi.org/10.1175/JCLI-D-11-00575.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lehmann, J., and D. Coumou, 2015: The influence of mid-latitude storm tracks on hot, cold, dry and wet extremes. Sci. Rep., 5, 17491, https://doi.org/10.1038/srep17491.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Li, W., T. Zou, L. Li, Y. Deng, V. T. Sun, Q. Zhang, J. B. Layton, and S. Setoguchi, 2019: Impacts of the North Atlantic subtropical high on interannual variation of summertime heat stress over the conterminous United States. Climate Dyn., 53, 33453359, https://doi.org/10.1007/s00382-019-04708-1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Loikith, P. C., and A. J. Broccoli, 2012: Characteristics of observed atmospheric circulation patterns associated with temperature extremes over North America. J. Climate, 25, 72667281, https://doi.org/10.1175/JCLI-D-11-00709.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lopez, H., R. West, S. Dong, G. Goni, B. Kirtman, S.-K. Lee, and R. Atlas, 2018: Early emergence of anthropogenically forced heat waves in the western United States and Great Lakes. Nat. Climate Change, 8, 414420, https://doi.org/10.1038/s41558-018-0116-y.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lopez, H., S.-K. Lee, S. Dong, G. Goni, B. Kirtman, R. Atlas, and A. Kumar, 2019: East Asian monsoon as a modulator of U.S. Great Plains heat waves. J. Geophys. Res. Atmos., 124, 63426358, https://doi.org/10.1029/2018JD030151.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lyon, B., and A. G. Barnston, 2017: Diverse characteristics of U.S. summer heat waves. J. Climate, 30, 78277845, https://doi.org/10.1175/JCLI-D-17-0098.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Meehl, G., and C. Tebaldi, 2004: More intense, more frequent, and longer lasting heat waves in the 21st century. Science, 305, 994997, https://doi.org/10.1126/science.1098704.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Meehl, G., J. M. Arblaster, and G. Branstator, 2012: Mechanisms contributing to the warming hole and the consequent U.S. east–west differential of heat extremes. J. Climate, 25, 63946408, https://doi.org/10.1175/JCLI-D-11-00655.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Miralles, D. G., A. J. Teuling, C. C. van Heerwaarden, and J. Vila-Guerau de Arellano, 2014: Mega-heatwave temperatures due to combined soil desiccation and atmospheric heat accumulation. Nat. Geosci., 7, 345349, https://doi.org/10.1038/ngeo2141.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Namias, J., 1982: Anatomy of Great Plains protracted heat waves (especially the 1980 U.S. summer drought). Mon. Wea. Rev., 110, 824838, https://doi.org/10.1175/1520-0493(1982)110<0824:AOGPPH>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Oswald, E. M., 2018: An analysis of the prevalence of heat waves in the United States between 1948 and 2015. J. Appl. Meteor. Climatol., 57, 15351549, https://doi.org/10.1175/JAMC-D-17-0274.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Oswald, E. M., and R. B. Rood, 2014: A trend analysis of the 1930–2010 extreme heat events in the continental United States. J. Appl. Meteor. Climatol., 53, 565582, https://doi.org/10.1175/JAMC-D-13-071.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Perkins, S. E., 2015: A review on the scientific understanding of heatwaves—Their measurement, driving mechanisms, and changes at the global scale. Atmos. Res., 164165, 242267, https://doi.org/10.1016/j.atmosres.2015.05.014.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Perkins, S. E., and L. V. Alexander, 2013: On the measurement of heat waves. J. Climate, 26, 45004517, https://doi.org/10.1175/JCLI-D-12-00383.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Perkins, S. E., L. V. Alexander, and J. R. Nairn, 2012: Increasing frequency, intensity and duration of observed global heatwaves and warm spells. Geophys. Res. Lett., 39, L20714, https://doi.org/10.1029/2012GL053361.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Reichle, R. H., Q. Liu, R. D. Koster, C. S. Draper, S. P. P. Mahanama, and G. S. Partyka, 2017a: Land surface precipitation in MERRA-2. J. Climate, 30, 16431664, https://doi.org/10.1175/JCLI-D-16-0570.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Reichle, R. H., C. S. Draper, Q. Liu, M. Girotto, S. P. P. Mahanama, R. D. Koster, and G. J. M. De Lannoy, 2017b: Assessment of MERRA-2 land surface hydrology estimates. J. Climate, 30, 29372960, https://doi.org/10.1175/JCLI-D-16-0720.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Rennie, J., J. E. Bell, K. E. Kunkel, S. Herring, H. Cullen, and A. M. Abadi, 2019: Development of a submonthly temperature product to monitor near-real-time climate conditions and assess long-term heat events in the United States. J. Appl. Meteor. Climatol., 58, 26532674, https://doi.org/10.1175/JAMC-D-19-0076.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Rienecker, M. M., and Coauthors, 2011: MERRA: NASA’s Modern-Era retrospective analysis for research and applications. J. Climate, 24, 36243648, https://doi.org/10.1175/JCLI-D-11-00015.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Robinson, P. J., 2001: On the definition of a heat wave. J. Appl. Meteor., 40, 762775, https://doi.org/10.1175/1520-0450(2001)040<0762:OTDOAH>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Röthlisberger, M., L. Frossard, L. F. Bosart, D. Keyser, and O. Martius, 2019: Recurrent synoptic-scale Rossby wave patterns and their effect on the persistence of cold and hot spells. J. Climate, 32, 32073226, https://doi.org/10.1175/JCLI-D-18-0664.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ruprich-Robert, Y., T. Delworth, R. Msadek, F. Castruccio, S. Yeager, and G. Danabasoglu, 2018: Impacts of the Atlantic multidecadal variability on North American summer climate and heat waves. J. Climate, 31, 36793700, https://doi.org/10.1175/JCLI-D-17-0270.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Russo, S., J. Sillmann, and A. Sterl, 2017: Humid heat waves at different warming levels. Sci. Rep., 7, 7477, https://doi.org/10.1038/s41598-017-07536-7.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schoof, J. T., T. W. Ford, and S. C. Pryor, 2017: Recent changes in U.S. regional heat wave characteristics in observations and reanalyses. J. Appl. Meteor. Climatol., 56, 26212636, https://doi.org/10.1175/JAMC-D-16-0393.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schubert, S. D., H. M. Helfand, C.-Y. Wu, and W. Min, 1998: Subseasonal variations in warm-season moisture transport and precipitation over the central and eastern United States. J. Climate, 11, 25302555, https://doi.org/10.1175/1520-0442(1998)011<2530:SVIWSM>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schubert, S. D., H. Wang, and M. Suarez, 2011: Warm season subseasonal variability and climate extremes in the Northern Hemisphere: The role of stationary Rossby waves. J. Climate, 24, 47734792, https://doi.org/10.1175/JCLI-D-10-05035.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schubert, S. D., H. Wang, R. D. Koster, and M. J. Suarez, 2014: Northern Eurasian heat waves and droughts. J. Climate, 27, 31693207, https://doi.org/10.1175/JCLI-D-13-00360.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Shafiei Shiva, J., D. G. Chandler, and K. E. Kunkel, 2019: Localized changes in heat wave properties across the United States. Earth’s Future, 7, 300319, https://doi.org/10.1029/2018EF001085.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Smith, T. T., B. F. Zaitchik, and J. M. Gohlke, 2013: Heat waves in the United States: Definitions, patterns and trends. Climatic Change, 118, 811825, https://doi.org/10.1007/s10584-012-0659-2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Su, Q., and B. Dong, 2019: Recent decadal changes in heat waves over China: Drivers and mechanisms. J. Climate, 32, 42154234, https://doi.org/10.1175/JCLI-D-18-0479.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Teng, H., G. Branstator, H. Wang, G. A. Meehl, and W. M. Washington, 2013: Probability of US heat waves affected by a subseasonal planetary wave pattern. Nat. Geosci., 6, 10561061, https://doi.org/10.1038/ngeo1988.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Tuttle, J. D., and C. A. Davis, 2006: Corridors of warm season precipitation in the central United States. Mon. Wea. Rev., 134, 22972317, https://doi.org/10.1175/MWR3188.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Uccellini, L. W., and D. R. Johnson, 1979: The coupling of upper and lower tropospheric jet streaks and implications for the development of severe convective storms. Mon. Wea. Rev., 107, 682703, https://doi.org/10.1175/1520-0493(1979)107<0682:TCOUAL>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wang, A., and X. Zeng, 2013: Development of global hourly 0.5° land surface air temperature datasets. J. Climate, 26, 76767691, https://doi.org/10.1175/JCLI-D-12-00682.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wang, J., Y. Chen, S. F. B. Tett, Z. Yan, P. Zhai, J. Feng, and J. Xia, 2020: Anthropogenically-driven increases in the risks of summertime compound hot extremes. Nat. Commun., 11, 529, https://doi.org/10.1038/s41467-019-14233-8.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Weaver, S. J., and S. Nigam, 2008: Variability of the Great Plains low-level jet: Large-scale circulation context and hydroclimate impacts. J. Climate, 21, 15321551, https://doi.org/10.1175/2007JCLI1586.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wu, Z., H. Lin, J. Li, Z. Jiang, and T. Ma, 2012: Heat-wave frequency variability over North America: Two distinct leading modes. J. Geophys. Res., 117, D02102, https://doi.org/10.1029/2011JD016908.

    • Search Google Scholar
    • Export Citation
  • Wuebbles, D. J., D. W. Fahey, K. A. Hibbard, D. J. Dokken, B. C. Stewart, and T. K. Maycock, Eds., 2017: Climate Science Special Report: Fourth National Climate Assessment. U.S. Global Change Research Program, Vol. I, 470 pp., https://doi.org/10.7930/J0J964J6.

    • Crossref
    • Export Citation
  • Yang, Z., F. Dominguez, and X. Zeng, 2019: Large and local-scale features associated with heat waves in the United States in reanalysis products and the NARCCAP model ensemble. Climate Dyn., 52, 18831901, https://doi.org/10.1007/s00382-018-4414-x.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zhang, X., G. Hegerl, F. W. Zwiers, and J. Kenyon, 2005: Avoiding inhomogeneity in percentile-based indices of temperature extremes. J. Climate, 18, 16411651, https://doi.org/10.1175/JCLI3366.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
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Mechanisms Associated with Daytime and Nighttime Heat Waves over the Contiguous United States

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  • 1 Universities Space Research Association, Columbia, Maryland
  • 2 Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, Maryland
  • 3 Science Systems and Applications, Inc., Lanham, Maryland
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Abstract

Heat waves are extreme climate events that have the potential to cause immense stress on human health, agriculture, and energy systems, so understanding the processes leading to their onset is crucial. There is no single accepted definition for heat waves, but they are generally described as a sustained amount of time over which temperature exceeds a local threshold. Multiple different temperature variables are potentially relevant, because high values of both daily maximum and minimum temperatures can be detrimental to human health. In this study, we focus explicitly on the different mechanisms associated with summertime heat waves manifested during daytime hours versus nighttime hours over the contiguous United States. Heat waves are examined using the National Aeronautics and Space Administration Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). Over 1980–2018, the increase in the number of heat-wave days per summer was generally stronger for nighttime heat-wave days than for daytime heat-wave days, with localized regions of significant positive trends. Processes linked with daytime and nighttime heat waves are identified through composite analysis of precipitation, soil moisture, clouds, humidity, and fluxes of heat and moisture. Daytime heat waves are associated with dry conditions, reduced cloud cover, and increased sensible heating. Mechanisms leading to nighttime heat waves differ regionally across the United States, but they are typically associated with increased clouds, humidity, and/or low-level temperature advection. In the midwestern United States, enhanced moisture is transported from the Gulf of Mexico during nighttime heat waves.

© 2020 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

This article is included in the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) special collection.

Corresponding author: Natalie P. Thomas, natalie.p.thomas@nasa.gov

Abstract

Heat waves are extreme climate events that have the potential to cause immense stress on human health, agriculture, and energy systems, so understanding the processes leading to their onset is crucial. There is no single accepted definition for heat waves, but they are generally described as a sustained amount of time over which temperature exceeds a local threshold. Multiple different temperature variables are potentially relevant, because high values of both daily maximum and minimum temperatures can be detrimental to human health. In this study, we focus explicitly on the different mechanisms associated with summertime heat waves manifested during daytime hours versus nighttime hours over the contiguous United States. Heat waves are examined using the National Aeronautics and Space Administration Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). Over 1980–2018, the increase in the number of heat-wave days per summer was generally stronger for nighttime heat-wave days than for daytime heat-wave days, with localized regions of significant positive trends. Processes linked with daytime and nighttime heat waves are identified through composite analysis of precipitation, soil moisture, clouds, humidity, and fluxes of heat and moisture. Daytime heat waves are associated with dry conditions, reduced cloud cover, and increased sensible heating. Mechanisms leading to nighttime heat waves differ regionally across the United States, but they are typically associated with increased clouds, humidity, and/or low-level temperature advection. In the midwestern United States, enhanced moisture is transported from the Gulf of Mexico during nighttime heat waves.

© 2020 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

This article is included in the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) special collection.

Corresponding author: Natalie P. Thomas, natalie.p.thomas@nasa.gov
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