Spatiotemporal variations in momentum flux spectra of convective gravity waves (CGWs) at the source level (cloud top), including nonlinear forcing effects, are examined based on calculations using an offline version of CGW parameterization and global reanalysis data for a period of 32 years (1979-2010). The cloud-top momentum flux (CTMF) is not solely proportional to the convective heating rate but is affected by the wave-filtering and resonance factor and background stability and temperature underlying the convection. Consequently, the primary peak of CTMF is in the winter hemisphere midlatitudes, associated with storm tracks, where a secondary peak of convective heating exists, whereas the secondary peak of CTMF appears in the summer hemisphere tropics and intertropical convergence zone (ITCZ), where the primary peak of convective heating exists. The magnitude of CTMF fluctuates largely with 1-yr and 1-day periods in major CTMF regions. At low latitudes and Pacific storm-track regions, a 6-month period is also significant, and the decadal cycle appears in the southern Andes. The equatorial eastern Pacific region exhibits a substantial interannual to decadal scale of variabilities. The correlation between convective heating and the CTMF is relatively lower in the equatorial region than in other regions. The CTMF in 10°N-10°S during the period of the pre-Concordiasi campaign approximately follows a lognormal distribution but with a slight underestimation in the tail of the probability density function. In Part II, the momentum flux and drag of CGW in the stratosphere will be examined.
Bibliographical noteFunding Information:
Acknowledgments. This work was funded by the Korea Meteorological Administration Research and Development Program under Grant KMIPA 2015-6160. The NCEP CFSR data were downloaded from the Research Data Archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory, Boulder, Colorado (available online at http://dx.doi.org/10.5065/D69K487J), and from the National Oceanic and Atmospheric Administration (NOAA) Operational Model Archive and Distribution System, National Climatic Data Center, Asheville, North Carolina (available online at http://nomads.ncdc. noaa.gov/modeldata/cmd_pgbh/). The authors thank the anonymous reviewers for many helpful comments and suggestions. We would also like to thank Dr. In-Sun Song and Dr. Hyun-Joo Choi for their helpful advice on this study.
© 2017AmericanMeteorological Society.
All Science Journal Classification (ASJC) codes
- Atmospheric Science