Oceanography The Official Magazine of
The Oceanography Society
Volume 32 Issue 02

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Volume 32, No. 2
Pages 58 - 65

High-Resolution Rain Maps from an X-band Marine Radar and Their Use in Understanding Ocean Freshening

Elizabeth J. Thompson William E. AsherAndrew T. JessupKyla Drushka
Article Abstract

Ship-based X-band radar observations of rain were collected with high spatial resolution during the 2016 and 2017 Salinity Processes in the Upper-ocean Regional Study 2 (SPURS-2) field experiments in the eastern tropical Pacific Ocean. These observations were collected with a repurposed marine radar that is not typically used for weather monitoring. The radar images captured during SPURS-2 show the spatial extent and variable intensity of rain at a horizontal resolution of 180 m within 30 km of the ship. When analyzed alongside collocated measurements of oceanic and atmospheric properties collected during SPURS-2, the radar-derived rain maps enable a clearer understanding of the impact of spatially and temporally varying freshwater fluxes on ocean salinity. Ocean surface freshening, measured by ship gauges, is found to be affected by local rain accumulation, and also by prior rain accumulation in surrounding locations that was measured by radar. In one example, the X-band marine radar measured rain directly ahead of the ship’s path. The ship then sampled a near-surface freshening signature within the time period expected based on the ship speed, ship heading, and rain area measured by the radar. ­


Thompson, E.J., W.E. Asher, A.T. Jessup, and K. Drushka. 2019. High-resolution rain maps from an X-band marine radar and their use in understanding ocean freshening. Oceanography 32(2):58–65, https://doi.org/10.5670/oceanog.2019.213.


Anderson, J.E., and S.C. Riser. 2014. Near-surface variability of temperature and salinity in the near-tropical ocean: Observations from profiling floats. Journal of Geophysical Research 119:7,433–7,448, https://doi.org/10.1002/2014JC010112.

Anderson, S.P., R.A. Weller, and R.B. Lukas. 1996. Surface buoyancy forcing and the mixed layer of the Western Pacific Warm Pool: Observations and 1D model results. Journal of Climate 9:3,056–3,085, https://doi.org/​10.1175/​1520-0442(1996)009​<3056:SBFATM>2.0.CO;2.

Asher, W.E., A.T. Jessup, R. Branch, and D. Clark. 2014. Observations of rain-induced near surface salinity anomalies. Journal of Geophysical Research 119(8):5,483–5,500, https://doi.org/​10.1002/2014JC009954.

Berger, J., J. Orcutt, S. Foley, and S. Bohlen. 2006. HiSeasNet: Oceanographic ships join the grid. Eos, Transactions American Geophysical Union 87(18):174, https://doi.org/​10.1029/2006EO180009.

Bringi, V.N., and V. Chandrasekar. 2001. Polarimetric Doppler Weather Radar: Principles and Applications. Cambridge University Press, 636 pp.

Chiu, L.S., A.T.C. Chang, and J. Janowiak. 1993. Comparison of monthly rain rates derived from gpi and ssm/i using probability distribution functions. Journal of Applied Meteorology 32(2):323–334, https://doi.org/10.1175/1520-0450(1993)032​<0323:COMRRD>2.0.CO;2.

Clayson, C.A., J.B. Edson, A. Paget, R. Graham, and B. Greenwood. 2019. Effects of rainfall on the atmosphere and the ocean during SPURS-2. Oceanography 32(2):86–97, https://doi.org/​10.5670/oceanog.2019.216.

Drushka, K., J. Sprintall, S.T. Gille, and S. Wijffels. 2012. In situ observations of Madden–Julian Oscillation mixed layer dynamics in the Indian and Western Pacific Oceans. Journal of Climate 25:2,306–2,328, https://doi.org/10.1175/JCLI-D-11-00203.1.

Drushka, K., W.E. Asher, B. Ward, and K. Walesby. 2016. Understanding the formation and evolution of rain-formed fresh lenses at the ocean surface. Journal of Geophysical Research 121:2,673–2,689, https://doi.org/10.1002/2015JC011527.

Drushka, K., W.E. Asher, A.T. Jessup, E. Thomson, S. Iyer, and D. Clark. 2019. Capturing fresh layers with the surface salinity profiler. Oceanography 32(2):76–85, https://doi.org/​10.5670/oceanog.2019.215.

Fairall, C.W., E.F. Bradley, J.S. Godfrey, G.A. Wick, J.B. Edson, and G.S. Young. 1996. Cool-skin and warm-layer effects on sea surface temperature. Journal of Geophysical Research 101:1,295–1,308, https://doi.org/10.1029/95JC03190.

Farrar, J.T., and A.J. Plueddemann. 2019. On the factors driving upper-ocean salinity variability at the western edge of the Eastern Pacific Fresh Pool. Oceanography 32(2):30–39, https://doi.org/​10.5670/oceanog.2019.209.

Grant, L.D., T.P. Lane, and S.C. van den Heever. 2018. The role of cold pools in tropical oceanic convective systems. Journal of the Atmospheric Sciences 75:2,615–2,634, https://doi.org/10.1175/JAS-D-17-0352.1.

Houze, R.A. 1997. Stratiform precipitation in regions of convection: A meteorological paradox? Bulletin of the American Meteorological Society 78(10):2,179–2,196, https://doi.org/10.1175/​1520-0477(1997)078​<2179:SPIROC>2.0.CO;2.

Hudlow, M.D. 1979. Mean rainfall patterns for the three phases of GATE. Journal of Applied Meteorology 18:1,656–1,669, https://doi.org/10.1175/1​520-0450(1979)018​<1656:MRPFTT>2.0.CO;2.

Johnson, R.H., T.M. Rickenbach, S.A. Rutledge, P.E. Ciesielski, and W.H. Schubert. 1999. Trimodal characteristics of tropical convection. Journal of Climate 12:2,397–2,418, https://doi.org/10.1175/1520-0442(1999)012​<2397:TCOTC>2.0.CO;2.

Johnson, R.H., P.E. Ciesielski, and J.A. Cotturone. 2001. Multiscale variability of the atmospheric mixed layer over the western Pacific warm pool. Journal of the Atmospheric Sciences 58:2,729–2,750, https://doi.org/10.1175/​1520-0469(2001)058​<2729:MVOTAM>2.0.CO;2.

Johnson, R.H., and P.E. Ciesielski. 2017. Multiscale variability of the atmospheric boundary layer during DYNAMO. Journal of the Atmospheric Sciences 74:4,003–4,021, https://doi.org/10.1175/JAS-D-17-0182.1.

Kawai, Y., and A. Wada. 2007. Diurnal sea surface temperature variation and its impact on the atmosphere and ocean: A review. Journal of Oceanography 63:721–744, https://doi.org/10.1007/s10872-007-0063-0.

Kummerow, C. 1998. Beamfilling errors in passive microwave rainfall retrievals. Journal of Applied Meteorology 37(4):356–370, https://doi.org/10.1175/1520-0450(1998)037<0356:BEIPMR>2.0.CO;2.

Kummerow, C., W. Barnes, T. Kozu, J. Shiue, and J. Simpson. 1998. The Tropical Rainfall Measuring Mission (TRMM) sensor package. Journal of Atmospheric and Oceanic Technology 15:809–817, https://doi.org/10.1175/1520-0426(1998)015​<0809:TTRMMT>2.0.CO;2.

Lee, P.H.Y., J.D. Barter, K.L. Beach, C.L. Hindman, B.M. Lake, H. Rungaldier, J.C. Shelton, A.B. Williams, R. Yee, and H.C. Yuen. 1995. X band microwave backscattering from ocean waves. Journal of Geophysical Research 100(C2):2,591–2,611, https://doi.org/10.1029/94JC02741.

Lukas, R., and E. Lindstrom.1991. The mixed layer of the Western Equatorial Pacific Ocean. Journal of Geophysical Research 96:3,343–3,357, https://doi.org/10.1029/90JC01951.

Nesbitt, S.W., R. Cifelli, and S.A. Rutledge. 2006. Storm morphology and rainfall characteristics of TRMM precipitation features. Monthly Weather Review 134(10):2,702–2,721, https://doi.org/10.1175/MWR3200.1.

Petersen, W.A., R.C. Cifelli, S.A. Rutledge, B.S. Ferrier, and B.F. Smull. 1999. Shipborne dual-​Doppler operations during TOGA COARE: Integrated observations of storm kinematics and electrification. Bulletin of the American Meteorological Society 80:81–98, https://doi.org/10.1175/1520-0477(1999)080<0081:SDDODT>2.0.CO;2.

Price, J.F. 1979. Observations of a rain-formed mixed layer. Journal of Physical Oceanography 9(3):643–649, https://doi.org/​10.1175/​1520-​0485​(1979)009​<0643:OOARFM>​2.0.CO;2.

Rutledge, S.A., V. Chandrasekar, B. Fuchs, J. George, F. Junyent, P. Kennedy, and B. Dolan. 2019. Deployment of the SEA-POL C-band polarimetric radar to SPURS-2. Oceanography 32(2):50–57, https://doi.org/10.5670/oceanog.2019.212.

Skofronick-Jackson, G., W.A. Petersen, W. Berg, C. Kidd, E.F. Stocker, D.B. Kirschbaum, R. Kakar, S.A. Braun, G.J. Huffman, T. Iguchi, and others. 2017. The Global Precipitation Measurement (GPM) Mission for science and society. Bulletin of the American Meteorological Society 98:1,679–1,695, https://doi.org/10.1175/BAMS-D-15-00306.1.

Soloviev, A., and R. Lukas. 2006: The Near-Surface Layer of the Ocean: Structure, Dynamics and Applications. Atmospheric and Oceanographic Sciences Library, vol. 24, Springer, Netherlands, 552 pp., https://doi.org/10.1007/978-94-007-7621-0.

Soloviev, A.V., S. Matt, and A. Fujimura. 2015. Three-dimensional dynamics of fresh​water lenses in the ocean’s near-surface layer. Oceanography 28(1):142–149, https://doi.org/​10.5670/oceanog.2015.14.

Sprintall, J., and M. Tomczak. 1992. Evidence of the barrier layer in the surface layer of the tropics. Journal of Geophysical Research 97:7,305–7,316, https://doi.org/10.1029/92JC00407.

Tan, J., W.A. Petersen, P. Kirstetter, and Y. Tian. 2017. Performance of IMERG as a function of spatiotemporal scale. Journal of Hydrometeorology 18:307–319, https://doi.org/​10.1175/JHM-D-16-0174.1.

Thompson, E.J., S.A. Rutledge, B. Dolan, and M. Thurai. 2015. Drop size distributions and radar observations of convective and stratiform rain over the equatorial Indian and west Pacific Oceans. Journal of the Atmospheric Sciences 72(11):4,091–4,125, https://doi.org/10.1175/JAS-D-14-0206.1.

Thompson, E.J., S.A. Rutledge, B. Dolan, M. Thurai, and V. Chandrasekar. 2018. Dual-polarization radar rainfall estimation over tropical oceans. Journal of Applied Meteorology and Climatology 57:755–775, https://doi.org/10.1175/JAMC-D-17-0160.1.

Thompson, E.J., J.N. Moum, C.W. Fairall, and S.A. Rutledge. 2019. Wind limits on rain layers and diurnal warm layers. Journal of Geophysical Research 124:897–924, https://doi.org/​10.1029/2018JC014130.

Torri, G., and Z. Kuang. 2016. A Lagrangian study of precipitation-driven downdrafts. Journal of the Atmospheric Sciences 73:839–854, https://doi.org/​10.1175/JAS-D-15-0222.1.

Trivej, P., and B. Stevens. 2010. The echo size distribution of precipitating shallow cumuli. Journal of the Atmospheric Sciences 67:788–804, https://doi.org/​10.1175/​2009JAS3178.1.

Viltard, N., C. Burlaud, and C.D. Kummerow. 2006. Rain retrieval from TMI brightness temperature measurements using a TRMM PR–based database. Journal of Applied Meteorology and Climatology 45:455–466, https://doi.org/10.1175/JAM2346.1.

Wilheit, T.T., A.T. Chang, and L.S. Chiu. 1991. Retrieval of monthly rainfall indices from microwave radiometric measurements using probability distribution functions. Journal of Atmospheric and Oceanic Technology 8(1):118–136, https://doi.org/10.1175/1520-0426(1991)008<0118:ROMRIF>2.0.CO;2.

Xu, W., and S.A. Rutledge. 2014. Convective characteristics of the Madden-Julian Oscillation over the Central Indian Ocean observed by shipborne radar during DYNAMO. Journal of the Atmospheric Sciences 71:2,859–2,877, https://doi.org/10.1175/JAS-D-13-0372.1.

Xu, W., and S.A. Rutledge. 2015. Morphology, intensity, and rainfall production of MJO convection: Observations from DYNAMO shipborne radar and TRMM. Journal of the Atmospheric Sciences 72:623–640, https://doi.org/10.1175/JAS-D-14-0130.1.

Wijesekera, H.W., C.A. Paulson, and A. Huyer. 1999. The effect of rainfall on the surface layer during a westerly wind burst in the western equatorial Pacific. Journal of Geophysical Research 29:612–632, https://doi.org/10.1175/1520-0485(1999)029​<0612:TEOROT>2.0.CO;2.

You, Y. 1995. Salinity variability and its role in the barrier-layer formation during TOGA-COARE. Journal of Physical Oceanography 25:2,778–2,807, https://doi.org/10.1175/1520-0485(1995)025​<2778:SVAIRI>2.0.CO;2.