Abstract
A significant declining trend in rainfall over the Congo basin has been observed over the past three decades. Since the Madden–Julian oscillation (MJO) is a major forcing mechanism for tropical convection and rainfall, the interannual variability and trend in rainfall over the Congo may be partly attributable to variability or changes in the MJO. This study explores the long-term (1979–2018) relationship between the active MJO diagnosed by the real-time multivariate (RMM) MJO phase index data and observed rainfall and cloud data over the Congo during October–March. Since the MJO may significantly enhance rainfall during the wet phases or suppress rainfall during the dry phases, the crux of this paper includes how trends in MJO activity may impact the overall observed precipitation trend over the Congo. The relationship between MJO activity and rainfall over the Congo was documented using statistical techniques and composite analysis. A new, yet simple approach was developed to partition seasonal rainfall depending on the MJO phase (i.e., wet, dry, inactive, and other). Results show a significant correlation between the number of wet and dry MJO days, and rainfall enhancement and suppression over the Congo. While there exists considerable interannual variability in MJO activity and rainfall over the Congo, there is a significant increase in the number of dry MJO days (3.47 days decade−1) which tends to intensify the large-scale drying trend over the Congo during October–March. The increasing trend in the number of dry MJO days is likely enhancing the net drying trend by 13.6% over the Congo.
Similar content being viewed by others
References
Adames AF, Wallace JM, Monteiro JM (2016) Seasonality of the structure and propagation characteristics of the MJO. J Atmos Sci 73:3511–3526
Alsdorf D et al (2016) Opportunities for hydrologic research in the Congo Basin. Rev Geophys 54:378–409
Barnes HC, Zuluaga MD, Houze RA (2015) Latent heating characteristics of the MJO computed from TRMM observations. J Geophys Res 120:1322–1334
Berhane F, Zaitchik B (2014) Modulation of daily precipitation over East Africa by the Madden–Julian Oscillation. J Climate 27:6016–6034
Chen D, Dai A (2019) Precipitation characteristics in the Community Atmosphere Model and their dependence on model physics and resolution. J Adv Model Earth Syst 11:2352–2374
Corfidi SF, Merritt JH, Fritsch JM (1996) Predicting the movement of mesoscale convective complexes. Weather Forecast 11:41–46
Creese A, Washington R, Jones R (2019) Climate change in the Congo Basin: processes related to wetting in the December–February dry season. Climate Dyn 53:3583–3602
Dai A (2006) Precipitation characteristics in eighteen coupled climate models. J Climate 19:4605–4630
Dee DP, Uppala SM, Simmons AJ et al (2011) The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Q J R Meteorol Soc 137:553–597
Dyer ELE, Jones DBA, Nusbaumer J, Li H, Collins O, Vettoretti G, Noone D (2017) Congo Basin precipitation: assessing seasonality, regional interactions, and sources of moisture. J Geophys Res Atmos 122:6882–6898
Gottschalck J, Wheeler M, Weickmann K, Vitart F, Savage N et al (2010) A framework for assessing operational Madden–Julian oscillation forecasts: a CLIVAR MJO working group project. Bull Am Meteorol Soc 91:1247–1258
Hamada A, Takayabu YN, Liu C, Zipser EJ (2015) Weak linkage between the heaviest rainfall and tallest storms. Nat Commun 6:6213
Held IM, Soden BJ (2006) Robust responses of the hydrological cycle to global warming. J Climate 19:5686–5699
Hill CM, Lin Y-L (2003) Initiation of a mesoscale convective complex over the Ethiopian Highlands preceding the genesis of Hurricane Alberto (2000). Geophys Res Lett 30:1232
Hirsch RM, Slack JR, Smith RA (1982) Techniques of trend analysis for monthly water quality data. Water Resour Res 18:107–121
Holton JR, Hakim GJ (2013) An introduction to dynamic meteorology. Elsevier, Amsterdam
Hua W, Zhou L, Chen H, Nicholson SE, Raghavendra A, Jiang Y (2016) Possible causes of the Central Equatorial African long-term drought. Environ Res Lett 11:124002
Hua W, Zhou L, Chen H, Nicholson SE, Jiang Y, Raghavendra A (2018) Understanding the Central Equatorial African long-term drought using AMIP-type simulations. Climate Dyn 50:1115–1128
Hua W, Zhou L, Nicholson SE, Chen H, Qin M (2019) Assessing reanalysis data for understanding rainfall climatology and variability over Central Equatorial Africa. Climate Dyn 53:651–669
Hung M, Lin J, Wang W, Kim D, Shinoda T, Weaver S (2013) MJO and convectively coupled equatorial waves simulated by CMIP5 climate models. J Climate 26:6185–6214
Jackson B, Nicholson SE, Klotter D (2009) Mesoscale convective systems over western equatorial Africa and their relationship to large-scale circulation. Mon Weather Rev 137:1272–1294
Jiang Y, Zhou L, Tucker CJ, Raghavendra A, Hua W, Liu Y, Joiner J (2019) Widespread increase of boreal summer dry season length over the Congo rainforest. Nat Climate Change 9:617–622
Knapp KR (2008) Scientific data stewardship of International Satellite Cloud Climatology Project B1 global geostationary observations. J Appl Remote Sens 2:023548
Knapp KR et al (2011) Globally gridded satellite observations for climate studies. Bull Am Meteorol Soc 92:893–907
LaFleur DM, Barrett BS, Henderson GR (2015) Some climatological aspects of the Madden–Julian Oscillation (MJO). J Climate 28:6039–6053
Lee DE, Biasutti M (2014) Climatology and variability of precipitation in the twentieth-century reanalysis. J Climate 27:5964–5981
Lewis SL (2006) Tropical forests and the changing earth system. Philos Trans R Soc Lond B 361:195–210
Lewis SL et al (2009) Increasing carbon storage in intact African tropical forests. Nature 457:1003–1006
Madden R, Julian P (1971) Detection of a 40–50 day oscillation in the zonal wind in the tropical Pacific. J Atmos Sci 28:702–708
Madden R, Julian P (1972) Description of global-scale circulation cells in the tropics with a 40–50 day period. J Atmos Sci 29:1109–1123
McGill R, Tukey JW, Larsen WA (1978) Variations of boxplots. Am Stat 32:12–16
Nicholson SE (2018) The ITCZ and the seasonal cycle over equatorial Africa. Bull Am Meteorol Soc 30:337–348
Nicholson SE, Klotter D, Dezfuli AK, Zhou L (2018) New rainfall datasets for the Congo Basin and surrounding regions. J Hydrometeorol 19:1379–1396
Pohl B, Camberlin P (2006a) Influence of the Madden–Julian Oscillation on East African rainfall. I: intraseasonal variability and regional dependency. Q J R Meteorol Soc 132:2521–2539
Pohl B, Camberlin P (2006b) Influence of the Madden–Julian oscillation on East Africa rainfall. II: March–May season extremes and interannual variability. Q J Roy Meteorol Soc 132:2541–2558
Pohl B, Dieppois B, Crétat J, Lawler D, Rouault M (2018) From synoptic to interdecadal variability in Southern African rainfall: toward a unified view across time scales. J Climate 31:5845–5872
Raghavendra A, Zhou L, Schiraldi NJ, Roundy PE (2017) MJO phase speed and rainfall variability over the Congo rainforest. In: Fifth symposium on prediction of the madden-julian oscillation: processes, prediction and impact Poster#355 American Meteorological Society. https://ams.confex.com/ams/97Annual/webprogram/Paper302854.html
Raghavendra A, Zhou L, Jiang Y, Hua W (2018) Increasing extent and intensity of thunderstorms observed over the Congo Basin from 1982 to 2016. Atmos Res 213:17–26
Raghavendra A, Roundy PE, Zhou L (2019) Trends in tropical wave activity from 1980s–2016. J Climate 32:1661–1676
Roundy PE (2012) Observed structure of convectively coupled waves as a function of equivalent depth: Kelvin waves and the Madden–Julian oscillation. J Atmos Sci 69:2097–2106
Roundy PE (2017) Diagnosis of seasonally varying regression slope coefficients and application to the MJO. Q J Roy Meteorol Soc 143:1946–1952
Schlueter A, Fink AH, Knippertz P, Vogel P (2019a) A systematic comparison of tropical waves over Northern Africa. Part I: influence on rainfall. J Climate 32:1501–1523
Schlueter A, Fink AH, Knippertz P (2019b) A systematic comparison of tropical waves over northern Africa. Part II: dynamics and thermodynamics. J Climate 32:2605–2625
Sinclaire Z, Lenouob A, Tchawouaa C, Janicotc S (2015) Synoptic Kelvin type perturbation waves over Congo basin over the period 1979–2010. J Atmos Sol Terr Phys 130–131:43–46
Sultan B, Janicot S (2003) West African monsoon dynamics. Part II: the “pre-onset” and the “onset” of the summer monsoon. J Climate 16:3407–3427
Taylor KE, Stouffer RJ, Meehl GA (2012) An overview of CMIP5 and the experiment design. Bull Am Meteorol Soc 93:495–498
Taylor CM et al (2017) Frequency of extreme Sahelian storms tripled since 1982 in satellite observations. Nature 544:475–478
Taylor CM et al (2018) Earlier seasonal onset of intense Mesoscale Convective Systems in the Congo Basin since 1999. Geophys Res Lett 45:13458–13467
Ventrice MJ, Thorncroft CD, Janiga MA (2012) Atlantic tropical cyclogenesis: a three-way interaction between an African easterly wave, diurnally varying convection, and a convectively coupled atmospheric Kelvin wave. Mon Weather Rev 140:1108–1124
Washington R, James R, Pearce H, Pokam WM, Moufouma-Okia W (2013) Congo Basin rainfall climatology: can we believe the climate models? Philos Trans R Soc B 368:20120296
Wheeler MC, Hendon HH (2004) An all-season real-time multivariate MJO index: development of an index for monitoring and prediction. Mon Weather Rev 132:1917–1932
Wheeler M, Kiladis GN (1999) Convectively coupled equatorial waves: analysis of clouds and temperature in the wavenumber–frequency domain. J Atmos Sci 56:374–399
Zaitchik BF (2016) Madden–Julian Oscillation impacts on tropical African precipitation. Atmos Res 184:88–102
Zhang C, Dong M (2004) Seasonality of the Madden–Julian oscillation. J Climate 17:3169–3180
Zhou L et al (2014) Widespread decline of Congo rainforest greenness in the past decade. Nature 509:86–90
Zipser E, Liu C, Cecil D, Nesbitt S, Yorty D (2006) Where are the most intense thunderstorms on Earth? Bull Am Meteorol Soc 87:1057–1071
Acknowledgements
Authors AR, LZ, and YJ were supported by National Science Foundation (NSF AGS-1535426 and AGS-1854486). PR would like to acknowledge the support received from NSF AGS-1128779 and AGS-1358214. We thank Dr. Susanna Corti for serving as the Editor of this paper, and two anonymous reviewers for their constructive feedback which greatly improved the quality of this paper.
Author information
Authors and Affiliations
Corresponding author
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
About this article
Cite this article
Raghavendra, A., Zhou, L., Roundy, P.E. et al. The MJO’s impact on rainfall trends over the Congo rainforest. Clim Dyn 54, 2683–2695 (2020). https://doi.org/10.1007/s00382-020-05133-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00382-020-05133-5