The El Niño effect on Ethiopian summer rainfall
Tóm tắt
While El Niño is known to cause failure of Kiremt (boreal summer) rainfall in Ethiopia, the mechanisms are not fully understood. Here we use the ECHAM5 Atmospheric General Circulation Model to investigate the physical link between Pacific sea surface temperature (SST) anomalies and Kiremt rainfall. We compare ECHAM5 simulations forced with reconstructed SST data, to gauge-based rainfall observations and atmospheric reanalysis for the time period of 1961–2009. We perform composite analysis and sensitivity experiments driven only with equatorial Pacific SST anomalies. Our results show warm SST anomalies in the equatorial Pacific drive a corresponding large-scale circulation anomaly with subsidence over Ethiopia in dry Kiremt seasons. Horizontal wind fields show a slow-down of the whole Indian monsoon system with a weaker Tropical Easterly Jet and a weaker East African Low-Level Jet in these summers. These changes can be seen as an anomalous circulation cell over northern Africa with westerlies at 100–200 hPa and easterlies below 500 hPa. Surface easterlies might reduce the moisture inflow from the Atlantic and Congo basin into Ethiopia. This and the general subsidence over the region could explain the reduction in Kiremt rainfall. Our results suggest up to 50% of the Kiremt rainfall anomalies is driven by equatorial Pacific SST variability.
Tài liệu tham khảo
Äthiopien - Wirtschaft. Auswärtiges Amt - Deutschland. Accessed Sept 2015
Beltrando G, Camberlin P (1993) Interannual variability of rainfall in the eastern horn of Africa and indicators of atmospheric circulation. Int J Climatol 13:533–546. doi:10.1002/joc.3370130505
Berhane F, Zaitchik B, Dezfuli A (2013) Subseasonal analysis of precipitation variability in the Blue Nile River Basin. J Clim 27:325–344. doi:10.1175/JCLI-D-13-00094.1
Camberlin P (1997) Rainfall anomalies in the source region of the Nile and their connection with the Indian summer monsoon. J Clim 10:1380–1392. doi:10.1175/1520-0442(1997)010<1380:RAITSR>2.0.CO;2
Camberlin P (2009) Nile basin climates. In: Dumont H (ed) The Nile, vol 89., Monographiae BiologicaeSpringer, Dordrecht, pp 307–333. doi:10.1007/978-1-4020-9726-3_16
Camberlin P, Philippon N (2002) The East African march–may rainy season: associated atmospheric dynamics and predictability over the 1968–97 period. J Clim 15:1002–1019. doi:10.1175/1520-0442(2002)015<1002:TEAMMR>2.0.CO;2
Chakraborty A, Behera SK, Mujumdar M, Ohba R, Yamagata T (2006) Diagnosis of tropospheric moisture over Saudi Arabia and influences of IOD and ENSO. Mon Weather Rev 134:598–617. doi:10.1175/MWR3085.1
Copsey D, Sutton R, Knight JR (2006) Recent trends in sea level pressure in the Indian Ocean region. Geophys Res Lett. doi:10.1029/2006GL027175
Dinku T, Hailemariam K, Maidment R, Tarnavsky E, Connor S (2014) Combined use of satellite estimates and rain gauge observations to generate high-quality historical rainfall time series over Ethiopia. Int J Climatol 34:2489–2504. doi:10.1002/joc.3855
Diro GT, Black E, Grimes DIF (2008) Seasonal forecasting of Ethiopian spring rains. Meteorol Appl 15:73–83. doi:10.1002/met.63
Diro GT, Grimes DIF, Black E (2011a) Large scale features affecting Ethiopian rainfall. In: Williams CJR, Kniveton DR (eds) African climate and climate change, vol 43., Advances in global change researchSpringer, Netherlands, pp 13–50
Diro GT, Grimes DIF, Black E (2011b) Teleconnections between Ethiopian summer rainfall and sea surface temperature: part I—observation and modelling. Clim Dyn 37:103–119. doi:10.1007/s00382-010-0837-8
Diro GT, Toniazzo T, Shaffrey L (2011c) Ethiopian Rainfall in Climate Models. In: Williams RCJ, Kniveton RD (eds) African climate and climate change: physical, social and political perspectives. Springer, Dordrecht, pp 51–69. doi:10.1007/978-90-481-3842-5_3
Gissila T, Black E, Grimes DIF, Slingo JM (2004) Seasonal forecasting of the Ethiopian summer rains. Int J Climatol 24:1345–1358. doi:10.1002/joc.1078
Gleixner S, Keenlyside N, Hodges KI, Tseng W-L, Bengtsson L (2014) An inter-hemispheric comparison of the tropical storm response to global warming. Clim Dyn 42:2147–2157. doi:10.1007/s00382-013-1914-6
Griffiths JF (1972) Ethiopian highlands. In: World survey of climatology, vol 10. Elsevier, Amsterdam. ISBN:0444408932
Hansen JW, Mason SJ, Sun L, Tall A (2011) Review of seasonal climate forecasting for agriculture in Sub-Saharan Africa. Exp Agric 47:205–240. doi:10.1017/S0014479710000876
Holton JR, Hakim GJ (2013) Chapter 10—the general circulation. In: Holton JR, Hakim GJ (eds) An introduction to dynamic meteorology, 5th edn. Academic Press, Boston, pp 325–375
Jiang X et al (2015) Vertical structure and physical processes of the Madden–Julian oscillation: exploring key model physics in climate simulations. J Geophys Res Atmos 120:4718–4748. doi:10.1002/2014JD022375
Kobayashi S et al (2015) The JRA-55 reanalysis: general specifications and basic characteristics. J Meteorol Soc Jpn 93:5–48. doi:10.2151/jmsj.2015-001
Korecha D, Barnston AG (2007) Predictability of June–September rainfall in Ethiopia. Mon Weather Rev 135:628–650. doi:10.1175/MWR3304.1
Korecha D, Sorteberg A (2013a) Construction of homogeneous rainfall regimes for Ethiopia. Submitted to Int J Climatol
Korecha D, Sorteberg A (2013b) Validation of operational seasonal rainfall forecast in Ethiopia. Water Resour Res 49:7681–7697. doi:10.1002/2013wr013760
Kucharski F, Bracco A, Yoo JH, Molteni F (2007) Low-frequency variability of the Indian monsoon–ENSO relationship and the tropical Atlantic: the “weakening” of the 1980s and 1990s. J Clim 20:4255–4266. doi:10.1175/JCLI4254.1
Maidment RI et al (2014) The 30 year TAMSAT African rainfall climatology and time series (TARCAT) data set. J Geophys Res Atmos 119:10619–10644. doi:10.1002/2014jd021927
Mohamed YA, van den Hurk BJJM, Savenije HHG, Bastiaanssen WGM (2005) Hydroclimatology of the Nile: results from a regional climate model. Hydrol Earth Syst Sci 9:263–278. doi:10.5194/hess-9-263-2005
Mohino E et al (2011) Changes in the interannual SST-forced signals on West African rainfall. AGCM intercomparison. Clim Dyn 37:1707–1725. doi:10.1007/s00382-011-1093-2
Mutai CC, Ward MN, Colman AW (1998) Towards the prediction of the East Africa short rains based on sea-surface temperature-atmosphere coupling. Int J Climatol 18:975–997. doi:10.1002/(sici)1097-0088(199807)18:9<975:aid-joc259>3.3.co;2-l
Otieno V, Anyah R (2013) CMIP5 simulated climate conditions of the Greater Horn of Africa (GHA). Part 1: contemporary climate. Clim Dyn 41:2081–2097. doi:10.1007/s00382-012-1549-z
Peixoto JP (1992) Physics of climate. Melville, American Institute of Physics New York
Roeckner E et al (2003) The atmospheric general circulation model ECHAM 5. Part I. Model description. Max-Planck-Institute for Meteorology, Hamburg
Sperber KR et al (2013) The Asian summer monsoon: an intercomparison of CMIP5 vs. CMIP3 simulations of the late 20th century. Clim Dyn 41:2711–2744. doi:10.1007/s00382-012-1607-6
Segele ZT, Lamb PJ (2005) Characterization and variability of Kiremt rainy season over Ethiopia. Meteorol Atmos Phys 89:153–180
Segele ZT, Lamb PJ, Leslie LM (2009a) Large-scale atmospheric circulation and global sea surface temperature associations with Horn of Africa June–September rainfall. Int J Climatol 29:1075–1100
Segele ZT, Leslie LM, Lamb PJ (2009b) Evaluation and adaptation of a regional climate model for the Horn of Africa: rainfall climatology and interannual variability. Int J Climatol 29:47–65. doi:10.1002/joc.1681
Segele ZT, Leslie LM, Tarhule A (2015) Sensitivity of horn of Africa rainfall to regional sea surface temperature forcing. J Clim 3:365
Seleshi Y, Demaree GR (1995) Rainfall variability in the Ethiopian and Eritrean highlands and its links with the southern oscillation index. J Biogeogr 22:945–952. doi:10.2307/2845995
Shaman J, Tziperman E (2007) Summertime ENSO–North African-Asian Jet teleconnection and implications for the Indian monsoons. Geophys Res Lett. doi:10.1029/2006GL029143
Smith TM, Reynolds RW, Peterson TC, Lawrimore J (2008) Improvements to NOAA’s historical merged land–ocean surface temperature analysis (1880–2006). J Clim 21:2283–2296. doi:10.1175/2007JCLI2100.1
Tiedtke M (1996) An extension of cloud-radiation parameterization in the ECMWF model: the representation of subgrid-scale variations of optical depth. Mon Weather Rev 124:745–750. doi:10.1175/1520-0493(1996)124<0745:aeocrp>2.0.co;2
Tsegay W-G (1997) El Niño and drought early warning in Ethiopia. Internet J Afr Stud 2. Available at http://www.bradford.ac.uk/researchold/ijas/ijasno2/Georgis.html
Tseng W-L (2012) Role of ocean-atmosphere interaction for tropical climate variability over warm pool regions. Doctoral Thesis, Christian-Albrechts-Universität Kiel
Viste E, Sorteberg A (2013) The effect of moisture transport variability on Ethiopian summer precipitation. Int J Climatol 33:3106–3123
Viste E, Korecha D, Sorteberg A (2013) Recent drought and precipitation tendencies in Ethiopia. Theor Appl Climatol 112:535–551. doi:10.1007/s00704-012-0746-3
Von Storch H, Zwiers FW (2001) Statistical analysis in climate research. Cambridge University Press, Cambridge