@article{fdi:010035757,
  title = {{A}frican {E}asterly {W}aves and convective activity in wet and dry sequences of the {W}est {A}frican {M}onsoon},
  author = {{L}avaysse, {C}hristophe and {D}iedhiou, {A}rona and {L}aurent, {H}enry and {L}ebel, {T}hierry},
  editor = {},
  language = {{ENG}},
  abstract = {{J}anicot and {S}ultan ({G}eophys {R}es {L}ett 28(3):523-526, 2001) and {S}ultan et al. ({J} {C}lim 16(21):3389-3406, 2003) showed evidence of an intra-seasonal signal of {S}ahelian rainfall corresponding to wet and dry sequences of the {W}est {A}frican {M}onsoon. {U}sing {NCEP}/{NCAR} reanalysis, {NOAA} outgoing longwave radiation ({OLR}) and observed daily rainfall over {W}est {A}frica from 1968 to 1990, this paper investigates the variability of 3 to 5-day {A}frican {E}asterly {W}aves ({AEW}s),. convection and their relationship with rainfall in these wet and dry sequences. {T}he mean daily value rainfall during wet sequences is twice the mean value during dry sequences but the number of dry or wet sequences per year is not correlated with the annual rainfall. {W}et sequences account for 39% of the annual accumulated rainfall while dry sequences account for 22%. {T}he number of 3 to 5-day {AEW}s increases during wet years in wet sequences and the activity tends to be larger during wet years in both wet and dry sequences. {T}hese {AEW}s explain 40% of the accumulated rainfall during wet sequences whereas they contribute to 26% of the accumulated rainfall observed during dry sequences. {G}enerally, they contribute to the increase of rainfall during these sequences. {M}ean convection is stronger and there are twice as many low {OLR} days (<225{W}/m(2)) during wet than dry sequences. {T}he mean rainfall for days with high convective activity (convective days) is also twice as great during wet sequences. {R}ainfall that occurs during days without low {OLR} (weak convection with warm cloud tops or isolated deep convection) contributes to 69% of the total rainfall during dry sequences and 45% during wet sequences. {A} composite study was performed from day {D}-0-10 to day {D}-o + 10 in each sequence. {W}et (dry) sequences of the {A}frican monsoon start with a decrease (slight increase) of the negative meridional {E}rtel {P}otential {V}orticity ({PV}) gradient at 700 h{P}a, associated with an increase (decrease) of the spectral density of {AEW}s. {D}uring the wet sequence, the {A}frican {E}asterly {J}et ({AEJ}), detected by 700 h{P}a zonal wind, decreases and moves northward, whereas the {T}ropical {E}asterly {J}et ({TEJ}), detected at 200 h{P}a, increases and shifts southward. {C}onvective activity increases from {D}-0-6 to {D}-0-3 and remains high for 4 days in wet sequences. {T}he daily rainfall increases (decreases) between {D}-0-6 and {D}-0 and returns to the mean value at {D}-0 + 4 for wet (dry) sequences.},
  keywords = {},
  booktitle = {},
  journal = {{C}limate {D}ynamics},
  volume = {27},
  numero = {2-3},
  pages = {319--332},
  ISSN = {0930-7575},
  year = {2006},
  DOI = {10.1007/s00382-006-0137-5},
  URL = {https://www.documentation.ird.fr/hor/fdi:010035757},
}