@article{PAR00001879,
  title = {{C}haracterization of the diurnal cycle of the {W}est {A}frican monsoon around the monsoon onset},
  author = {{S}ultan, {B}enjamin and {J}anicot, {S}erge and {D}robinski, {P}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}his study investigates the diurnal cycle of the {W}est {A}frican monsoon and its seasonal modulation with particular focus on the monsoon onset period. {A} composite analysis around the monsoon onset date is applied to the 1979-2000 {NCEP}-{DOE} reanalysis and 40-yr {ECMWF} {R}e-{A}nalysis ({ERA}-40) at 0000, 0600, 1200, and 1800 {UTC}. {T}his study points out two independent modes describing the space-time variability of the diurnal cycle of low-level wind and temperature. {W}hile the first mode appears to belong to a gradual and seasonal pattern linked with the northward migration of the whole monsoon system, the second mode is characterized by more rapid time variations with a peak of both temperature and wind anomalies around the monsoon onset date. {T}his latter mode is connected with the time pattern of a nocturnal jet reaching its highest values around the onset date. {T}he diurnal cycle of dry and deep convection is also investigated through the same method. {A} distinct diurnal cycle of deep convection in the {ITCZ} is evidenced with a peak at 1200 {UTC} before the monsoon onset, and at 1800 {UTC} after the monsoon onset. {S}trong ascending motions associated with deep convection may generate a gravity wave that propagates northward and reaches the {S}aharan heat low region 12 h later. {T}he diurnal cycle of the dry convection in the {S}aharan heat low is similar during the preonset and the postonset periods with a peak at night (0000 {UTC}) consistent with the nocturnal jet intensification. {T}his convection is localized at 15 degrees and 20 degrees {N} before and after the monsoon onset, respectively. {B}oth during the first rainy season in spring and the monsoon season in summer, the nocturnal jet brings moisture in the boundary layer north of the {ITCZ} favoring humidification and initiation of new convective cells, helping the northward progression of the {ITCZ}. {A}t the end of the {S}ummer the southward return of the {ITCZ} is associated with the disappearance of the core of the monsoon jet. {D}espite a lot of similarities between the results obtained using {NCEP}-{DOE} and {ERA}-40 reanalyses, giving confidence in the significance of these results, some differences are identified, especially in the diurnal cycle of deep convection, which limit the interpretation of some of these results and highlight discrepancies in the reanalyses.},
  keywords = {},
  booktitle = {},
  journal = {{J}ournal of {C}limate},
  volume = {20},
  numero = {15},
  pages = {4014--4032},
  ISSN = {0894-8755},
  year = {2007},
  DOI = {10.1175/{JCLI}4218.1},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00001879},
}