Scale decomposition of atmospheric water budget over West Africa during the monsoon 2006 from NCEP/GFS analyses

2009 ◽  
Vol 35 (1) ◽  
pp. 143-157 ◽  
Author(s):  
Soline Bielli ◽  
Remy Roca
Keyword(s):  
West Africa ◽  
Water Budget ◽  
Atmospheric Water

scholarly journals A GCM study of the response of the atmospheric water cycle of West Africa and the Atlantic to Saharan dust radiative forcing

2009 ◽  
Vol 27 (10) ◽  
pp. 4023-4037 ◽  
Author(s):  
K. M. Lau ◽  
K. M. Kim ◽  
Y. C. Sud ◽  
G. K. Walker
Keyword(s):  
West Africa ◽  
Radiative Forcing ◽  
Large Scale ◽  
Water Cycle ◽  
Deep Convection ◽  
Saharan Dust ◽  
Caribbean Region ◽  
Atmospheric Water ◽  
The West ◽  
Dust Layer

Abstract. The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence of an "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summer, as a result of large-scale atmospheric feedback triggered by absorbing dust aerosols, rainfall and cloudiness are enhanced over the West Africa/Eastern Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while longwave has the opposite response. The elevated dust layer warms the air over West Africa and the eastern Atlantic. As the warm air rises, it spawns a large-scale onshore flow carrying the moist air from the eastern Atlantic and the Gulf of Guinea. The onshore flow in turn enhances the deep convection over West Africa land, and the eastern Atlantic. The condensation heating associated with the ensuing deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in a northward shift of the West Africa precipitation over land, increased low-level westerly flow over West Africa at the southern edge of the dust layer, and a near surface westerly jet underneath the dust layer over the Sahara. The dust radiative forcing also leads to significant changes in surface energy fluxes, resulting in cooling of the West African land and the eastern Atlantic, and warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at 0.95 or higher.

scholarly journals Implications of Improved Representation of Convection for the East Africa Water Budget Using a Convection-Permitting Model

2019 ◽  
Vol 32 (7) ◽  
pp. 2109-2129 ◽  
Author(s):  
Declan L. Finney ◽  
John H. Marsham ◽  
Lawrence S. Jackson ◽  
Elizabeth J. Kendon ◽  
David P. Rowell ◽  
...  
Keyword(s):  
East Africa ◽  
Water Budget ◽  
Large Scale ◽  
Lake Victoria ◽  
Regional Climate ◽  
Moisture Flux ◽  
Land Breeze ◽  
Moist Convection ◽  
Atmospheric Water ◽  
Lake Victoria Basin

Abstract The precipitation and diabatic heating resulting from moist convection make it a key component of the atmospheric water budget in the tropics. With convective parameterization being a known source of uncertainty in global models, convection-permitting (CP) models are increasingly being used to improve understanding of regional climate. Here, a new 10-yr CP simulation is used to study the characteristics of rainfall and atmospheric water budget for East Africa and the Lake Victoria basin. The explicit representation of convection leads to a widespread improvement in the intensities and diurnal cycle of rainfall when compared with a parameterized simulation. Differences in large-scale moisture fluxes lead to a shift in the mean rainfall pattern from the Congo to Lake Victoria basin in the CP simulation—highlighting the important connection between local changes in the representation of convection and larger-scale dynamics and rainfall. Stronger lake–land contrasts in buoyancy in the CP model lead to a stronger nocturnal land breeze over Lake Victoria, increasing evaporation and moisture flux convergence (MFC), and likely unrealistically high rainfall. However, for the mountains east of the lake, the CP model produces a diurnal rainfall cycle much more similar to satellite estimates, which is related to differences in the timing of MFC. Results here demonstrate that, while care is needed regarding lake forcings, a CP approach offers a more realistic representation of several rainfall characteristics through a more physically based realization of the atmospheric dynamics around the complex topography of East Africa.

How is the atmospheric residence time of evapotranspired water altered with a dried-up lake or a forest restoration scenario and what is the impact on precipiation?

2021 ◽  
Author(s):  
Jianhui Wei ◽  
Joël Arnault ◽  
Zhenyu Zhang ◽  
Patrick Laux ◽  
Benjamin Fersch ◽  
...  
Keyword(s):  
Land Use ◽  
Residence Time ◽  
Water Budget ◽  
Forest Restoration ◽  
Water Cycle ◽  
Wrf Model ◽  
Atmospheric Water ◽  
Budget Analysis ◽  
Precipitation Recycling ◽  
The Impact

<p>Land surface characteristics and processes may have complex interactions with the physical and dynamical processes of the atmosphere. However, adequate methods for systemically understanding individual processes of the nonlinearly coupled land-atmosphere continuum are still rare. Therefore, in this study, the age-weighted evaporation tagging approach of Wei et al. (2016) and the three-dimensional online atmospheric water budget analysis of Arnault et al. (2016) were implemented into the Weather Research and Forecast (WRF) model. In addition to the total and tagged atmospheric water states of matter, the latter approach was further extended for age-weighted tagged atmospheric water states of matter, thereby providing a prognostic equation of the residence time of state variables in the atmospheric water cycle.<strong> </strong>This extension allows to systematically quantify the fate of evaporated and transpired water in terms of magnitude, location, composition, and residence time. The extended WRF model was tested for a land use and land cover change study for the Poyang Lake basin, the largest freshwater lake in China. Two hypothetical scenarios, i.e., a dried-up lake and a forest restoration scenario, were simulated and then compared to a real-case control simulation using the original land-use data. The results of the basin-scale precipitation recycling in the context of evapotranspiration partitioning and the modified atmospheric water cycle due to both scenarios will be presented and discussed. We conclude that our newly developed modelling framework and the proposed analysis strategy have the potential to be applied for better understanding and quantifying the nonlinearly intertwined processes between the land and the atmosphere.</p><p>References:</p><p>Arnault, J., Knoche, R., Wei, J., & Kunstmann, H. (2016). Evaporation tagging and atmospheric water budget analysis with WRF: A regional precipitation recycling study for West Africa. Water Resources Research, 52(3), 1544–1567. https://doi.org/10.1002/2015WR017704</p><p>Wei, J., Knoche, R., & Kunstmann, H. (2016). Atmospheric residence times from transpiration and evaporation to precipitation: An age-weighted regional evaporation tagging approach. Journal of Geophysical Research: Atmospheres, 121(12), 6841–6862. https://doi.org/10.1002/2015JD024650</p>

scholarly journals Climatological Basin-Scale Amazonian Evapotranspiration Estimated through a Water Budget Analysis

2008 ◽  
Vol 9 (5) ◽  
pp. 1048-1060 ◽  
Author(s):  
Hanan N. Karam ◽  
Rafael L. Bras
Keyword(s):  
Time Series ◽  
Land Surface ◽  
Water Budget ◽  
Amazon Basin ◽  
Land Surface Models ◽  
Atmospheric Water ◽  
Budget Analysis ◽  
Best Estimate ◽  
Basin Scale ◽  
Surface Models

Abstract Spatially averaged evapotranspiration [ET] over the Amazon Basin is computed as the residual of the basin’s atmospheric water balance equation, at the monthly time scale and for the period 1988–2001. Basin-averaged rainfall [P] is obtained from the Global Precipitation Climatology Project (GPCP) dataset, and alternative estimates of the net convergence of atmospheric water vapor flux over the basin [C] are derived from three global reanalyses: the NCEP–NCAR and NCEP–Department of Energy (DOE) reanalyses and the 40-yr ECMWF Re-Analysis (ERA-40). Additionally, a best estimate of [C] is obtained by taking a weighted average of data from these three sources, in which the weight factors are based on the random error attributed to each reanalysis’ [C] estimates by comparison to river discharge data. The resulting time series is dominated by ERA-40’s contribution, which was found to be the most accurate over the study period. Data products from the three reanalyses are also employed to compute the monthly tendencies of total precipitable water over the basin. While the seasonal signature of this “accumulation term” provides important insight into the Amazon Basin’s hydrological cycle, its magnitude is found to be negligible relative to the other components of the water budget. The value of mean annual [ET] presented in this work is significantly lower than other published estimates that are based on simulations by various land surface models. Furthermore, when the best estimate of [C] is used, the resulting [ET] time series exhibits a seasonal cycle that is in phase with that of basin-averaged surface net radiation, suggesting that Amazonian evapotranspiration is prevalently limited by energy availability. In contrast, most land surface models, including that of the NCEP–NCAR reanalysis, simulate water-limited evapotranspiration in the Amazon Basin. The analysis presented here supports the hypothesis that most Amazonian trees sustain elevated evapotranspiration rates during the dry season through deep roots, which tap into large reservoirs of soil water that are replenished during the following wet season.

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