The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southernWest Africa

Haslett, Sophie L.; Taylor, Jonathan; Deetz, Konrad; Vogel, Bernhard; Babić, Karmen; Kalthoff, Norbert; Dione, Cheikh; Lohou, Fabienne; Brito, Joel; Dupuy, Régis; Schwarzenböeck, Alfons; Coe, Hugh

doi:10.5194/acp-2018-805

Cited by 3 publications

(4 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The study of Haslett et al (2018), which is currently under review and derives the ALWC solely based on measurements by using aircraft observations, radiosonde data and the ZSR mixing rule, comes to similar conclusions with respect to the aerosol properties and the ALWC-related AOD increase.…”

Section: Discussionmentioning

confidence: 80%

“…; only for organic aerosol is an increase with height visible. The DACCIWA aircraft observations also reveal a general dominance of organic aerosol (e.g., Haslett et al, 2018). Biomass burning is an important source of organic aerosol and is likely responsible for the dominance of organic aerosol over the Ivory Coast.…”

Section: Impact Of Relative Humidity (Rh)mentioning

confidence: 93%

“…The ALWC is derived by using the Zdanovskii, Stokes and Robinson (ZSR) mixing rule (Stokes and Robinson, 1966). Hygroscopicity measurements can be obtained, e.g., via the high-humidity tandem differential mobility analyzer (HH-TDMA; Hennig et al, 2005) for 90-98.5 % RH. Estimations of aerosol hygroscopicity are also possible via the combination of observed aerosol number size distributions and aerosol compositions from aerosol mass spectrometers.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Aerosol liquid water content in the moist southern West African monsoon layer and its radiative impact

et al. 2018

Self Cite

View full text Add to dashboard Cite

Abstract. Water uptake can significantly increase the size and therefore alters the optical properties of aerosols. In this study, the regional-scale model framework COSMO-ART is applied to southern West Africa (SWA) for a summer monsoon process study on 2–3 and 6–7 July 2016. The high moisture and aerosol burden in the monsoon layer makes SWA favorable to quantify properties that determine the aerosol liquid water content and its impact on radiative transfer. Given the marked diurnal cycle in SWA, the analysis is separated into three characteristic phases: (a) the Atlantic inflow progression phase (15:00–02:00 UTC), when winds from the Gulf of Guinea accelerate in the less turbulent evening and nighttime boundary layer, (b) the moist morning phase (03:00–08:00 UTC), when the passage of the Atlantic inflow front leads to overall cool and moist conditions over land, and (c) the daytime drying phase (09:00–15:00 UTC), in which the Atlantic inflow front reestablishes with the inland heating initiated after sunrise. This diurnal cycle also impacts, via relative humidity, the aerosol liquid water content. We analyzed the impact of relative humidity and clouds on the aerosol liquid water content. As shown by other studies, accumulation-mode particles are the dominant contributor of aerosol liquid water. We find aerosol growth factors of 2 (4) for submicron (coarse-mode) particles, leading to a substantial increase in mean aerosol optical depth from 0.2 to 0.7. Considering the aerosol liquid water content leads to a decrease in shortwave radiation of about 20 W m−2, while longwave effects appear to be insignificant, especially during nighttime. The estimated relationships between total column aerosol liquid water and radiation are -305±39 W g−1 (shortwave in-cloud), -114±42 W g−1 (shortwave off-cloud) and about −10 W g−1 (longwave). The results highlight the need to consider the relative humidity dependency of aerosol optical depth in atmospheric models, particularly in moist tropical environments where their effect on radiation can be very large.

show abstract

Section: Discussionmentioning

confidence: 80%

Section: Impact Of Relative Humidity (Rh)mentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Aerosol liquid water content in the moist southern West African monsoon layer and its radiative impact

et al. 2018

Self Cite

View full text Add to dashboard Cite

show abstract

“…This is most likely related to the aerosol hygroscopic growth, i.e. the size and composition of particles change due to their water vapor uptake (Deetz et al, 2018a;Haslett et al, 2018). The beginning of the Jet phase is associated with a slight increase of specific humidity, which afterwards does not change considerably until 23:00 UTC, when it even decreases.…”

mentioning

confidence: 99%

The observed diurnal cycle of nocturnal low-level stratus clouds over southern West Africa: a case study

Babić

Adler

Kalthoff

et al. 2018

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract. This study presents the first detailed observational analysis of the complete diurnal cycle of stratiform low-level clouds (LLC) and involved atmospheric processes over southern West Africa. The data used here were collected during the comprehensive DACCIWA (Dynamics-Aerosol-Chemistry-Cloud-Interactions in West Africa) ground-based campaign, which aimed at monitoring LLC characteristics and capturing the wide range of atmospheric conditions related to the West African monsoon flow. In this study, in-situ and remote sensing measurements from the supersite near Savè (Benin) collected during a 5 typical day, which is characterized by the onset of a nocturnal low-level jet (NLLJ) and the formation of LLC, are analyzed.The associated dynamic and thermodynamic conditions allow the identification of five different phases of the LLC diurnal cycle: the Stable, Jet, Stratus I, Stratus II and Convective phase. The analysis of relative humidity tendency shows that cooling is a dominant process for LLC formation, which leads to a continuous increase of relative humidity at a maximum rate of 6 % per hour, until finally saturation is reached and LLC form with a cloud-base height near the height of NLLJ maximum. 10Results of heat budget analysis illustrate that horizontal cold air advection, related to the maritime inflow, which brings the cool maritime air mass and a prominent NLLJ wind profile, has the dominant role on the observed strong cooling of −1.2 K per hour during the Jet phase. The contribution from horizontal cold advection is quantified to be up to 72 %, while radiative cooling and sensible heat flux divergence contribute with 16 and 12 %, respectively, to the observed heat budget below the NLLJ maximum. After the LLC form (Stratus phase I and II), turbulent mixing is an important factor leading to the cooling 15 below the cloud base, while strong radiative cooling at the cloud top helps to maintain thick stratus.

show abstract

The observed diurnal cycle of low-level stratus clouds over southern West Africa: a case study

et al. 2019

Self Cite

View full text Add to dashboard Cite

Abstract. This study presents the first detailed observational analysis of the complete diurnal cycle of stratiform low-level clouds (LLC) and involved atmospheric processes over southern West Africa (SWA). The data used here were collected during the comprehensive DACCIWA (Dynamics-Aerosol-Chemistry-Cloud-Interactions in West Africa) ground-based campaign, which aimed at monitoring LLC characteristics and capturing the wide range of atmospheric conditions related to the West African monsoon flow. In this study, in situ and remote sensing measurements from the supersite near Savè (Benin) collected during a typical day, which is characterized by the onset of a nocturnal low-level jet (NLLJ) and the formation of LLC, are analyzed. The associated dynamic and thermodynamic conditions allow the identification of five different phases related to the LLC diurnal cycle: the stable, jet, stratus I, stratus II, and convective phases. The analysis of relative humidity tendency shows that cooling is a dominant process for LLC formation, which leads to a continuous increase in relative humidity at a maximum rate of 6 % h−1, until finally saturation is reached and LLC form with a cloud-base height near the height of NLLJ maximum. Results of heat budget analysis illustrate that horizontal cold-air advection, related to the maritime inflow, which brings the cool maritime air mass and a prominent NLLJ wind profile, has the dominant role in the observed strong cooling of −1.2 K h−1 during the jet phase. The contribution from horizontal cold advection is quantified to be up to 68 %, while radiative cooling and sensible heat flux divergence both contribute 16 % to the observed heat budget below the NLLJ maximum. After the LLC form (stratus phases I and II), turbulent mixing is an important factor leading to the cooling below the cloud base, while strong radiative cooling at the cloud top helps to maintain thick stratus.

show abstract

The radiative impact of out-of-cloud aerosol hygroscopic growth during the summer monsoon in southernWest Africa

Cited by 3 publications

References 33 publications

Aerosol liquid water content in the moist southern West African monsoon layer and its radiative impact

Aerosol liquid water content in the moist southern West African monsoon layer and its radiative impact

The observed diurnal cycle of nocturnal low-level stratus clouds over southern West Africa: a case study

The observed diurnal cycle of low-level stratus clouds over southern West Africa: a case study

Contact Info

Product

Resources

About