The influence of atmospheric water content, temperature, and aerosol optical depth on downward longwave radiation in arid conditions

Abstract. Water uptake can significantly increase the size and therefore 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) Atlantic Inflow progression phase (15–2 UTC), when winds from the Gulf of Guinea accelerate in the less turbulent evening and nighttime boundary layer, (b) Moist morning phase (3–8 UTC), when the passage of the Atlantic Inflow front leads to overall cool and moist conditions over land and (c) Daytime drying phase (9–15 UTC), in which the Atlantic Inflow front re-establishes with the inland heating initiated after sunrise. This diurnal cycle imprints, via the relative humidity, also 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, the 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 of 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.

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Study of total column atmospheric aerosol optical depth, ozone and precipitable water content over Bay of Bengal during BOBMEX-99

Journal of Earth System Science ◽

10.1007/bf02701987 ◽

2003 ◽

Vol 112 (2) ◽

pp. 205-221 ◽

Cited By ~ 7

Author(s):

K. K. Dani ◽

R. S. Maheskumar ◽

P. C. S. Devara

Keyword(s):

Water Content ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Bay Of Bengal ◽

Atmospheric Aerosol ◽

Precipitable Water ◽

Precipitable Water Content ◽

Total Column

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Radiative and thermodynamic responses to aerosol extinction profiles during the pre-monsoon month over South Asia

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-16901-2015 ◽

2015 ◽

Vol 15 (12) ◽

pp. 16901-16943 ◽

Cited By ~ 2

Author(s):

Y. Feng ◽

V. R. Kotamarthi ◽

R. Coulter ◽

C. Zhao ◽

M. Cadeddu

Keyword(s):

Boundary Layer ◽

South Asia ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Lower Troposphere ◽

Longwave Radiation ◽

Radiative Heating ◽

Lower Atmosphere ◽

Radiative Effects ◽

Aerosol Radiative

Abstract. Aerosol radiative effects and thermodynamic responses over South Asia are examined with a version of the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) for March 2012. Model results of Aerosol Optical Depth (AOD) and extinction profiles are analyzed and compared to satellite retrievals and two ground-based lidars located in the northern India. The WRF-Chem model is found to underestimate the AOD during the simulated pre-monsoon month and about 83 % of the model low-bias is due to aerosol extinctions below ~2 km. Doubling the calculated aerosol extinctions below 850 hPa generates much better agreement with the observed AOD and extinction profiles averaged over South Asia. To separate the effect of absorption and scattering properties, two runs were conducted: in one run (Case I), the calculated scattering and absorption coefficients were increased proportionally, while in the second run (Case II) only the calculated aerosol scattering coefficient was increased. With the same AOD and extinction profiles, the two runs produce significantly different radiative effects over land and oceans. On the regional mean basis, Case I generates 48 % more heating in the atmosphere and 21 % more dimming at the surface than Case II. Case I also produces stronger cooling responses over the land from the longwave radiation adjustment and boundary layer mixing. These rapid adjustments offset the stronger radiative heating in Case I and lead to an overall lower-troposphere cooling up to −0.7 K day−1, which is smaller than that in Case II. Over the ocean, direct radiative effects dominate the heating rate changes in the lower atmosphere lacking such surface and lower atmosphere adjustments due to fixed sea surface temperature, and the strongest atmospheric warming is obtained in Case I. Consequently, atmospheric dynamics (boundary layer heights and meridional circulation) and thermodynamic processes (water vapor and cloudiness) are shown to respond differently between Case I and Case II underlying the importance of determining the exact portion of scattering or absorbing aerosols that lead to the underestimation of aerosol optical depth in the model. In addition, the model results suggest that both direct radiative effect and rapid thermodynamic responses need to be quantified for understanding aerosol radiative impacts.

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Some features of columnar aerosol optical depth, ozone and precipitable water content observed over land during the INDOEX-IFP99

Meteorologische Zeitschrift ◽

10.1127/0941-2948/2001/0010-0123 ◽

2001 ◽

Vol 10 (2) ◽

pp. 123-130 ◽

Cited By ~ 18

Author(s):

Panuganti China Sattilingam Devara ◽

Rajamma Sukumaran Maheskumar ◽

Pulidindi Ernest Raj ◽

Kundan Krishnarao Dani ◽

Sunil Manohar Sonbawne

Keyword(s):

Water Content ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Precipitable Water ◽

Precipitable Water Content

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Temporal Variations in Atmospheric Water Vapor and Aerosol Optical Depth Determined by Remote Sensing

Journal of Applied Meteorology ◽

10.1175/1520-0450(1977)016<1312:tviawv>2.0.co;2 ◽

1977 ◽

Vol 16 (12) ◽

pp. 1312-1321 ◽

Cited By ~ 19

Author(s):

David E. Pitts ◽

W. E. McAllum ◽

Michael Heidt ◽

Keith Jeske ◽

J. T. Lee ◽

...

Keyword(s):

Remote Sensing ◽

Water Vapor ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Temporal Variations ◽

Atmospheric Water Vapor ◽

Atmospheric Water

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-14271-2018 ◽

2018 ◽

Vol 18 (19) ◽

pp. 14271-14295 ◽

Cited By ~ 10

Author(s):

Konrad Deetz ◽

Heike Vogel ◽

Sophie Haslett ◽

Peter Knippertz ◽

Hugh Coe ◽

...

Keyword(s):

Relative Humidity ◽

Water Content ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Diurnal Cycle ◽

Liquid Water ◽

Liquid Water Content ◽

Scale Model ◽

Model Framework ◽

The Impact

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.

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STUDIES ON THE TOTAL COLUMN ATMOSPHERIC AEROSOL OPTICAL DEPTH, OZONE AND PRECIPITABLE WATER CONTENT IN THE TROPICS: A CASE STUDY OF MALAYSIA

Photon: Jurnal Sain dan Kesehatan ◽

10.37859/jp.v1i2.117 ◽

2011 ◽

Vol 1 (2) ◽

pp. 55-62

Author(s):

Said Fhazli

Keyword(s):

Water Vapor ◽

Water Content ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Precipitable Water ◽

Mean Value ◽

Total Column Ozone ◽

Precipitable Water Content ◽

The Mean ◽

Total Column

A Multifilter Rotating Shadowband Radiometer has been used to monitor the directly transmitted solar irradiance at six wavelength regions (413.9 nm, 494.6 nm, 612.7 nm, 670.8 nm, 868.0 nm and 939.1 nm) for three clear stable days at Bangi. Extensive observations of the columnar aerosol optical depth (AOD), total column ozone (TCO) and precipitable water content (PWC) have been carried out using this instrument. The result shows that the maximum optical depth of aerosol at the shorter wavelength, especially on 24th February 2002 with mean value of 0.254 (24th February 2002), 0.095 (25th February 2002), and 0.072 (26th February 2002) while the ozone optical depth shows the mean value 0.0153 on 24th February 2002, 0.0174 on 25thFebruary 2002 and 0.0175 on 26th February 2002 with the avarage absorption coefficient (a), 0.2 (24th and 26th February 2002) and 0.1 (25th February 2002). The mean value of water vapor content shows that  = 0.356 cm and k = 0.301 cm for wavelength 939.1 nm. From the aerosol optical depth, it shows the existence of smoke type of aerosol on February, 24th to 25th 2002 with Ångström coefficient, , is 1.534 and 1.5513, respectively, and sea water vapor is 0.9889 on 26thFebruary 2002. From the Ångström coefficient, it shows that atmosphere layer of Bangi at that moment is similar to U.S. Standard Atmosphere, with maximum spectral irradiance on black body temperature is 5860 oK.

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