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Markowicz, KM, Flatau PJ, Remiszewska J, Witek M, Reid EA, Reid JS, Bucholtz A, Holben B.  2008.  Observations and modeling of the surface aerosol radiative forcing during UAE(2). Journal of the Atmospheric Sciences. 65:2877-2891.   10.1175/2007jas2555.1   AbstractWebsite

Aerosol radiative forcing in the Persian Gulf region is derived from data collected during the United Arab Emirates (UAE) Unified Aerosol Experiment (UAE(2)). This campaign took place in August and September of 2004. The land -sea-breeze circulation modulates the diurnal variability of the aerosol properties and aerosol radiative forcing at the surface. Larger aerosol radiative forcing is observed during the land breeze in comparison to the sea breeze. The aerosol optical properties change as the onshore wind brings slightly cleaner air. The mean diurnal value of the surface aerosol forcing during the UAE2 campaign is about -20 W m(-2), which corresponds to large aerosol optical thickness (0.45 at 500 nm). The aerosol forcing efficiency [i. e., broadband shortwave forcing per unit optical depth at 550 nm, W m(-2) (tau(500))(-1)] is -53 W m(-2) (tau(500))(-1) and the average single scattering albedo is 0.93 at 550 nm.

Markowicz, KM, Flatau PJ, Ramana MV, Crutzen PJ, Ramanathan V.  2002.  Absorbing mediterranean aerosols lead to a large reduction in the solar radiation at the surface. Geophysical Research Letters. 29   10.1029/2002gl015767   AbstractWebsite

[1] We present direct radiometric observations of aerosol radiative forcing taken during the MINOS experiment (2001) at Finokalia Sampling Station located on North-Eastern shores of Crete, Greece. The mean value of aerosol optical thickness was 0.21 at 500 nm. Aerosols, mostly of anthropogenic origin, lead to a diurnal average reduction of 17.9 W m(-2) in the surface solar radiation, an increase of 11.3 W m(-2) in the atmospheric solar absorption, and an increase of 6.6 W m(-2) in the reflected solar radiation at the top-of-the atmosphere. Thus, the present data gives observational proof for the large role of absorbing aerosols in the Mediterranean. The negative surface forcing and large positive atmospheric forcing values observed for the Mediterranean aerosols is nearly identical to the highly absorbing south Asian haze observed over the Arabian Sea.

Markowicz, KM, Flatau PJ, Kardas AE, Remiszewska J, Stelmaszczyk K, Woeste L.  2008.  Ceilometer retrieval of the boundary layer vertical aerosol extinction structure. Journal of Atmospheric and Oceanic Technology. 25:928-944.   10.1175/2007jtecha1016.1   AbstractWebsite

The CT25K ceilometer is a general-purpose cloud height sensor employing lidar technology for detection of clouds. In this paper it is shown that it can also be used to retrieve aerosol optical properties in the boundary layer. The authors present a comparison of the CT25K instrument with the aerosol lidar system and discuss its good overall agreement for both the range-corrected signals and the retrieved extinction coefficient profiles. The CT25K aerosol profiling is mostly limited to the boundary layer, but it is capable of detecting events in the lower atmosphere such as mineral dust events between 1 and 3 km. Assumptions needed for the estimation of the aerosol extinction profiles are discussed. It is shown that, when a significant part of the aerosol layer is in the boundary layer, knowledge of the aerosol optical depth from a sun photometer allows inversion of the lidar signal. In other cases, surface observations of the aerosol optical properties are used. It is demonstrated that additional information from a nephelometer and aethalometer allows definition of the lidar ratio. Extinction retrievals based on spherical and randomly oriented spheroid assumptions are performed. It is shown, by comparison with the field measurements during the United Arab Emirates Unified Aerosol Experiment, that an assumption about specific particle shape is important for the extinction profile inversions. The authors indicate that this limitation of detection is a result of the relatively small sensitivity of this instrument in comparison to more sophisticated aerosol lidars. However, in many cases this does not play a significant role because globally only about 20% of the aerosol optical depth is above the boundary layer.

Markowicz, KM, Flatau PJ, Vogelmann AM, Quinn PK, Welton EJ.  2003.  Clear-sky infrared aerosol radiative forcing at the surface and the top of the atmosphere. Quarterly Journal of the Royal Meteorological Society. 129:2927-2947.   10.1256/qj.02.224   AbstractWebsite

We study the aerosol radiative forcing at infrared (IR) wavelengths using data from the Aerosol Characterization Experiment. ACE-Asia, cruise of the National Oceanic and Atmospheric Administration research vessel Ronald H. Brown. The analyses apply to the daytime periods of clear-sky conditions for the area within the immediate vicinity of the ship. An optical model is derived from chemical measurements, lidar profiles, and visible-extinction measurements, which are used to estimate the IR aerosol optical thickness and the single-scattering albedo. The IR model results are compared to detailed Fourier transform interferometer-based IR aerosol forcing estimates, pyrgeometer-based IR downward fluxes, and to observations of the direct aerosol solar forcing. This combined approach attests to the self-consistency of the optical model, and allows us to derive quantities such as the IR forcing at the top of the atmosphere (TOA) and the IR optical thickness. The mean IR aerosol optical thickness at 10 mum is 0.08 and the single-scattering albedo is 0.55. The modelled IR aerosol surface forcing reaches 10 W m(-2) during the cruise, which is a significant contribution compared to the total direct aerosol forcing. The surface IR aerosol radiative forcing is between 10 and 25% of the short-wave aerosol forcing. The IR aerosol forcing at the TOA can be up to 19% of the solar aerosol forcing. We show good agreement between TOA aerosol IR forcing derived from the model and from the CERES (Clouds and the Earth's Radiant Energy System) satellite data. Over the Sea of Japan, the average IR aerosol radiative forcing is 4.6 W m(-2) at the surface. and 1.5 W m(-2) at the TOA. The IR forcing efficiency at the TOA is a strong function of aerosol temperature (which is coupled to vertical structure) and changes between 10 and 18 W m(-2) (per IR optical depth unit), while the surface IR forcing efficiency varies between 37 and 55 W m(-2) (per IR optical depth unit).

Markowicz, KM, Flatau PJ, Quinn PK, Carrico CM, Flatau MK, Vogelmann AM, Bates D, Liu M, Rood MJ.  2003.  Influence of relative humidity on aerosol radiative forcing: An ACE-Asia experiment perspective. Journal of Geophysical Research-Atmospheres. 108   10.1029/2002jd003066   AbstractWebsite

We present direct radiometric observations of aerosol radiative forcing during the ACE-Asia experiment (March and April of 2001). The observational analysis is based on radiometer data obtained from the NOAA ship Ronald H. Brown, and shipboard measurements of the aerosol chemical and scattering properties are used to construct a model of the aerosol optical properties for use in radiative transfer calculations. The model is validated against the radiometric observations and is used to diagnose the aerosol and environmental factors that contribute to the observed forcings. The mean value of aerosol optical thickness observed during the ACE-Asia cruise over the Sea of Japan was 0.43 (+/-0.25) at 500 nm, while the single-scattering albedo was 0.95 (+/-0.03) at ambient relative humidity. We find a large correlation (r(2) = 0.69) between single-scattering albedo and relative humidity. Aerosols caused a mean decrease in the diurnally averaged solar radiation of 26.1 W m(-2) at the surface, while increasing the atmospheric solar absorption and top of atmosphere reflected solar radiation by 13.4 W m(-2) and 12.7 W m(-2), respectively. The mean surface aerosol forcing efficiency (forcing per unit optical depth) over the Sea of Japan was -60 W m(-2) and is influenced by high values of relative humidity. We show that decreasing the relative humidity to 55% enhances the aerosol forcing efficiency by as much as 6-10 W m(-2). This dependency on relative humidity has implications for comparisons of aerosol forcing efficiencies between different geographical locations.

Maslowska, A, Flatau PJ, Stephens GL.  1994.  On the Validity of the Anomalous Diffraction Theory to Light-Scattering by Cubes. Optics Communications. 107:35-40.   10.1016/0030-4018(94)90099-x   AbstractWebsite

The extinction and absorption efficiencies of a cube at light incidence normal to its four-fold symmetry axis are calculated using the anomalous diffraction theory (ADT). The results are compared with those based on the discrete dipole approximation (DDA). It is shown that for certain cases of the orientation of a cube relative to the direction of the incident light the extinction efficiency calculated using DDA and ADT do not agree. However, the ADT-based absorption efficiencies for the cases studied are dependent on a particle volume and exhibit smaller errors. Hence the validity of the ADT for cubes is not as good as for spheres.

Matthews, AJ, Baranowski DB, Heywood KJ, Flatau PJ, Schmidtko S.  2014.  The surface diurnal warm layer in the Indian Ocean during CINDY/DYNAMO. Journal of Climate. 27:9101-9122.   10.1175/jcli-d-14-00222.1   AbstractWebsite

A surface diurnal warm layer is diagnosed from Seaglider observations and develops on half of the days in the Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the Madden-Julian Oscillation (CINDY/DYNAMO) Indian Ocean experiment. The diurnal warm layer occurs on days of high solar radiation flux (>80 W m(-2)) and low wind speed (<6 ms(-1)) and preferentially in the inactive stage of the Madden-Julian oscillation. Its diurnal harmonic has an exponential vertical structure with a depth scale of 4-5m (dependent on chlorophyll concentration), consistent with forcing by absorption of solar radiation. The effective sea surface temperature (SST) anomaly due to the diurnal warm layer often reaches 0.8 degrees C in the afternoon, with a daily mean of 0.2 degrees C, rectifying the diurnal cycle onto longer time scales. This SST anomaly drives an anomalous flux of 4Wm(-2) that cools the ocean. Alternatively, in a climate model where this process is unresolved, this represents an erroneous flux that warms the ocean. A simple model predicts a diurnal warm layer to occur on 30%-50% of days across the tropical warm pool. On the remaining days, with low solar radiation and high wind speeds, a residual diurnal cycle is observed by the Seaglider, with a diurnal harmonic of temperature that decreases linearly with depth. As wind speed increases, this already weak temperature gradient decreases further, tending toward isothermal conditions.