The aerosol-cloud interaction is a complex and critical process in assessing the climate radiative effects of aerosol and
cloud. Lidar can simultaneously measure the range-resolved distribution of aerosol-cloud with the high spatial-temporal
resolution, and hence provides the opportunity to explore the cloud-aerosol optical properties and their interaction. Their
interactions have been indicated by the significant variation of optical properties and droplet size of aerosol and cloud at
the cloud vicinity or edges. But due to dramatic non-linear or irregular variation of lidar returns by the cloud, the
evaluation of lidar algorithm deriving cloud extinction coefficient becomes quite important especially at the edges
because the common algorithms may result in the artificial influence on the retrievals of cloud extinction and extinctionto-
backscatter ratio (e.g. lidar ratio or S-ratio). In particular, the relationships of water cloud optical properties with the
droplet size are simulated which include lidar ratio, color ratio and extinction ratio are used and general trends with
measurements are demonstrated. To obtain color ratios (355/1064), a good calibration procedure for the 1064nm
channel is required and we show that calibration errors using low water drop clouds allow absolute calibration < 10%.
Preliminary results seem to indicate that small pre-nucleated droplets form at the aerosol - cloud boundary which is
consistent with aerosol uptake into clouds. In addition, we also explore the increase in aerosol lidar-ratio below cloud
indicative of hygroscopic growth.
In this paper, the simulations of the Weather Research and Forecast (WRF) and Community Multiscale Air Quality
(CMAQ) Models applied to the New York City (NYC) area are assessed with the aid of vertical profiling and column
integrated remote sensing measurements. First, we find that when turbulent mixing processes are dominant, the WRFderived
planetary boundary layer (PBL) height exhibits a strong linear correlation (R>0.85) with lidar-derived PBL
height. In these comparisons, we estimate the PBL height from the lidar measurements using a Wavelet Covariance
Transform (WCT) approach that is modified to better isolate the convective layer from the residual layer (RL).
Furthermore, the WRF-Lidar PBL height comparisons are made using different PBL parameterization schemes,
including the Asymmetric Convective Model-version2 (ACM2) and the Modified Blackadar (BLK) scheme (which are
both runs using hindcast data), as well as the Mellor-Yamada-Janjic (MYJ) scheme run in forecast mode. Our findings
show that the correlations for these runs are high (>0.8), but the hindcast runs exhibit smaller overall dispersion (≈0.1)
than the forecast runs. We also apply continuous 24-hour/7-day vertical ceilometer measurements to assess WRFCMAQ
model forecasts of surface PM2.5 (particulate matter has aerodynamic diameter <2.5μm). Strong overestimations
in the surface PM2.5 mass that are observed in the summer prior to sunrise are particularly shown to be strongly
connected to underestimations of the PBL height and less to enhanced emissions. This interpretation is consistent with
observations that TEOM (Tapered Element Oscillating MicroBalance) PM2.5 measurements are better correlated to pathintegrated
CMAQ PM2.5 than the near-surface measurements during these periods.
The planetary boundary layer (PBL) heights are derived from the CALIOP/CALIPSO level-1B attenuated backscatter
profile using the wavelet transform technique. The results are compared to those by the radiosonde and ground-based
lidar coincident measurements. The comparison generally indicates the good agreement and the correlation coefficient is
greater than 0.7. In addition, we found the good consistence between the CALIOP-derived PBL height and the selected
aerosol-layer-top of CALIPSO level-2 aerosol-layer products (5-km average). Finally, the spatial distribution of PBL
heights and their seasonal differences are initially illustrated over the US continent.
Measurements of low-altitude cloud and its interaction with aerosol are analyzed with a multiple-wavelength elastic-
Raman scattering lidar. Using the numerical experiment approach, we first evaluate the retrieval accuracy of cloud
extinction from the Raman-lidar algorithms, in particular at the cloud edges. For the low-level water-phase cloud,
the simulation also shows the dramatic variation of lidar-ratio, color-ratio and extinction-ratio with the small
droplets and their correlation. Then, the measurement examples by CCNY elastic-Raman lidar illustrate that the
small droplets probably appear at the cloud edges, which might imply the new particle formation or the cloudaerosol
interaction.
The need to characterize in a robust way Planetary Boundary Layer (PBL) heights is crucial as in air quality forecast and
transport models. In particular, incorrect determination of PBL heights can severely distort the surface air quality
predictions such as PM2.5. Local properties and morphological features can influence PBL dynamics through local
circulation phenomena such as the sea-breeze development as well as influences from the Urban Heat Island Canopy
resulting in multiple layers that need to be resolved. In this paper, based on a combination of wavelet and image
processing methods, we develop methods to quantify multilayer PBL's and assess their dynamics with meteorological
measurements including temperature, wind and humidity profiles. In particular, meteorologically based PBL heights
based on both the Potential Temperature Gradient and Richardson Number are compared against both lidar and
ceilometer measurements. It is shown that in general, the Potential Temperature Gradient method is better correlated to
the PBL dynamics. Meanwhile, the Hysplit model provides sounding data which can be used for comparison between
actual sounding and lidar measurements. On the other hand, when strong atmospheric instability is present or layering
develops, the comparison between different methods can provide information about the PBL internal structure. Further
comparisons with air quality models such as MM5 are also made and illustrate the difficulty in these models properly
predicting the PBL dynamics seen in urban areas.
Indentifying and quantifying ambient aerosols are important for air-quality applications. Unlike trace gases where
chemical spectral signatures are sharp and well defined, aerosol spectral signatures are broader and highly overlapping.
Therefore separation of aerosols into different size classes requires very broad spectral coverage from the visible (VIS)
to mid-infrared (MIR). In this paper, we investigate the feasibility in using a VIS (0.65μm) diode laser combined with a
suitable pulsed high power Quantum Cascade Laser (4.6μm) to obtain backscatter measurements that can be used to
isolate fine and coarse mode aerosol fractions. Based on realistic source characteristics, we study the information content
in the spectral extinction using different combinations of extinction measurements using Least Squares Minimization
applied to a wide range of aerosol multimode mixtures obtained using realistic models obtained from the Optical
Properties of Aerosol and Clouds (OPAC) model. This model is especially convenient since the optical spectral
extinction and backscatter spectra are evaluated over a wide wavelength range from 250nm to 40μm. In particular, we
find that with the latest QCL systems, it is possible to achieve signal to noise ratio (SNR) values ~10 with suitable
temporal and spatial averaging for aerosol layers ~1.5km making it suitable for PBL layer studies.
Smoke and dust aerosol plumes are observed by the ground-based multi-wavelength elastic-Raman lidar, sunphotometer
and space-borne lidar CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization). Lidar-derived multi-wavelength
aerosol extinction profiles and column lidar ratios are constrained by the independently measured optical
depths. The aloft smoke plume layers from Idaho/Montana forest fires were measured at 2~8 km altitude by the ground
lidar on Aug. 14~15, 2007. High aerosol optical depths (AOD) are shown with the value of 0.6~0.8 at wavelength 500
nm and Angstrom exponent of 1.8. The CALIOP observations generally show consistent plume height distribution with
the ground lidar, but partly misclassify these smoke plumes as clouds. The forest fire sources and intra-continental
smoke transport are clearly illustrated by CALIOP and MODIS satellite imageries. For the moderate dust-like plumes on
April 18, 2008, they were observed at the altitude of 2~6 km. Aerosol optical depths vary from 0.2 to 0.4 at wavelength
500 nm with Angstrom exponent <1.0 in the plume-layer. Ground-lidar and CALIOP retrievals show the good
agreement in dust-like layer heights, extinction profiles and aerosol species classification.
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