Q Min - Academia.edu (original) (raw)

Papers by Q Min

The 1997/1998 El Nino induced changes in rainfall vertical structure in the East Pacific are stud... more The 1997/1998 El Nino induced changes in rainfall vertical structure in the East Pacific are studied by using Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and TRMM Microwave Imager (TMI) measurements during January-April of 1998, 1999, and 2000. NOAA OI daily SST and the nearest 6-hour ERA-40 reanalysis datasets are collocated with each PR FOV to provide the best estimation of associated SST and atmospheric states. We segregate PR precipitation profiles into convective, straitform, and warm rain regimes, and study the response of their vertical structures to the sea surface temperature. The precipitation top height (PTH) and precipitation top temperature (PTT) of convective rains change with SST at a rate of 0.51km/oC and -2.17 oC / oC, respectively. For stratiform rains, the associated rates are 0.59 km/ oC and -2.06 oC / oC, respectively. It implies that the storm system expanded vertically at a rate of about 6.4% per oC, which is close to the storm horizont...

ABSTRACT The latent heat (LH) released from tropical precipitation plays a critical role in drivi... more ABSTRACT The latent heat (LH) released from tropical precipitation plays a critical role in driving regional and global atmosphere circulation. However, the vertical distribution of LH is one of most difficult parameters to be measured and has a large uncertainty in both residual diagnostic products and satellite retrievals. Most of current satellite LH products use limited observational information of precipitation and cloud profiles and highly depend on cloud resolving model (CRM) simulations. Our novel approach, distinguishing from existing schemes, is directly using observable precipitation and cloud profiles in combination with phase change partition parameterization of various kinds from the CRM simulations to produce the latent heating profiles. This hybrid latent heat algorithm separately deals with the condensation-evaporation heating (LHc_e), the deposition-sublimation heating (LHd_s) and the freezing-melting heating (LHf_m) for convective rain, stratiform rain, and shallow warm rain. Each component is based on physical processes, such as nucleation and auto conversion, by combining observable precipitation and cloud profiles. Although the proposed algorithm utilizes microphysical parameterizations from a specific CRM, the general LH vertical structure is primarily determined by the precipitation and cloud profiles observable from cloud and precipitation radars available at ground sites or from satellite platforms, and less sensitive to the specific CRM. The self consistency tests of this algorithm show good agreements with the CRM simulated LH at different spatial and temporal scales, even at simultaneous and pixel level. The applications of this algorithm are expected to provide new information for understanding the heating budget in the atmosphere and its impacts on the atmosphere circulations at various spatial and temporal scales.

Cloud evolution is affected profoundly by aerosols and associated microphysical processes and by ... more Cloud evolution is affected profoundly by aerosols and associated microphysical processes and by cloud dynamics and thermodynamics. To isolate dynamic influences from microphysical impacts, we stratify warm cloud measurements of MODIS, AMSR, and CERES in four key ways: cloud precipitation regime, cloud top temperature (or height), cloud liquid water path, and aerosol number concentration. We found that correlations, which appear

It has been established that aerosols influence the Earth radiation balance through direct intera... more It has been established that aerosols influence the Earth radiation balance through direct interaction with solar radiation in what is called the Direct effect of aerosols. They also modify cloud microphysical, optical and radiative properties in what is termed the Indirect effect. Semi direct effect describes the offset that may occur as a result of local heating by absorbing aerosols. The Indirect effect is believed to be the more dominant effect of aerosols on climate and is estimated in to produce a global mean radiative forcing of as much as -2 Wm-2 (3rd IPCC assessment). This estimate, however, is highly uncertain; thus, considerable research effort continues to be directed towards better understanding of the aerosol indirect effect. The complex life cycles of aerosols as well as their regional nature make it necessary to develop more sites for aerosols and cloud studies. The investigation of the Indirect effect is being conducted with measurements collected at a newly develop...

Atmospheric Measurement Techniques Discussions, 2015

Getting an accurate cloud cover state is a challenging task. In the past, traditional two-dimensi... more Getting an accurate cloud cover state is a challenging task. In the past, traditional two-dimensional red-to-blue band methods have been widely used for cloud detection in total sky images. By analyzing the imaging principle of cameras, green channel has been selected to replace the 2-D red-to-blue band for total sky cloud detection. The brightness distribution in a total sky image is usually non-uniform, because of forward scattering and Mie scattering of aerosols, which results in increased detection errors in the circumsolar and near-horizon regions. This paper proposes an automatic cloud detection algorithm, "green channel background subtraction adaptive threshold" (GBSAT), which incorporates channel selection, background simulation, computation of solar mask and cloud mask, subtraction, adaptive threshold, and binarization. Several experimental cases show that the GBSAT algorithm is robust for all types of test total sky images and has more complete and accurate retri...

Atmospheric Chemistry and Physics Discussions, 2014

Long-term ground-based observations (2006 to 2010) of aerosol and cloud properties derived from p... more Long-term ground-based observations (2006 to 2010) of aerosol and cloud properties derived from passive radiometric sensors deployed at an atmospheric measurement field station in the Baltimore–Washington corridor operated by Howard University were used to examine aerosol indirect effect on cloud optical depth (COD), liquid water path (LWP), cloud droplets effective radius (Re) and cloud droplets number concentration (Nd). A higher frequency of clouds with large COD (> 20) and small Re (< 7 m) was found during summer of 2006 and 2007 along with higher frequency of abundant aerosol loading. The five-year data are screened for summer months only and are separated into clean and polluted cases based on aerosol particulate matter with aerodynamic diameter ≤ 2.5 m (PM2.5) value. Evidence of aerosol indirect effect is found where for po...

Journal of Quantitative Spectroscopy and Radiative Transfer, 2015

This is the second part on assessing the impacts of assimilating various distributions of sea-lev... more This is the second part on assessing the impacts of assimilating various distributions of sea-level pressure (SLP) on hurricane simulations, using the Weather and Research Forecast (WRF) three dimensional variational data assimilation system (3DVAR). One key purpose of this series of study is to explore the potential of using remotely sensed sea surface barometric data from O 2-band differential absorption radar system currently under development for server weather including hurricane forecasts. In this part II we further validate the conclusions of observational system simulation experiments (OSSEs)

Atmospheric Measurement Techniques, 2014

Various studies indicate that high-resolution oxygen A-band spectrum has the capability to retrie... more Various studies indicate that high-resolution oxygen A-band spectrum has the capability to retrieve the vertical profiles of aerosol and cloud properties. To improve the understanding of oxygen A-band inversions and utility, we developed a high-resolution oxygen A-band spectrometer (HABS), and deployed it at Howard University Beltsville site during the NASA Discover Air-Quality Field Campaign in July, 2011. By using a single telescope, the HABS instrument measures the direct solar and the zenith diffuse radiation subsequently. HABS exhibits excellent performance: stable spectral response ratio, high signal-to-noise ratio (SNR), high-spectrum resolution (0.016 nm), and high out-of-band rejection (10 −5). For the spectral retrievals of HABS measurements, a simulator is developed by combining a discrete ordinates radiative transfer code (DISORT) with the High Resolution Transmission (HITRAN) database HITRAN2008. The simulator uses a double-k approach to reduce the computational cost. The HABS-measured spectra are consistent with the related simulated spectra. For directbeam spectra, the discrepancies between measurements and simulations, indicated by confidence intervals (95 %) of relative difference, are (−0.06, 0.05) and (−0.08, 0.09) for solar zenith angles of 27 and 72 • , respectively. For zenith diffuse spectra, the related discrepancies between measurements and simulations are (−0.06, 0.05) and (−0.08, 0.07) for solar zenith angles of 27 and 72 • , respectively. The main discrepancies between measurements and simulations occur at or near the strong oxygen absorption line centers. They are mainly due to two kinds of causes: (1) measurement errors associated with the noise/spikes of HABS-measured spectra, as a result of combined effects of weak signal, low SNR, and errors in wavelength registration; (2) modeling errors in the simulation, including the error of model parameters setting (e.g., oxygen absorption line parameters, vertical profiles of temperature and pressure) and the lack of treatment of the rotational Raman scattering. The high-resolution oxygen A-band measurements from HABS can constrain the active radar retrievals for more accurate cloud optical properties (e.g., cloud optical depth, effective radius), particularly for multi-layer clouds and for mixed-phase clouds.

Atmospheric Chemistry and Physics Discussions, 2010

Here we report the results of three parallel efforts: the recal - 0.3%. Likewise, Joe Michalsky w... more Here we report the results of three parallel efforts: the recal - 0.3%. Likewise, Joe Michalsky went to the SGP site with a ibration and reanalysis of pyrano-metric data from Souther n recently calibrated Eppley Normal Incidence Pyrheliometer Great Plains (SGP) to improve its accuracy, use of th e (NIP) and an Eppley Precision Spectral Pyranometer (PSP). multifilter rotating shadowband radiometer (MFRSR) data to derive cloud optical depths and then tests of radiative transfe r The Baseline Surface Radiation Network (BSRN) and Solar models to predict shortwave irradiance under cloudy skies , and Infrared Observing System (SIROS) complements of and operational results for the Rotating Shadowband Spectro - shortwave instruments (those permanently operating at th e radiometer (RSS) operated at SGP during the H O intensiv e SGP) include pyrheliometers, unshaded pyranometers, and 2 observation period (IOP) compared to MODTRAN-3.5. shaded pyranometers. Thus, during these calibratio n

Journal of Geophysical Research: Atmospheres, 2008

Journal of Geophysical Research, 2010

Photon path length distribution is sensitive to 3-D cloud structures. A detection method for mult... more Photon path length distribution is sensitive to 3-D cloud structures. A detection method for multilayer clouds has been developed, by utilizing the information of photon path length distribution. The photon path length method estimates photon path length information from the low level, single-layer cloud structure that can be accurately observed by a millimeter-wave cloud radar (MMCR) combined with a micropulse lidar (MPL). As multiple scattering within the cloud layers and between layers would substantially enhance the photon path length, the multilayer clouds can be diagnosed by evaluating the estimated photon path information against observed photon path length information from a co-located rotating shadowband spectrometer (RSS). The measurements of MMCR-MPL and RSS at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site have been processed for the year 2000. Cases studies illustrate the consistency between MMCR-MPL detection and the photon path length method under most conditions. However, the photon path length method detected some multilayer clouds that were classified by the MMCR-MPL as single-layer clouds. From 1 year statistics at the ARM SGP site, about 27.7% of single-layer clouds detected by the MMCR-MPL with solar zenith angle less than 70°and optical depth greater than 10 could be multilayer clouds. It suggests that a substantial portion of single-layer clouds detected by the MMCR-MPL could also be influenced by some "missed" clouds or by the 3-D effects of clouds.

IEEE Transactions on Geoscience and Remote Sensing, 2008

Bulletin of the American Meteorological Society, 2007

Atmospheric Chemistry and Physics, 2012

Utilizing the unique characteristics of the cloud over the Southeast Pacific (SEP) off the coast ... more Utilizing the unique characteristics of the cloud over the Southeast Pacific (SEP) off the coast of Chile during the VOCALS field campaign, we compared satellite remote sensing of cloud microphysical properties against insitu data from multi-aircraft observations, and studied the extent to which these retrieved properties are sufficiently constrained and consistent to reliably quantify the influence of aerosol loading on cloud droplet sizes. After constraining the spatial-temporal coincidence between satellite retrievals and in-situ measurements, we selected 17 non-drizzle comparison pairs. For these cases the mean aircraft profiling times were within one hour of Terra overpasses at both projected and un-projected (actual) aircraft positions for two different averaging domains of 5 km and 25 km. Retrieved quantities that were averaged over a larger domain of 25 km compared better statistically with in-situ observations than averages over a smaller domain of 5 km. Comparison at projected aircraft positions was slightly better than un-projected aircraft positions for some parameters. Overall, both MODISretrieved effective radius and LWP were larger but highly correlated with the in-situ measured effective radius and LWP, e.g., for averaging domains of 5 km, the biases are up to 1.75 µm and 0.02 mm whilst the correlation coefficients are about 0.87 and 0.85, respectively. The observed effective radius difference between the two decreased with increasing cloud drop number concentration (CDNC), and increased with increasing cloud geometrical thickness. Compared to the absolute effective radius difference, the correlations between the relative effective radius difference and CDNC or cloud geometric thickness are weaker. For averaging domains of 5 km and 25 km, the correlation coefficients between MODIS-retrieved and in-situ measured CDNC are 0.91 and 0.93 with fitting slopes of 1.23 and 1.27, respectively. If the cloud adiabaticity is taken into account, better agreements are achieved for both averaging domains (the fitting slopes are 1.04 and 1.07, respectively). Our comparison and sensitivity analysis of simulated retrievals demonstrate that both cloud geometrical thickness and cloud adiabaticity are important factors in satellite retrievals of effective radius and cloud drop number concentration. The large variabilities in cloud geometrical thickness and adiabaticity, the dependencies of cloud microphysical properties on both quantities (as demonstrated in our sensitivity study of simulated retrievals), and the inability to accurately account for either of them in retrievals lead to some uncertainties and biases in satellite retrieved cloud effective radius, cloud liquid water path, and cloud drop number concentration. However, strong correlations between satellite retrievals and in-situ measurements suggest that satellite retrievals of cloud effective radius, cloud liquid water path, and cloud drop number concentration can be used to investigate aerosol indirect effects qualitatively.

Atmospheric Chemistry and Physics, 2010

In addition to microphysical changes in clouds, changes in nucleation processes of ice cloud due ... more In addition to microphysical changes in clouds, changes in nucleation processes of ice cloud due to aerosols would result in substantial changes in cloud top distribution as mildly supercooled clouds are glaciated through heterogonous nucleation processes. Measurements from multiple sensors on multiple observing platforms over the Atlantic Ocean show that the cloud effective temperature increases with mineral dust loading with a slope of +3.06 • C per unit AOD. The macrophysical changes in ice cloud top distributions as a consequence of mineral dust-cloud interaction exert a strong cooling effect (up to 16 w m −2) of thermal infrared radiation on cloud systems. Induced changes of ice particle size by mineral dusts influence cloud emissivity and play a minor role in modulating the outgoing longwave radiation for optically thin ice clouds. Such a strong cooling forcing of thermal infrared radiation would have significant impacts on cloud systems and subsequently on climate.

Atmospheric Chemistry and Physics, 2011

A spatial-temporal analysis has been conducted using satellite observed distributions of rain fre... more A spatial-temporal analysis has been conducted using satellite observed distributions of rain frequency, NO 2 concentration and aerosol, with focus on the spring season in East Asia. As NO 2 is a key precursor of secondary aerosols, especially in urban areas, an increase of NO 2 emission is generally accompanied by an increase of fine aerosol particles. Comparison between trends in rain frequency and in precipitation amount shows that the changes in precipitation are more due to changes in precipitation occurrence than in precipitation amount. The overall feature emerged from the region-by-region analyses is that there is an inverse relationship between the rain frequency and the pollution and associated aerosols at continental scale in spring. The change in rain frequency is associated with changes in pollution-produced aerosols and long-range transport mineral dust. The inverse relationship at large temporal and spatial scales illustrates potential climatological consequence of changed pollution and aerosols on precipitation. Due to relatively short duration of observation and the potential uncertainty and bias associated with satellite measurements, more robust longer-term statistical study at various temporal and spatial scales and detailed modeling investigation are warranted to understand the physical causality of observed relationship between the rain frequency and the pollution and associated aerosols.