Baltimore, MD, United States
Baltimore, MD, United States

Time filter

Source Type

Zhang Z.,University of Maryland Baltimore County | Zhang Z.,Joint Center for Earth Systems Technology | Zhang Z.,NASA | Ackerman A.S.,NASA | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2012

This study investigates effects of drizzle and cloud horizontal inhomogeneity on cloud effective radius (re) retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS). In order to identify the relative importance of various factors, we developed a MODIS cloud property retrieval simulator based on the combination of large-eddy simulations (LES) and radiative transfer computations. The case studies based on synthetic LES cloud fields indicate that at high spatial resolution (∼100 m) 3-D radiative transfer effects, such as illumination and shadowing, can induce significant differences between retrievals of re based on reflectance at 2.1 m (re,2.1) and 3.7 m (re,3.7). It is also found that 3-D effects tend to have stronger impact on re,2.1 than r e,3.7, leading to positive difference between the two (r e,3.7-2.1) from illumination and negative re,3.7-2.1 from shadowing. The cancellation of opposing 3-D effects leads to overall reasonable agreement between re,2.1 and re,3.7 at high spatial resolution as far as domain averages are concerned. At resolutions similar to MODIS, however, re,2.1 is systematically larger than r e,3.7 when averaged over the LES domain, with the difference exhibiting a threshold-like dependence on both re,2.1 and an index of the sub-pixel variability in reflectance (Hσ), consistent with MODIS observations. In the LES cases studied, drizzle does not strongly impact re retrievals at either wavelength. It is also found that opposing 3-D radiative transfer effects partly cancel each other when cloud reflectance is aggregated from high spatial resolution to MODIS resolution, resulting in a weaker net impact of 3-D radiative effects on re retrievals. The large difference at MODIS resolution between re,3.7 and r e,2.1 for highly inhomogeneous pixels with Hσ > 0.4 can be largely attributed to what we refer to as the "plane-parallel re bias," which is attributable to the impact of sub-pixel level horizontal variability of cloud optical thickness on re retrievals and is greater for re,2.1 than re,3.7. These results suggest that there are substantial uncertainties attributable to 3-D radiative effects and plane-parallel re bias in the MODIS re,2.1 retrievals for pixels with strong sub-pixel scale variability, and the H σ index can be used to identify these uncertainties. © 2012 American Geophysical Union. All Rights Reserved.

Finlay C.C.,ETH Zurich | Maus S.,University of Colorado | Beggan C.D.,British Geological Survey | Bondar T.N.,RAS Institute of Radio Engineering and Electronics | And 31 more authors.
Geophysical Journal International | Year: 2010

The eleventh generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2009 by the International Association of Geomagnetism and Aeronomy Working Group V-MOD. It updates the previous IGRF generation with a definitive main field model for epoch 2005.0, a main field model for epoch 2010.0, and a linear predictive secular variation model for 2010.0-2015.0. In this note the equations defining the IGRF model are provided along with the spherical harmonic coefficients for the eleventh generation. Maps of the magnetic declination, inclination and total intensity for epoch 2010.0 and their predicted rates of change for 2010.0-2015.0 are presented. The recent evolution of the South Atlantic Anomaly and magnetic pole positions are also examined. © 2010 The Authors Geophysical Journal International © 2010 RAS.

Sawamura P.,University of Maryland Baltimore County | Vernier J.P.,NASA | Barnes J.E.,National Oceanic and Atmospheric Administration | Berkoff T.A.,Joint Center for Earth Systems Technology | And 16 more authors.
Environmental Research Letters | Year: 2012

Nabro volcano (13.37°N, 41.70°E) in Eritrea erupted on 13 June 2011 generating a layer of sulfate aerosols that persisted in the stratosphere for months. For the first time we report on ground-based lidar observations of the same event from every continent in the Northern Hemisphere, taking advantage of the synergy between global lidar networks such as EARLINET, MPLNET and NDACC with independent lidar groups and satellite CALIPSO to track the evolution of the stratospheric aerosol layer in various parts of the globe. The globally averaged aerosol optical depth (AOD) due to the stratospheric volcanic aerosol layers was of the order of 0.018±0.009 at 532nm, ranging from 0.003 to 0.04. Compared to the total column AOD from the available collocated AERONET stations, the stratospheric contribution varied from 2% to 23% at 532nm. © 2012 IOP Publishing Ltd.

Wehner B.,Leibniz Institute for Tropospheric Research | Werner F.,Leipzig Institute for Meteorology | Werner F.,Joint Center for Earth Systems Technology | Ditas F.,Leibniz Institute for Tropospheric Research | And 4 more authors.
Atmospheric Chemistry and Physics | Year: 2015

During the CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over Barbados) campaign, the interaction between aerosol particles and cloud microphysical properties was investigated in detail, which also includes the influence of clouds on the aerosol formation. During two intensive campaigns in 2010 and 2011, helicopter-borne measurement flights were performed to investigate the thermodynamic, turbulent, microphysical, and radiative properties of trade-wind cumuli over Barbados. During these flights, 91 cases with increased aerosol particle number concentrations near clouds were detected. The majority of these cases are also correlated with enhanced irradiance in the ultraviolet (UV) spectral wavelength range. This enhancement reaches values up to a factor of 3.3 greater compared to background values. Thus, cloud boundaries provide a perfect environment for the production of precursor gases for new particle formation. Another feature of cloud edges is an increased turbulence, which may also enhance nucleation and particle growth. The observed events have a mean length of 100 m, corresponding to a lifetime of less than 300 s. This implies that particles with diameters of at least 7 nm grew several nanometers per minute, which corresponds to the upper end of values in the literature (Kulmala et al., 2004). Such high values cannot be explained by sulfuric acid alone; thus extremely low volatility organic compounds (ELVOCs) are probably involved here. © 2015 Author(s).

Liao L.,Morgan State University | Meneghini R.,NASA | Tokay A.,University of Maryland Baltimore County | Tokay A.,Joint Center for Earth Systems Technology | Bliven L.F.,NASA
Journal of Applied Meteorology and Climatology | Year: 2016

The focus of this study is on the estimation of snow microphysical properties and the associated bulk parameters such as snow water content and water equivalent snowfall rate for Ku- and Ka-band dual-frequency radar. This is done by exploring a suitable scattering model and the proper particle size distribution (PSD) assumption that accurately represent, in the electromagnetic domain, the micro-/macrophysical properties of snow. The scattering databases computed from simulated aggregates for small-to-moderate particle sizes are combined with a simple scattering model for large particle sizes to characterize snow-scattering properties over the full range of particle sizes. With use of the single-scattering results, the snow retrieval lookup tables can be formed in a way that directly links the Ku- and Ka-band radar reflectivities to snow water content and equivalent snowfall rate without use of the derived PSD parameters. A sensitivity study of the retrieval results to the PSD and scattering models is performed to better understand the dual-wavelength retrieval uncertainties. To aid in the development of the Ku- and Ka-band dual-wavelength radar technique and to further evaluate its performance, self-consistency tests are conducted using measurements of the snow PSD and fall velocity acquired from the Snow Video Imager/Particle Image Probe (SVI/PIP) during the winter of 2014 at the NASA Wallops Flight Facility site in Wallops Island, Virginia. © 2016 American Meteorological Society.

Sullivan J.T.,University of Maryland Baltimore County | Sullivan J.T.,Joint Center for Earth Systems Technology | Sullivan J.T.,NASA | Sullivan J.T.,Oak Ridge Associated Universities | And 7 more authors.
Journal of Atmospheric and Oceanic Technology | Year: 2015

During a 2-week period in May 2014, the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center Tropospheric Ozone Differential Absorption Lidar (GSFC TROPOZ DIAL) was situated near the NASA Langley Research Center (LaRC) Mobile Ozone Lidar (LMOL) and made simultaneous measurements for a continuous 15-h observation period in which six separate ozonesondes were launched to provide reference ozone profiles. Although each of these campaign-ready lidars has very different transmitter and receiver components, they produced very similar ozone profiles, which were mostly within 10% of each other and the ozonesondes. The observed column averages as compared to the ozonesondes also agree well and are within 8% of each other. A robust uncertainty analysis was performed, and the results indicate that there is no statistically significant systematic bias between the TROPOZ and LMOL instruments. With the extended measurements and ozonesonde launches, this intercomparison has yielded an in-depth evaluation of the precision and accuracy of the two new lidars. This intercomparison is also the first (to the best of the authors' knowledge) reported measurement intercomparison of two ground-based tropospheric ozone lidar systems within the United States. © 2015 American Meteorological Society.

Georgieva E.M.,Joint Center for Earth Systems Technology | Huang W.,Science Systems And Applications Inc. | Heaps W.S.,NASA
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

A portable remote sensing system for precision column measurements of methane has been developed, built and tested at NASA GSFC. The sensor covers the spectral range from 1.636 μm to 1.646 μm, employs an air-gapped Fabry-Perot filter and a CCD camera and has a potential to operate from a variety of platforms. The detector is an XS-1.7-320 camera unit from Xenics Infrared solutions 1which combines an uncooled InGaAs detector array working up to 1.7 μm. Custom software was developed in addition to the graphical user basic interface X-Control provided by the company to help save and process the data. The technique and setup can be used to measure other trace gases in the atmosphere with minimal changes of the etalon and the prefilter. In this paper we describe the calibration of the system using several different approaches. © 2012 IEEE.

Miller D.J.,University of Maryland Baltimore County | Zhang Z.,University of Maryland Baltimore County | Zhang Z.,Joint Center for Earth Systems Technology | Ackerman A.S.,NASA | And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2016

Passive optical retrievals of cloud liquid water path (LWP), like those implemented for Moderate Resolution Imaging Spectroradiometer (MODIS), rely on cloud vertical profile assumptions to relate optical thickness (τ) and effective radius (re) retrievals to LWP. These techniques typically assume that shallow clouds are vertically homogeneous; however, an adiabatic cloud model is plausibly more realistic for shallow marine boundary layer cloud regimes. In this study a satellite retrieval simulator is used to perform MODIS-like satellite retrievals, which in turn are compared directly to the large-eddy simulation (LES) output. This satellite simulator creates a framework for rigorous quantification of the impact that vertical profile features have on LWP retrievals, and it accomplishes this while also avoiding sources of bias present in previous observational studies. The cloud vertical profiles from the LES are often more complex than either of the two standard assumptions, and the favored assumption was found to be sensitive to cloud regime (cumuliform/stratiform). Confirming previous studies, drizzle and cloud top entrainment of dry air are identified as physical features that bias LWP retrievals away from adiabatic and toward homogeneous assumptions. The mean bias induced by drizzle-influenced profiles was shown to be on the order of 5-10 g/m2. In contrast, the influence of cloud top entrainment was found to be smaller by about a factor of 2. A theoretical framework is developed to explain variability in LWP retrievals by introducing modifications to the adiabatic re profile. In addition to analyzing bispectral retrievals, we also compare results with the vertical profile sensitivity of passive polarimetric retrieval techniques. ©2016. American Geophysical Union. All Rights Reserved.

Georgieva E.M.,Joint Center for Earth Systems Technology | Heaps W.S.,NASA
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2011

Progress on the development of a differential radiometer based upon the Fabry-Perot interferometer (FPI) for methane (CH4) and carbon dioxide (CO 2) detection in the atmosphere is presented. Carbon dioxide and methane measurements are becoming increasingly important as a component of NASA's programs to understand the global carbon cycle and quantify the threat of global warming. Methane is the third most important greenhouse gas in the Earth's radiation budget (after water vapor and carbon dioxide) and the second most important anthropogenic contributor to global warming. The importance of global warming and air quality to society caused the National Research Council to recommend that NASA develop the following three missions1,2 ASCENDS (Active Sensing of CO2 Emissions over Nights, Days, and Seasons), GEOCAPE (Geostationary Coastal and Air Pollution Events), and GACM (Global Atmosphere Composition Mission). The importance of CO2 and methane study is reflected in the successful operation of the Japanese Greenhouse gases Observing Satellite (GOSAT) monitoring those trace gases globally from orbit.3 © 2011 IEEE.

Kuang W.,NASA | Wei Z.,Joint Center for Earth Systems Technology | Holme R.,University of Liverpool | Tangborn A.,Joint Center for Earth Systems Technology
Earth, Planets and Space | Year: 2010

Data assimilation has been used in meteorology and oceanography to combine dynamical models and observations to predict changes in state variables. Along similar lines of development, we have created a geomagnetic data assimilation system, MoSST-DAS, which includes a numerical geodynamo model, a suite of geomagnetic and paleomagnetic field models dating back to 5000 BCE, and a data assimilation component using a sequential assimilation algorithm. To reduce systematic errors arising from the geodynamo model, a prediction-correction iterative algorithm is applied for more accurate forecasts. This system and the new algorithm are tested with 7-year geomagnetic forecasts. The results are compared independently with CHAOS and IGRF field models, and they agree very well. Utilizing the geomagnetic field models up to 2009, we provide our prediction of 5year mean secular variation (SV) for the period 2010-2015 up to degree L = 8. Our prediction is submitted to IGRF-11 as a candidate SV model. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

Loading Joint Center for Earth Systems Technology collaborators
Loading Joint Center for Earth Systems Technology collaborators