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At least 919 records · Page 51

Incorporation of surface albedo-temperature feedback in a one-dimensional radiative-connective climate model

The feedback between ice snow albedo and temperature is included in a one dimensional radiative convective climate model. The effect of this feedback on sensitivity to changes in solar constant is studied for the current values of the solar constant and cloud characteristics. The ice snow albedo feedback amplifies global climate sensitivity by 33% and 50%, respectively, for assumptions of constant cloud altitude and constant cloud temperature.

Wang, W. C.↗

A cloud model-radiative model combination for determining microwave TB-rain rate relations

The development of a cloud model-radiative transfer model combination for computing average brightness temperature, T(B), is discussed. The cloud model and radiative transfer model used in this study are described. The relations between rain rate, cloud and rain water, cloud and precipitation ice, and upwelling radiance are investigated. The effects of the rain rate relations on T(B) under different climatological conditions are examined. The model-derived T(B) results are compared to the 92 and 183 GHz aircraft observations of Hakkarinen and Adler (1984, 1986) and the radar-estimated rain rate of Hakkarinen and Adler (1986); good correlation between the data is detected.

Szejwach, Gerard↗

Further studies of the circulation of the Venus atmosphere

Previous calculations of zonally averaged temperature, circulation, and eddy source requirements for the Venus atmosphere are extended to include the region from the surface to 95 km, using a Curtis-matrix method for the radiation calculation. The cloud top circulation is not significantly changed from previous calculations based on a radiative-relaxation method, but large differences occur in the lower atmosphere. The physical and dynamical states of the atmospheric regions above and below the cloud base are effectively independent and are equally important for accounting for the 4-day circulation at the cloud tops. Above the cloud base, the circulation is effectively inviscid, and the eddy source requirements at the low latitudes are consistent with the mean-flow forcing by the semidiurnal tide. The circulation below the clouds is important compared to viscous dissipation above the lowest scale height.

Hou, Arthur Y.↗

Studies of Ice Nucleating Aerosol Particles in Arctic Cloud Systems

The focus of this research is to improve the understanding of ice nucleating aerosol particles (IN) and the role they play in ice formation in Arctic clouds. IN are important for global climate issues in a variety of ways. The primary effect is their role in determining the phase (liquid or solid) of cloud particles. The microscale impact is on cloud particle size, growth rate, shape, fall speed, concentration, radiative properties, and scavenging of gases and aerosols. On a larger scale, ice formation affects the development of precipitation (rate, amount, type, and distribution), latent heat release (rate and altitude), ambient humidity, the persistence of clouds, and cloud albedo. The overall goals of our FIRE 3 research are to characterize the concentrations and variability of Arctic IN during the winter-spring transition, to compare IN measurements with ice concentrations in Arctic clouds, and to examine selected IN samples for particle morphology and chemical there are distinguishable chemical signatures. The results can be combined with other measurements of aerosols, gaseous species, and cloud characteristics in order to understand the processes that determine the phase and concentration of cloud particles.

Rogers, David C.↗

Observed Differences in Spectral Microphysical Retrievals from MODIS

The microphysical structure of clouds is of fundamental importance for understanding a variety of cloud radiation and physical processes. With the advent of MODIS (Moderate Resolution Imaging Spectroradiometer) on the NASA EOS Terra and Aqua platforms, simultaneous global/daily 1km retrievals of cloud effective particle size are available using the heritage 3.7 an band from AVHRR as well as the 1.6 and 2.1 m shortwave IR bands. The MODIS cloud product (MOD06/MYD06 for MODIS Terra and Aqua, respectively) provides separate effective radii results using each of these spectral bands. It has been found that significant differences can occur between the three size retrievals, mainly for liquid water marine boundary layer clouds and especially in broken (low cloud fraction) regimes. In particular, for such regimes, effective radii derived from the MODIS 2.1 lim band can be substantially larger than retrievals from the Heritage 3.7 lam band. In this paper, we present global and regional results of the differences, including correlations, view angle dependencies, and algorithm sensitivities for the existing MODIS Collection 5 product.

Platnick, Steven E.↗

Using AI/ML to Address Satellite Cloud Remote Sensing Challenges

Various AI/ML tools, employed within the Clouds and the Earth's Radiant Energy System (CERES) Satellite Cloud and Radiation Property retrieval System (SatCORPS) project, are being used to mitigate satellite radiance artifacts and thereby yield more accurate cloud and radiation data products. Neural network and K-nearest neighbor approaches have been developed that enable us to better address common passive satellite remote sensing challenges, such as corrupted imagery, day/night cloud property discontinuities, solar terminator artifacts, inadequate knowledge of the land surface emission temperature (i.e., skin temperature), and poor assumptions about vertical cloud structure, that have otherwise proven difficult to solve using more conventional methods. Fixing these problems promotes a more consistent Earth radiation budget record. These efforts demonstrate effective use of AI/ML architecture to exploit complex, multivariate predictor relationships and produce usable output at satellite spatial and temporal resolutions that would otherwise be ignored or have large biases.

Benjamin Scarino↗

Time-dependent Photoionization Modeling of Warm Absorbers: High-resolution Spectra and Response to Flaring Light Curves

Time-dependent photoionization modeling of warm absorber (WA) outflows in active galactic nuclei can play an important role in understanding the interaction between WAs and the central black hole. The WA may be out of the equilibrium state because of the variable nature of the central continuum. In this paper, with the help of time dependent photoionization modeling, we study how the WA gas properties change with time and how it reacts to changing radiation fields. Incorporating a flaring incident light curve, we investigate the behavior of WAs using a photoionization code that simultaneously and consistently solves the time-dependent equations of level population, heating and cooling, and radiative transfer. We simulate the physical processes in the gas clouds, such as ionization, recombination, heating, cooling, and the transfer of ionizing radiation through the cloud and present high-resolution time-resolved absorption spectra. We demonstrate that time-dependent radiative transfer is important and the calculations that omit this effect quantitatively and systematically underestimate the absorption. Time-dependent photoionization models provide crucial insights into the characteristics of WAs and can be used to constrain their density and spatial distribution.

Astrophysicists↗

Time-Dependent Photoionization Modeling of Warm Absorbers: High-Resolution Spectra and Response to Flaring Light Curves

Time-dependent photoionization modeling of warm absorber (WA) outflows in active galactic nuclei can play an important role in understanding the interaction between WAs and the central black hole. The WA may be out of the equilibrium state because of the variable nature of the central continuum. In this paper, with the help of time dependent photoionization modeling, we study how the WA gas properties change with time and how it reacts to changing radiation fields. Incorporating a flaring incident light curve, we investigate the behavior of WAs using a photoionization code that simultaneously and consistently solves the time-dependent equations of level population, heating and cooling, and radiative transfer. We simulate the physical processes in the gas clouds, such as ionization, recombination, heating, cooling, and the transfer of ionizing radiation through the cloud and present high-resolution time-resolved absorption spectra. We demonstrate that time-dependent radiative transfer is important and the calculations that omit this effect quantitatively and systematically underestimate the absorption. Time-dependent photoionization models provide crucial insights into the characteristics of WAs and can be used to constrain their density and spatial distribution.

Dev R. Sadaula↗

Spectral variation of scattering and absorption by cirrus

The impact of cirrus clouds on the radiative budget of the earth depends on the microphysics and scattering properties of the clouds. Cirrus clouds have been especially difficult to observe because of their high altitude and complex tenuous structure. Observations by Abakumova et. al. (1991) show that the near infrared wavelengths are more sensitive to the cirrus cloud properties than the shorter ultraviolet wavelengths. Anikin (1991) was able to show that collimated spectral measurements can be used to determine an effective particle size of the cirrus clouds. Anikin (1991) also showed that the effect of scattering through cloud causes the apparent optical depth of a 10 degrees field of view pyrheliometer to be roughly half the actual optical depth. Stackhouse and Stephens (1991) have shown that the existence of small ice crystals do dramatically affect the radiative properties of the cirrus, though observations taken during the 1986 FIRE were not totally explained by their presence.

Hein, Paul F.↗

Molecular evolution of contracting clouds - Basic methods and initial results

The relationship between the dynamics of the interstellar gas and the thermal and chemical effects associated with interstellar molecules and dust is investigated. The evolution of a rather massive isolated initially diffuse cloud under self-gravity is studied, using the equations of hydrodynamics; only radial motions are considered, and the heat, chemical, and radiative-transfer equations are solved simultaneously with the hydrodynamic equations. The relevant chemistry is described along with the thermal model, the radiative-transfer process, and the numerical methods employed. Results for a contracting cloud are discussed in terms of the problem of initial conditions, the dynamical evolution of the cloud, its chemical and thermal evolution, time scales, and column densities. It is shown that the chemical evolution of a massive contracting diffuse cloud is sensitive to such physical properties as temperature and ion abundances, that warm and cool versions of a typical cloud evolve differently, and that the physical origin of this effect is the level of heating due to H2 formation on interstellar dust grains.

Gerola, H.↗

Intercalibration of Meteorological Satellite Imagers Using VIRS, ATSR-2 and MODIS

Global retrievals of surface, cloud and radiative properties from geostationary (GEO) and low-Earth-orbit (LEO) meteorological satellites require accurate calibration of their imagers. An accurate and consistent calibration increases the reliability and effectiveness of long-term monitoring of climate changes. More emphasis has been placed on calibrating the thermal infrared (IR) channel. The lack of on-board calibration in the visible (VIS) channel has prompted efforts to characterize the degradation of the VIS sensor using vicarious post-launch calibration techniques that measure bright stable desert targets from space and aircraft or using satellite-to-satellite normalizations. While such inter-calibrations are valuable and widely used, the lack of a well-characterized calibration reference source and the lengthy time delay between updates have minimized their effectiveness in climate monitoring. To address these shortcomings, this paper examines the use of research satellite imagers to provide stable calibration references for the visible (VIS, approximately 0.65 micrometers) channels and develops a method for rapid intercalibration of existing satellites. Calibration coefficients are determined for the Geostationary Operational Environmental Satellites (GOES-8 to GOES-10), Geostationary Meteorological Satellite (GMS-5), Meteosat-7, and the NOAA-14 Advanced Very High Resolution Radiometer (AVHRR). As a reference calibration source, this technique uses the self-calibrating sensors on the Tropical Rainfall Measuring Mission (TRMM) Visible Infrared Radiometers (VIRS) or the ERS-2 Along Track Scanning Radiometer (ATSR-2). GOES-8 is calibrated with VIRS and then its calibration is transferred to other GEO or LEO satellites. The absolute accuracy of this technique relies on the assumption that the on-board calibration is stable and well maintained. Minnis et al. assessed the VIRS calibration using comparisons with other self-calibrated satellite sensors including the broadband Clouds and Earth's Radiant Energy System (CERES) scanners, the ERS-2 Along Track Scanning Radiometer (ATSR-2), and the Terra Moderate-resolution Imaging Spectrometer (MODIS). Thus, the VIRS data can be confidently used as the initial reference source.

Nguyen, Louis↗

An Assessment of the Surface Longwave Direct Radiative Effect of Airborne Dust in Zhangye China During the Asian Monsoon Year Field Experiment (2008)

Tiny suspensions of solid particles or liquid droplets, called aerosols, hover in earth's atmosphere and can be found over just about anywhere including oceans, deserts, vegetated areas, and other global regions. Aerosols come in a variety of sizes, shapes, and compositions which depend on such factors as their origin and how long they have been in the atmosphere (i.e., their residence time). Some of the more common types of aerosols include mineral dust and sea salt which get lifted from the desert and ocean surfaces, respectively by mechanical forces such as strong winds. Depending on their size, aerosols will either fall out gravitationally, as in the case of larger particles, or will remain resident in the atmosphere where they can undergo further change through interactions with other aerosols and cloud particles. Not only do aerosols affect air quality where they pose a health risk, they can also perturb the distribution of radiation in the earth-atmosphere system which can inevitably lead to changes in our climate. One aerosol that has been in the forefront of many recent studies, particularly those examining its radiative effects, is mineral dust. The large spatial coverage of desert source regions and the fact that dust can radiatively interact with such a large part of the electromagnetic spectrum due to its range in particle size, makes it an important aerosol to study. Dust can directly scatter and absorb solar and infrared radiation which can subsequently alter the amount of radiation that would otherwise be present in the absence of dust at any level of the atmosphere like the surface. This is known as radiative forcing. At the surface dust can block incoming solar energy, however at infrared wavelengths, dust acts to partially compensate the solar losses. Evaluating the solar radiative effect of dust aerosols is relatively straightforward due in part to the relatively large signal-to-noise ratio in the measurements. At infrared wavelengths, on the other hand, the effect is rather difficult to ascertain since the measured dust signal level is on the same order as the instrumental uncertainties. Although the radiative impact of dust is much smaller in the infrared, it can still have a noticeable influence on the distribution of energy in the Earth-atmosphere system. This is mainly attributed to the strong light-absorptive properties commonly found in many earth minerals.

Hansell, Richard A.↗

Research concerning the net flux of radiation in the atmosphere of Jupiter

The plan of the NFR (Net Flux of Radiation) team is for the data from the two solar channels (B and E) of NFR to be reduced with the goal of determining the solar heating rate. In order to determine the solar heating rate from the NFR measurements, effects due to the instrument's spatial and spectral response functions, to the temperature variation of the instrument (and associated drift of calibration), to the setting sun, and to the rotation of the probe (initially at a rate comparable to the NFR sampling frequency), all must be well modelled. In the past year, a forward modeling routine was created to simulate NFR data return in the B and E channels. The effects of varying parameters describing the atmospheric model (such as cloud location and thickness) and the descent profile (such as rotation rate) were investigated and an inversion routine was developed. For the forward modeling, existing radiative transfer codes were used to determine intensity fields within the Jovian atmosphere. A routine was developed to determine instantaneous instrument response by integrating the intensity field over the instrument response functions. A second routine was developed to determine the actual output of the NFR by integrating along an arbitrary descent trajectory. Near the top of the atmosphere, the upflux data alone are used to constrain the cloud structure of he atmosphere. To accomplish this, models are used to describe the variation in up flux between consecutive measurements in terms of variations of cloud opacity and variations in known parameters such as the solar zenith angle. This allows us to develop a zero-order model of cloud structure. Lower in the atmosphere, at levels where there is little or no azimuthal structure to the net flux measurements, both the up flux and net flux are used to derive layer transmission and reflection functions, which then determine layer opacity and single scattering albedo. A preliminary analysis of the data began in December 1995. In these data we could see the rapid oscillations expected at the beginning of the data due to probe rotation and the sun passing through the edge of the field of view. In addition, the time when this oscillation stopped was clearly visible. This sets the rough optical depth above the probe at this time.

Tomasko, M. G.↗

Autonomous, Full-Time Cloud Profiling at Arm Sites with Micro Pulse Lidar

Since the early 1990's technology advances permit ground based lidar to operate full time and profile all significant aerosol and cloud structure of the atmosphere up to the limit of signal attenuation. These systems are known as Micro Pulse Lidars (MPL), as referenced by Spinhirne (1993), and were first in operation at DOE Atmospheric Radiation Measurement (ARM) sites. The objective of the ARM program is to improve the predictability of climate change, particularly as it relates to cloud-climate feedback. The fundamental application of the MPL systems is towards the detection of all significant hydrometeor layers, to the limit of signal attenuation. The heating and cooling of the atmosphere are effected by the distribution and characteristics of clouds and aerosol concentration. Aerosol and cloud retrievals in several important areas can only be adequately obtained with active remote sensing by lidar. For cloud cover, the height and related emissivity of thin clouds and the distribution of base height for all clouds are basic parameters for the surface radiation budget, and lidar is essetial for accurate measurements. The ARM MPL observing network represents the first long-term, global lidar study known within the community. MPL systems are now operational at four ARM sites. A six year data set has been obtained at the original Oklahoma site, and there are several years of observations at tropical and artic sites. Observational results include cloud base height distributions and aerosol profiles. These expanding data sets offer a significant new resource for cloud, aerosol and atmospheric radiation analysis. The nature of the data sets, data processing algorithms, derived parameters and application results are presented.

Spinhirne, James D.↗

Asian Dust Storm Outbreaks: A Satellite-Surface Perspective

Airborne dusts from northern China contribute a significant part of the air quality problem and, to some extent, regional climatic impact in Asia during springtime. Asian dust typically originates in desert areas far from polluted urban regions. During the transport, dust layers can interact with anthropogenic sulfate and soot aerosols from heavily polluted urban areas. Added to the complex effects of clouds and natural marine aerosols, dust particles reaching the marine environment can have drastically different properties than those from the source. Thus, understanding the unique temporal and spatial variations of Asian dust is of special importance in regional-to-global climate issues (e.g., radiative forcing, hydrological cycle, and primary biological productivity in the mid-Pacific Ocean, etc.), as well as societal concerns (e.g., adverse health effects to humans). The Asian dust and air pollution aerosols can be detected by its colored appearance on current Earth observing satellites (e.g., MODIS, SeaWiFS, TOMS, etc.) and its evolution monitored by satellites and surface network (e.g. AERONET, SKY NET, MPLNET, etc.). Recently, many field campaigns (e.g., ACE-Asia-2001, TRACEP-2001, ADE-2002 & -2003, APEX-2001 & -2003, etc.) were designed and executed to study the compelling variability in spatial and temporal scale of both pollution-derived and naturally occurring aerosols, which often exist in high concentrations over eastern Asia and along the rim of the western Pacific. I will present an overview of the outbreak of Asian dust storms from space and surface observations and to address the climatic effects and societal impacts.

Tsay, Si-Chee↗

The Footprints of 16 Year Trends of Arctic Springtime Cloud and Radiation Properties on September Sea Ice Retreat

The most prominent September Arctic sea ice decline over the period of 2000–2015 occurs over the Siberian Sea, Laptev Sea, and Kara Sea. The satellite observed and retrieved sea ice concentration (SIC) and cloud/radiation properties over the Arctic (70°–90°N) have been used to investigate the impact of springtime cloud and radiation properties on September SIC variation. Positive trends of cloud fractions, cloud water paths, and surface downward longwave flux at the surface over the September sea ice retreat areas are found over the period of 1 March to 14 May, while negative trends are found over the period of 15 May to 28 June. The spatial distributions of correlations between springtime cloud/radiation properties and September SIC have been calculated, indicating that increasing cloud fractions and downward longwave flux during springtime tend to enhance sea ice melting due to strong cloud warming effect. Surface downward and upward shortwave fluxes play an important role from May to June when the onset of sea ice melting occurs. The comparison between linearly detrended and nondetrended of each parameter indicates that significant impact of cloud and radiation properties on September sea ice retreat occurs over the Chukchi/Beaufort Sea at interannual time scale, especially over the period of 31 March to 29 April, while strongest climatological trends are found over the Laptev/Siberian Sea.

Arctic sea ice trend↗

Chemistry in interstellar space

The particular characteristics of chemistry in interstellar space are determined by the unique environmental conditions involved. Interstellar matter is present at extremely low densities. Large deviations from thermodynamic equilibrium are, therefore, to be expected. A relatively intense ultraviolet radiation is present in many regions. The temperatures are in the range from 5 to 200 K. Data concerning the inhibiting effect of small activation energies in interstellar clouds are presented in a table. A summary of measured activation energies or barrier heights for exothermic exchange reactions is also provided. Problems of molecule formation are discussed, taking into account gas phase reactions and surface catalyzed processes.

Donn, B.↗

Size and density distribution of very small dust grains in the Barnard 5 cloud

The effects of the temperature fluctuations in small graphite grains on the energy spectrum and the IR surface brightness of an isolated dust cloud heated externally by the interstellar radiation field were investigated using a series of models based on a radiation transport computer code. This code treats self-consistently the thermal coupling between the transient heating of very small dust grains and the equilibrium heating of conventional large grains. The model results were compared with the IRAS observations of the Barnard 5 (B5) cloud, showing that the 25-micron emission of the cloud must be produced by small grains with a 6-10 A radius, which also contribute about 50 percent to the observed 12-micron emission. The remaining 12 micron flux may be produced by the polycyclic aromatic hydrocarbons. The 60-and 100-micron radiation is dominated by emission from large grains heated under equilibrium conditions.

Lis, Dariusz C.↗