Even though vertical motion is resolved within convection-permitting models, recent studies have demonstrated significant departures in predicted storm updrafts and downdrafts when compared with Doppler observations of the same events. Several previous studies have attributed these departures to shortfalls in the representation of microphysical processes, in particular those pertaining to ice processes. Others have suggested that our inabilities to properly represent processes such as entrainment are responsible. Wrapped up in these issues are aspects such as the model grid resolution, as well as accuracy of models to correctly simulate the environmental conditions. Four primary terms comprise the vertical momentum equation: advection, pressure gradient forcing, thermodynamics and turbulence. Microphysical processes including their impacts on latent heating and their contributions to condensate loading strongly impact the thermodynamic term. The focus of this study is on the thermodynamic contributions to vertical motion, the shortfalls that arise when modeling this term, and the observations that might be made to improve the representation of those thermodynamical processes driving convective updrafts and downdrafts.
Recent technological advances have enabled the miniaturization of microwave instruments (radars and radiometers) so they can fit on very small satellites, with enough capability to measure atmospheric temperature, water vapor and clouds. The miniaturization makes these systems inexpensive enough to allow scientists to contemplate placing several examples in low-Earth orbit concurrently, to observe atmospheric dynamics in clouds and storms. To identify the most important weather and climate problems that can be addressed with these new observations, and to develop corresponding observation strategies using these "distributed" systems, specific analyses were conducted and used to justify "distributed" measurement requirements and quantify their expected performance. This presentation will describe the types of convoys, the expected observations, and their applications.
Numerical climate and weather models depend on measurements from space-borne satellites to complete model validation and improvements. Precipitation profiling capabilities are currently limited to a few instruments deployed in Low Earth Orbit (LEO), which cannot provide the temporal resolution necessary to observe the evo- lution of short time-scale weather phenomena and improve numerical weather prediction models. A constellation of cloud- and precipitation-profiling instruments in LEO would provide this essential capability, but the cost and timeframe of typical satellite platforms and instruments constitute a possibly prohibitive challenge. A new radar instrument architecture that is compatible with low-cost satellite platforms, such as CubeSats and SmallSats, has been designed at JPL. Its small size, moderate mass and low power requirement enable constellation missions, which will vastly expand our ability to observe weather systems and their dynamics and thermodynamics at sub-diurnal time scales down to the temporal resolutions required to observe developing convection. In turn, this expanded observational ability can revolutionize weather now-casting and medium-range forecasting, and enable crucial model improvements to improve climate predictions.
ACE is a proposed Tier 2 NASA Decadal Survey mission that will focus on clouds, aerosols, and precipitation as well as
ocean ecosystems. The primary objective of the clouds component of this mission is to advance our ability to predict
changes to the Earth’s hydrological cycle and energy balance in response to climate forcings by generating observational
constraints on future science questions, especially those associated with the effects of aerosol on clouds and
precipitation. ACE will continue and extend the measurement heritage that began with the A-Train and that will continue
through Earthcare. ACE planning efforts have identified several data streams that can contribute significantly to
characterizing the properties of clouds and precipitation and the physical processes that force these properties. These
include dual frequency Doppler radar, high spectral resolution lidar, polarimetric visible imagers, passive microwave and
submillimeter wave radiometry. While all these data streams are technologically feasible, their total cost is substantial
and likely prohibitive. It is, therefore, necessary to critically evaluate their contributions to the ACE science goals. We
have begun developing algorithms to explore this trade space. Specifically, we will describe our early exploratory
algorithms that take as input the set of potential ACE-like data streams and evaluate critically to what extent each data
stream influences the error in a specific cloud quantity retrieval.
In recent years, it has been revealed that the cloud microphysical properties such as cloud particle radii
obtained from satellite remote sensing were of apparent values. A combined use of passive and active sensor has
gradually revealed about what we observed using passive imager thorough the vertical information of clouds
obtained from active sensors. For understanding the process of cloud growth in nature, model that simulates cloud
droplet growth is also needed. Observation results obtained from the satellite remote sensing are used for
validating model such as cloud resolving model and spectral-bin microphysics cloud model. Vice-versa, models
are used for understanding the process that are hidden in satellite-remote sensing results. We are aiming consistent
understanding of clouds with observation and modeling.
In this paper, we will introduce a preliminary result of multi-sensor view of warm water clouds and we
will review our research strategy of cloud sciences, using satellite remote sensing, the cloud growth model, and the
radiative transfer.
The capabilities for observing clouds, precipitation and processes connected to condensed water in
the atmosphere by satellites that presently orbit the Earth is unprecedented in the history of spaceborne
Earth observations. The so-called A-Train of satellites (Stephens et al., 2002), in particular,
represents entirely new observations of key cloud and precipitation processes in a way more
advanced that ever before. These new observations represent a unique source of information for
evaluating the moist physics parameterizations in models with benefits that are expected to lead to
greatly improved and more realistic representations of these important atmospheric processes. This
paper outlines a collection of the new findings from the A-Train observing system.
This paper documents the development of the first integrated data set of global vertical profiles of clouds, aerosols, and
radiation using the combined NASA A-Train data from the Aqua Clouds and Earth's Radiant Energy System (CERES)
and Moderate Resolution Imaging Spectroradiometer (MODIS), Cloud-Aerosol Lidar and Infrared Pathfinder Satellite
Observations (CALIPSO), and CloudSat. As part of this effort, cloud data from the CALIPSO lidar and the CloudSat
radar are merged with the integrated column cloud properties from the CERES-MODIS analyses. The active and
passive datasets are compared to determine commonalities and differences in order to facilitate the development of a
3-dimensional cloud and aerosol dataset that will then be integrated into the CERES broadband radiance footprint.
Preliminary results from the comparisons for April 2007 reveal that the CERES-MODIS global cloud amounts are, on
average, 0.14 less and 0.15 greater than those from CALIPSO and CloudSat, respectively. These new data will provide
unprecedented ability to test and improve global cloud and aerosol models, to investigate aerosol direct and indirect
radiative forcing, and to validate the accuracy of global aerosol, cloud, and radiation data sets especially in polar regions
and for multi-layered cloud conditions.
The notion of the A-Train constellation of satellites is described. This constellation includes five satellites with EOS Aqua and EOS Aura at each end of the constellation and another small satellite, PARASOL, carrying the POLDER polarimeter inserted in the formation between the larger EOS spacecraft. This constellation also includes the CloudSat and CALIPSO spacecraft that were inserted into the Aqua orbit on April 28th, 2006. This newly formed constellation, together with the earlier NASA TRMM mission, represent a new age of remote sensing of clouds and precipitation in that we are now able to combine the observations of active radar and laser systems with passive radiometric observations. This paper reviews a few selected but commonly used remote sensing approaches for observing clouds and precipitation and highlights the potential of the new observing capabilities of the A-Train. It is also highlighted how this new era provides us with the opportunity to move away from present artificial practices of 'observing' and analyzing clouds and precipitation as separate entities toward a more unified approach to observe clouds and precipitation properties jointly.
The clouds of Earth are fundamental to most aspects of human life. Through production
of precipitation, they are essential for delivering and sustaining the supplies of fresh
water upon which human life depends. Clouds further exert a principal influence on the
planet's energy balance. It is in clouds that latent heat is released through the process of
condensation and the formation of precipitation affecting the development and evolution
of the planet's storm systems. Clouds further exert a profound influence on the solar and
infrared radiation that enters and leaves the atmosphere, further exerting profound effects
on climate and on forces that affect climate change (Stephens, 2005). It is for these
reasons, among others, that the need to observe the distribution and variability of the
properties of clouds and precipitation has emerged as a priority in Earth observations.
Most past and current observational programs are contructed in such a way that clouds
and precipitation are treated as separate entities. Nature does not work this way and there
is much to be gained scientifically in moving away from these artificial practices toward
observing clouds and precipitation properties jointly. We are now embarking on a new
age of remote sensing of clouds and precipitation using active sensors, starting with the
tropical rainfall measurement mission (TRMM) and continuing on with the A-Train
(described below). This new age provides us with the opportunity to move away from
past and present artificial observing practices offering a more unified approach to
observing clouds and precipitation properties jointly.
A scene dependent sensitivity analysis of top of the atmosphere near infrared radiances and polarized radiances to aerosol optical depth was performed. The analysis was performed for the hemisphere of viewing angles. The analysis includes a comprehensive examination of errors resulting from both the assumed aerosol size distribution and optical properties, as well as radiative transfer model assumptions. Three parameters are introduced. These parameters are the signal, the noise and the signal to noise ratio. The angular structure, as well as the angular averages of these parameters, are examined. It was found that, on the average, the top of the atmosphere signal to noise ratio is roughly three times larger for the radiances than for the polarized radiances. As a result, it was concluded that the majority of the information in the retrieval of optical depth is contained in the intensity measurements. The error analysis was used in the development of a two-channel optimal estimation retrieval of aerosol optical depth which utilizes the intensities only. Noise free and noisy synthetic radiances created from radiative transfer simulations are used to analyze the performance of the retrieval. Biases due to a priori constraints, viewing geometry, and forward model noise are analyzed.
Extensive sensitivity and error characteristics of a recently developed optimal estimation retrieval algorithm which simultaneously determines aerosol optical depth (AOD), aerosol single scatter albedo (SSA) and total ozone column (TOC) from ultra-violet irradiances are described. The algorithm inverts measured diffuse and direct irradiances at 7 channels in the UV spectral range obtained from the United States Department of Agriculture's (USDA) UV-B Monitoring and Research Program's (UVMRP) network of 33 ground-based UV-MFRSR instruments to produce aerosol optical properties and TOC at all seven wavelengths. Sensitivity studies of the Tropospheric Ultra-violet/Visible (TUV) radiative transfer model performed for various operating modes (Delta-Eddington versus n-stream Discrete Ordinate) over domains of AOD, SSA, TOC, asymmetry parameter and surface albedo show that the solutions are well constrained. Realistic input error budgets and diagnostic and error outputs from the retrieval are analyzed to demonstrate the atmospheric conditions under which the retrieval provides useful and significant results. After optimizing the algorithm for the USDA site in Panther Junction, Texas the retrieval algorithm was run on a cloud screened set of irradiance measurements for the month of May 2003. Comparisons to independently derived AOD's are favorable with root mean square (RMS) differences of about 3% to 7% at 300nm and less than 1% at 368nm, on May 12 and 22, 2003. This retrieval method will be used to build an aerosol climatology and provide ground-truthing of satellite measurements by running it operationally on the USDA UV network database.
Clouds play an important role in the hydrologic cycle, influence global energy balance, and represent a significant yet poorly understood component of global climate change. As a result, quantitative global observations of liquid and ice cloud microphysical and radiative properties continue to be a focus of a growing number of satellite-based sensors each having an associated suite of retrieval algorithms. While a number of these algorithms have successfully been applied to map clouds, many can only be applied under specific conditions (eg. during the daytime) or over a limited dynamic range (eg. optically thin cirrus) often leading to unphysical discontinuities when one seeks to compile a complete picture of the global distribution of clouds. Furthermore, discrepancies exist between products of different algorithms when they are applied to the same scene by virtue of differences in the information provided by distinct combinations of measurements.
This paper revisits the problem of cloud microphysical property
retrievals from satellite radiance observations at solar and thermal
wavelengths in an effort to quantify their information content with
respect to single layer liquid and ice clouds over an oceanic
background. Using the channels on the Moderate Resolution Imaging
Spectroradiometer (MODIS) as an example, it will be demonstrated that
an entropy-based definition of information content provides a useful
metric for evaluating the utility of a set of observations in a
retrieval problem. This approach is used to objectively determine the
subset of wavelengths that provide the greatest amount of information
for oceanic microphysical property retrievals from the MODIS
instrument. The results show that the combination of a conservative and a non-conservative scattering shortwave channel in concert with a near-infrared channel, an infrared window channel, and one in the wings of the 15 m CO2 band provide the optimal channel combination for the wide variety of liquid and ice clouds examined. With an eye toward developing a coherent representation of the global distribution of cloud microphysical and radiative properties, this combination of channels may be integrated into a suitable multi-channel inversion methodology such as the optimal estimation or Bayesian techniques to provide a means of establishing a common framework for cloud retrievals under varying conditions. Under some circumstances, other channels may provide a small amount of additional information but in most cases the remaining channels only supply redundant information and do not justify the additional computation cost required to integrate them into an algorithm.
A method of retrieving cloud microphysical properties using combined observations from both cloud lidar and radar is introduced. This retrieval makes use of a variation on the traditional optimal estimation retrieval method, whereby a series of corrections are applied to the state vector during the search for an iterative solution. The retrieval method is applied to lidar and radar observations from the CRYSTAL-FACE experiment, and vertical profiles of ice crystal characteristic diameter, number concentration, and ice water content are retrieved for a cirrus cloud layer observed during the experiment.
Pertinent issues concerning cloud-radiation interactions that are relevant to studies of climate are discussed in terms of cloud optical properties. These optical properties are classified either inherent or apparent; the former are functions of cloud microphysics, the latter come about from the illumination of the cloud by radiation. The connection between the two sets of optical properties is discussed under the format of radiative transfer. The state of our lack of understanding of this connection is illustrated using examples derived from recent observational studies. Further evidence is presented that questions the validity of one dimensional radiative transfer theory as applied to the earth's atmosphere.
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