2. SCIENCE GOALS AND QUESTIONS
3. NASA EARTH SCIENCE PRIORITIES AND RESEARCH OBJECTIVES
4. CLIMATE OBSERVING BENEFITS IN THE EOS ERA
5. WEATHER OBSERVING BENEFITS IN THE NEXT DECADE
6. GEO SYNERGY WITH LEO
7. CHARTER OF THE ADVANCED GEOSYNCHRONOUS STUDIES GROUP
This manuscript describes the benefits that would result from advanced geosynchronous satellite observations, both for Earth science research and for the operational analysis of weather and climate.
The Earth has many fast and slow modes, and slow modes. The fast modes are called "weather" (e.g. temperature, humidity, clouds, precipitation, radiation), especially on the local scale. The slow modes (e.g. soil, vegetation, rivers, lakes, oceans, ice, and greenhouse gasses) are called "climate", especially on the global scale. All these weather and climate modes, scales, and processes interact significantly.
If we hope to make reliable predictions of weather and climate, we have to monitor land, sea, and air on their natural scales. The main energy pumps are the annual and diurnal cycles, each with comparable driving power. The Earth's response to the cyclical solar drivers is episodic and irregular. Therefore, we must resolve not only the seasonal cycle for many years, but also variations in the diurnal response cycle, and the irregular exchanges (storms) over the globe.
Unfortunately for analysts, changes by only a few percent in some rapidly varying components are significant for weather and climate (e.g. atmospheric temperature, cloudiness, ozone). Consequently, continual large-scale coverage with careful calibration and cross-correlation among all instruments is vital for determining variability and trends.
Scale interactions often involve chaotic processes that are not easily simulated by global numerical models. Therefore, a vigorous world-wide campaign of large-scale, uniform observations of land-sea-air behavior has been undertaken by the USGCRP, with the goal of creating a long-term database while the Earth system varies during the next few decades. The slower, large-scale processes will be observed by in-situ instruments and polar-orbiting remote sensing satellites. However, the more rapid hourly variations in critical components (clouds, winds, aerosols, water vapor, precipitation, temperature, etc.) are more difficult to sample uniformly over the globe, and have no associated research satellites.
Fortunately, NOAA's current GOES operational weather satellites , and to a lesser extent similar satellites from other countries, already measure to a certain degree many of the fast "climate" variables clouds, winds, temperature, water vapor, precipitation proxies, and surface conditions every 3 hours over the western hemisphere. In order to improve our understanding of climate processes and associated atmospheric and surface phenomena additional geosynchronous observations are required.
As forecasters and researchers focus more on monitoring and forecasting rapidly evolving weather processes, the need for improved geosynchronous observations with improved spectral, temporal and spatial resolution becomes more critical. To continue NOAA's current pace of progress in using the science-service link to improve their forecast services, well-calibrated digital data sets from geosynchronous satellites must be available for assimilation into numerical models and for use in the issuance of warnings and short term forecasts at NWS field offices.
Therefore, to meet the needs of both the research and operational communities the Advanced Geosynchronous Studies (AGS) program was initiated in 1997 to develop technologies and system concepts for Earth observation from geosynchronous orbit for the benefit of both the research and operational communities. It is jointly sponsored by the NASA Earth Science Systems Program Office and NOAAs Geostationary Operational Environmental Satellite (GOES) program.
This manuscript: 1) describes the use of geosynchronous observations for research studies, 2) lists overall science goals and science questions that can be addressed from geosynchronous orbit, 3) reviews NASAs science priorities and research objectives, 4) discusses the "value added" to low-orbit observations by corresponding geosynchronous observations, 5) outlines the weather observing needs of the National Weather Service, 6) compares the satellite-observable parameters from EOS and a possible advanced geosynchronous satellite, and 7) describes the charter of the newly formed NASA-NOAA group for Advanced Geosynchronous Studies (AGS).
The overall science goal of AGS is the increased understanding of physical, chemical and dynamical processes in the Earths atmosphere and at the planets surface.
The more specific goals are to:
Many weather and climate questions involve the most highly variable components of the Earth system clouds, water vapor, aerosols, precipitation, fires, volcanoes, chemical constituents, surface temperature, etc.. Observational systems, such as geosynchronous satellites, that fully observe these processes with the fine time resolution required can address many fundamental science questions that are difficult or impossible to answer from observations at a time resolution of once or twice per day.
The following are high priority science questions that require observations from geosynchronous orbit:
* How do the large-scale atmospheric circulations interact with the hurricane vortex?
* Why do upper-level troughs lead to storm intensification in some cases and weakening in other cases?
* What is the role of baroclinic processes in hurricane track and intensity changes?
* What role does the deep tropospheric moisture distribution in the hurricane environment play in determining relative intensity and distribution of precipitation (i.e., what are the environmental differences between heavy and modest rain-producing hurricanes)?
* What are the roles of convective outbursts in the inner core region (inside and including the eye wall) and outer region (outside the eye wall) in hurricane intensity change?
* What are the roles of upper tropospheric dry slots in the intensification of extratropical cyclones and how do they relate to upper tropospheric fronts and tropopause folds?
* How do frontal systems interact with topography? To what extent are the deep tropospheric frontal structures maintained or modified as they cross the Rocky Mountains?
* How are rainbands related to upper and lower tropospheric fronts, particularly in the lee of steep mountain ranges?
* How is the rainfall distribution and intensity related to rapid intensification of extratropical cyclones?
* What are the processes associated with secondary cyclogenesis along fronts?
These questions and more are discussed in the following two sections on the benefits of advanced geosynchronous observations to climate and weather.
As NASA's part in the U.S. Global Change Research Program (USGCRP), the Earth Science (ES) program has identified five scientific priorities and corresponding research objectives that it will pursue in 1996-2002.
The following quotations from ES's 1996 science research plan underline the priorities and objectives that are reasonably observable from geosynchronous orbit (i.e. not sea ice or ocean topography):
Each of the five ES research areas has scientific questions about variability and trends in land-water-air constituents. There are several technical solutions for obtaining each answer. Consequently, NASA's Earth Observing System (EOS) satellites carry many instruments designed to collect information about the variable constituents and interactive processes that shape the planet. Some of these constituents and processes change so rapidly that ESs research objectives require hourly time resolution, as discussed in the following section.
EOS will collect a 15 year record of measurements of parameters of the earth system aerosol concentration, cloud fraction, cloud microphysics, water vapor distribution, temperature distribution, fire occurrence, vegetation cover and primary productivity over the land, ocean productivity, etc. It will collect the information two times a day for the AM platform (e.g. 10:30 am and 10:30 pm) and four times a day for measurements that will be repeated in the PM Platform at 1:30 pm and 1:30 am). For some earth parameters that have a rate of change of a day or slower, e.g. vegetation, this measurement strategy is satisfactory. But for other measurements, e.g. clouds, water vapor, fires, convective systems and cyclonic storms with rate of change of minutes to hours, there is a strong short-term variability that needs to be measured in order to understand the role of these parameters in climate change. We anticipate the strong variability to be somewhat more important over the land and coastal regions than over the ocean where the diurnal cycle of the solar heating is largely compensated by the large ocean heat capacity. Geostationary satellites are required to measure these highly variable Earth system parameters and also establish their diurnal cycle and the seasonal and interannual variability of their daily cycle. A synergism between geosynchronous and polar satellites will provide the full spatial and temporal coverage required to measure changes in the earth system and its climate, where the geosynchronous satellites will concentrate on the most transient earth system parameters, discussed in the following subsections.
Clouds are one of the most uncertain feedback mechanisms in the climate change process. While only recently discovered to have a net cooling effect, their impact on climate is quite variable since the balance between the cooling effect by reflecting sunlight to space and the warming greenhouse effect depends on the cloud height and thickness. Climate change (global or regional) may result in changes in the cloud system that may serve as a strong feedback mechanism, positive for an increase in the high cloud fraction or negative for low cloud fraction. This may enhance or decrease, respectively, climate change from greenhouse gases. For example, an increase in the fraction of low-level stratiform clouds by 1%, during the last century may already explain the difference between the measured warming of ~0.5K and the predicted warming of ~1K. If the EOS 15 year record detects a correlation between the warming trend and an increase in the low cloud fraction, a question may still remain whether the increase is a real increase in the total cloud fraction, and therefore an increase in the reflection of sunlight back to space, or just a shift in the diurnal cycle of the cloud fraction that at 10:30 am results in an apparent increase in the cloud fraction for the entire day. Large-scale measurements of the diurnal cycle of these clouds and of a change in the diurnal cycle may resolve this issue. Although this can, in part, be accomplished with precessing orbits such as that used with TRMM, the geosynchronous viewpoint will give much higher spatial and temporal resolvability of the diurnal signal due to the much higher time resolution. For example, from geosynchronous orbit the diurnal signal for even a single day can be resolved, while the TRMM-like orbit requires sampling over a long period and/or over a large domain.
Cloud microphysics affects the interaction of clouds with sunlight and controls the rate of precipitation and, therefore, the cloud lifetime. Cloud microphysics are affected by the concentration and properties of aerosol particles that originate from human and natural sources and also by atmospheric dynamics. EOS will measure the cloud phase and the cloud drop size. Resolving the diurnal cycle of these cloud properties is required to for understanding the impact of aerosol on climate through cloud modification (considered today one of the main uncertainties in climate forcing -IPCC, 1996). Again, we need to know if the interannual change in the cloud properties is due to a real change and not a shift in the diurnal cycle. Since most anthropogenic aerosol is produced over land, the interaction of aerosol with clouds over land is important and is expected to have a strong diurnal cycle.
4.2 Water Vapor
Without changes in the concentration and vertical distribution of water vapor the greenhouse effect on the temperature record would be ~4 times smaller. Therefore the precise response of concentration and distribution of water vapor in the atmosphere to climate change is a decisive feedback mechanism that may determine the importance, or lack thereof, of greenhouse warming. There is evidence that the parameterization of water vapor in climate models is too simple, so detailed measurements are very important. EOS plans to have measurements of total precipitable water vapor and separation into two levels in the AM platform and the best possible vertical structure that can be derived from passive remote sensing in the PM platform. But the diurnal cycle is still missing. The diurnal cycle of water vapor is very important over land, but may not be very important over the oceans.
4.3 Cloud Formation
EOS is planning simultaneous measurements of water vapor distribution, atmospheric temperature profile and aerosol, precursors to cloud formation and the resulting properties of clouds: droplet size and phase, height, cloud top temperature, and reflectance of sunlight. The measurements on the PM platform are more extensive than on the AM platform. It will measure all of the above cloud properties. Measurements of the variability of these properties during the day will be very important, especially for rapidly changing moisture and aerosols. For example, the 6 to 8 micron spectrum can be used to monitor the vertical distribution and motion of water vapor throughout the day.
Aerosol particles scatter and absorb solar radiation. They also serve as the condensation nuclei and ice particles of clouds. Therefore modification of the aerosol properties will cause modification of the cloud properties. Both the direct interaction of aerosol with solar radiation and the indirect interaction by modification of cloud properties generates a radiative forcing of climate, that, according to the IPCC reports (1992, 1994, 1996) represents the largest uncertainty in the radiative forcing of climate. Even though the aerosol forcing is probably half of that of the greenhouse gases, the absolute uncertainty in this forcing is about 4 times larger than the uncertainty in the greenhouse gases. The aerosol life time is very short (a few days) and their generation very dynamic, varying from hour to hour. Biomass burning aerosol is generated from fires, 80% of them in the tropics, with a very specific diurnal cycle (e.g. 12 pm to 5 pm) that varies from one region and ecosystem to another. Sulfate aerosol are produced from oxidation of sulfur dioxide emitted by industry and cars, oxidation that requires sun light, and therefore have a diurnal cycle. Dust is generated in desert and desert transition zones. It is affected by human induced overgrazing and is a function of the wind distribution, temperature profiles, and sunlight, and therefore should have a strong diurnal cycle. EOS will measure global aerosol mainly during the daylight hours, at 10:30 am for the AM platform and 1:30 pm for the PM platform. Measurements from the TOMS instrument taken once per day will enhance the aerosol measurements over the land and may help to separate between aerosol scattering and absorption over land and ocean. Supplementing this information with the full diurnal cycle from geostationary orbit is of great importance.
Fires are an indication of deforestation and of land use practices that affect both the land productivity and the atmospheric composition. Most fires are man-made and occur in the tropics, are rather small, and have a duration of up to a few hours. Fires of woody material (e.g. in deforestation) are of a longer duration and fires of grasslands and agricultural waste are of a shorter duration. Wild fires in the mid latitudes and northern regions (e.g. USA and Canada) are of major ecological importance. They are an essential part of these ecosystems, but are also a threat to populated regions directly as fire hazard or indirectly through the emission of polluting smoke. USA Forest Service has a complex policy regarding which fires to fight and which to let burn. This policy was very variable in the last century, resulting in even larger fires (e.g. Yellowstone fire). Presently the Forest Service fire treatment is based only on ground based and aircraft observations. The EOS MODIS instrument will have special fire channels that with a 1 km resolution will detect fires, establish the rate of combustion of biomass in these fires and may be able to distinguish between new flaming fires and old smoldering fires. But the information will only be provided up to 4 times a day (after the launch of PM). Supplementing this information with the geosynchronous diurnal cycle, even if with a lower spatial resolution, is very important and was proven critical in field experiments that concentrated on the biomass burning issue such as SCAR (Smoke, Clouds and Radiation conducted in the US and Brazil). In this respect, geosynchronous observations can supplement the EOS information by detecting and monitoring the diurnal cycle of the more energetic fires between the EOS observation times. This will be very useful for establishing the role of biomass burning in climate change and land use change and for helping to develop a new, more sophisticated policy for the Forest Service in its decision making and fire fighting. Geosynchronous observations can routinely provide information every 15 minutes on the location and strength of larger wild fires in the western hemisphere.
4.6 Trace Gases
There are several trace gases important for the greenhouse effect, for atmospheric chemistry, and for human health and safety: O3, CO, CH4, N2O, CO2, and SO2. EOS instruments will measure these during the overpasses of the AM and PM platforms. However, local weather is a significant factor controlling sources, sinks, diffusion, transport, and deposition patterns of trace gasses in the troposphere. Several of these gases have regional, diurnal, and sporadic behavior that require more frequent and continuous observation due to biological, photochemical, and even volcanic factors. For example, from geosynchronous orbit, one could observe the diurnal cycle of atmospheric ozone, including its spatial variability, horizontal transport, and vertical exchange associated with weather and climate processes.
4.7 Atmospheric Temperature and Humidity
The thermodynamic variables in the atmosphere change markedly during the day. Water vapor is particularly variable in the lower troposphere on time scales of hours. Water vapor is important not only to weather, but to radiative, photochemical, aerosol and land processes. The intervals between EOS atmospheric soundings could be supplemented with hourly high resolution soundings of temperature, moisture, cloud and moisture motion ("wind") observations for input into data assimilation and numerical prediction models on global and regional scales in order to evaluate dirurnal to interannual impacts.
4.8 Natural Hazards
Sporadic natural hazards like wildfires, lightning storms, and volcanic eruptions are far more easily captured from geosynchronous orbit than from polar-orbiting satellites. Volcanoes in the western Americas and Caribbean basin are readily observed from geosynchronous orbit. Volcanic smoke and ash can be readily detected and traced. With advanced instrumentation, volcanic gases can be identified and measured as they emerge and dissipate. Rapidly varying and deadly flash floods, severe thunderstorms, hurricanes and snowstorms are also best observed and monitored from geosynchronous orbit.
In-flight experience with lightning mapper data demonstrates that it is a useful proxy for intense convection related to ice flux, updraft strength, convective rainfall, diabatic and latent heating, and upper tropospheric water vapor. A lightning mapper is flying on the TRMM satellite. A geosynchronous LM is capable of filling in the enormous fraction of lightning not observed by TRMM over the great thunderstorm belts of the western hemisphere the southeastern United States, the Gulf of Mexico, the Inter-Tropical Convergence Zone (ITCZ), and the Amazon basin. Continuous observations from geosynchronous viewpoint provides a database to investigate seasonal, annual and interannual variability for studying short term climate change. With uniform day-and-night detection efficiency greater than 90% over large areas, a very complete lightning climatology of the western hemisphere will certainly be generated. Finally, for atmospheric chemistry, lightning plays a significant role in generating nitrous oxides. The natural nitrous oxide budget is a matter of great uncertainty at this time, and long-term observations of one of its sources will prove valuable as the subject develops.
Accurate estimation of precipitation is critical to many of the goals of global change and climate research and also to the goals of understanding atmospheric processes and weather-related natural hazards. Precipitation estimates are available based on passive microwave observations from polar-orbiting satellites such as the SSM/I instrument on the DMSP satellites and the soon-to-be-launched AMSU instrument on NOAAs polar orbiter. The Advanced Microwave Scanning Radiometer (AMSR), which will fly on EOS-PM and on ADEOS II, will improve precipitation estimates from polar orbit through increased resolution and additional, low-frequency channels. The Tropical Rainfall Measuring Mission (TRMM) provides the best rainfall estimations through high-resolution passive microwave observations combined with the first precipitation radar in space. Its low-inclined, precessing orbit allows the measurement of the diurnal cycle on a climatic scale.
However, precipitation is a quantity that varies extremely rapidly in both time and space. Therefore, there has been tremendous effort to estimate precipitation from proxy parameters available from geosynchronous observations. These parameters have typically been cloud characteristics obtained from visible and infrared observations, often combined with conventional information, for example sparse surface raingage data. Improvement of geosynchronous observation of precipitation, perhaps by use of remote observations physically more closely related to precipitation, or by better proxy parameters, would in turn improve precipitation analysis for a number of research areas. These key areas include the analysis of regional climate precipitation patterns, definition of the diurnal cycle of precipitation and the variation of the phase and amplitude of that cycle, and the interaction of precipitation and its associated latent heating with the dynamics of atmospheric systems.
In a time of diminishing resources and performance-based decisions, the NWS has set five science priorities that are directly linked to forecast issues in which relatively little progress has been made over the last 40 years, even with the incorporation of the model-based end-to-end forecast process (Uccellini, 1996). The top five NWS science priorities to support advanced short-term forecasting and warnings through the year 2005 include the study of the processes involved with:
The potential role that geostationary satellite data could play in leading to significant progress in these research areas is discussed below. Also included are a series of critical questions, related to each priority item, that must be answered before a clear definition of future operational geostationary requirements can be finalized.
5.1 Quantitative Precipitation Forecasting
Quantitative precipitation estimation derived from rain gages and multiple remote sensors is a critical first step to quantitative precipitation forecasting. A critical question emerges:
Radar and satellite both offer unique strengths for precipitation estimation but also have limitations. Radar data provides direct detection of precipitation but suffers from range limitations and non-uniform coverage. Satellite data (with the exception of microwave data), can only indirectly detect precipitation, but offers more uniform global coverage than radar. Likewise the unique strengths of polar and geostationary satellite data can be used to complement each other and compensate for the others weaknesses.
Satellite data is also an important factor in improving the prediction of precipitation from numerical models, leading to the question:
Passive IR sounders provide superior horizontal and vertical resolution but are limited to clear areas. Microwave sounders can provide information on temperature, liquid water and water vapor in cloudy areas but cannot match the resolution of the passive IR sounders.
Convective precipitation varies rapidly in time and space.
Satellite sounders are effective tools for determining total precipitable water in a vertical column, which is critical information for QPF. However, determining the vertical distribution of water vapor, especially in the low levels of the atmosphere, would provide additional value in the QPF process, leading to the question:
Commercial ground-based lightning detection processing systems are designed to display only cloud-to ground strokes and not the much more plentiful cloud-to-cloud flashes. Research has shown that an increase in lighting frequency typically precedes an increase in rainfall rate, which leads to the question:
5.2 The Effect of Topography on Local Weather Regimes
Results from the NWS Lake Effect Snow (LES) Study indicate that 4 km IR resolution is insufficient to detect individual wind-parallel LES bands.
Preliminary results from studies of LES events indicate that in some cases changes in cloud top glaciation correspond to changes in snowfall rate. Therefore, a more accurate measure of cloud-top glaciation should lead to improved estimates of snowfall rates from LES bands.
During the NWS LES study, passive IR sounders from GOES-8/9 were of only limited value. There were two basic problems: 1) coarse vertical resolution for defining the vertical distribution of water vapor and the low level stability, and 2) the absence of soundings in cloudy regions.
The use of the low-cloud product, produced by differencing GOES IR channel 2 (3.9 microns) from channel 4 (10.7 microns) has resulted in a quantum leap forward in forecasters ability to detect low clouds and fog at night. However with the 4 km resolution of the GOES IR imager data, narrow bands of valley fog still escape detection.
5.3 The Evolution and Movement of Tropical Cyclones
The use of high-density satellite-derived winds has demonstrated potential for improving forecasts of hurricane tracks. In experiments with the Hurricane Research Divisions barotropic forecast model (VICBAR), the satellite wind sets yielded modest improvements over control runs in nearly two-thirds of the 72-hour forecasts.
For a select number of cases, the use of satellite derived cloud track winds and water vapor winds has had a positive impact on the analyses of the wind fields surrounding hurricanes and subsequent improvement in numerical prediction.
Satellite moisture and temperature soundings are critical for defining the near storm environment. Presently, the operational areal coverage of the GOES sounders are limited such that if requirements for the ASOS cloud product are met, the areal coverage over the ocean is restricted. A faster sounder would lead to improved forecasts.
A microwave sounder in geostationary orbit would lead to improved tropical cyclone forecasts by providing soundings in cloud covered areas within the storm. Significant additional meteorological information regarding the strength of a hurricane lies in the magnitude of its warm core temperature anomaly and in the extent of its rain bands, both of which can be detected in microwave data (Staelin, 1997).
In-flight experience with lightning mapper data demonstrates that it is a useful proxy for intense convection related to ice flux, updraft strength, convective rainfall, diabatic and latent heating. This leads to the question:
5.4 Rapid Development of Wild Fires
The GOES channel 2 IR (3.9 micron) data is very sensitive to sub-pixel size hot spots (Menzel et al., 1994). As a result, large fires (at least 200 acres) and temperatures of 500K can be detected using enhanced 3.9 micron imagery (Purdom, 1996). While AVHRR is better suited for fire detection it is limited by its polar orbiting time scale.
Satellite imagers and sounders could provide valuable input to numerical models for the atmospheric conditions in the immediate vicinity of large fires.
5.5 Explosive Cyclogenesis
Over the past decade, there have been improvements in synoptic scale forecasting of rapidly deepening cyclones out to day 4. But improvements are needed in defining the mesoscale details of these storms both in the initial analysis and in the subsequent numerical forecasts. Velden (1992), Spencer et al. (1995), and Hirschberg et al. (1997) showed that microwave radiance analyses constructed from polar orbiter data are valuable diagnostic tools that can be used to monitor the progression of important cyclogenesis-related features and processes in the upper troposphere and lower stratosphere, especially when used in conjunction with other satellite-derived products such as ozone measurements. Significantly these microwave analyses are valid in regions of clouds and precipitation.
Gurka et al. (1995) demonstrated that the GOES imager water vapor data (6.7 microns), when used in conjunction with other data sources such as surface data, upper air data, and numerical model output, can aid in the detection and forecasting of explosive cyclogenesis.
5.6 NWS Needs for the Next Generation GOES Instruments
The last experimental geostationary satellite was ATS-3 in the early 1970s, and the last experimental sensor on a GOES satellite was the VISSR Atmospheric Sounder (VAS) first launched on GOES-4 in 1978. The lack of an experimental satellite as a prototype to the GOES-I through -M series resulted in unnecessary delays cost overruns, and lost opportunities. The answers to the critical questions presented in this section would be provided years earlier with the opportunities provided by a research oriented geostationary satellite. Furthermore, in order to answer the questions posed in the previous sections, it is necessary to utilize a geostationary satellite that is unencumbered by operational constraints. The present GOES-8, for example, has operational commitments to provide 4 imager views over the continental U.S. per hour and 1 full disk view every 3 hours. These schedule requirements are relaxed only for the operational monitoring of severe weather events at more frequent intervals. Research opportunities from the GOES satellites are severely limited. Furthermore, any instruments flown on the GOES satellites must have proven operational value. Once again there is very little room for experimentation.
To match expected advances in numerical weather forecasting, the NWS foresees at least a doubling of the space-, time- and spectral-resolution requirements for imaging and sounding from the GOES satellites during the next decade. Indeed, the space-time resolution of current weather models are already beginning to exceed the capabilities of the new GOES-8/9 satellites, designed in the early 1980's. Preliminary studies with the numerical forecast models at the European Center for Medium Range Forecasting (ECMWF) and at the National Center for Environmental Prediction (NCEP) show significant impact by hourly updates of mesoscale water vapor and wind data from geosynchronous satellites. There is also reason for optimism in expecting the current GOES sounding system to contribute to model forecast improvements. Nevertheless there is also reason to believe that current GOES limitations will inhibit the potential positive impacts over a large number of cases. To address this issue over the next decade, it is anticipated that NOAAs requirements for vertical temperature sounding accuracy will approach ±1 C in 1 km layers. An advanced sounder must carry both microwave temperature-moisture channels and a very high-resolution infrared radiometer in order to deliver useful data in both cloudy and cloud-free regions. In particular, microwave soundings of the cloudy north Pacific should have a noticeable impact on weather forecasts for the continental USA.
The demands on the future GOES imagers will be just as great. Frequently refreshed, high-quality, full-disk imaging is the NWS highest priority to support the forecast and warning program, especially as they relate to local forecast offices and national service centers.
Meteorological data products from an advanced imager would include:
An advanced imager could deliver performance that is twice as good as the current GOES imager, with radiometry similar to the polar orbiting imagers:
NOAA has identified a need to evaluate the value of real time lightning mapping in the next decade. Fortunately, the Lightning Mapper (LM) developed at NASA-MSFC is an engineering and scientific success now flying in space. A geo-ready version of LM could be developed, and a flight model readied within 2 years of full-funding, to fly in the GOES-N/O era (2001-2005 AD). Most cloud-to-cloud lightning can be observed from space 24 hours per day, providing an indicator of the convective onset of precipitation. This is a valuable indicator of vigorous storm development and energy release in regions outside the NEXRAD radars, such as in the Gulf of Mexico. LM data is easily integrated into real time meteorological analyses with NEXRAD and GOES imagery, and supports emergency warning systems.
Given all of these technical demands to meet the NWS operational forecast requirements being placed on geostationary satellites, an efficient, automated ground system must deliver geosynchronous observations to numerical models and to field forecasters in real-time, in a digital form ready for data fusion with other sources of real-time weather data. A well designed command-and-control advanced geostationary satellite system should be relatively autonomous and as easy to operate.
Finally, NASA and NOAA must justify the cost of expensive space-based systems. The connection between greater resolution and greater knowledge must be estimated by objective simulations. Scientific studies of the impact of a new imager, sounders, lightning mapper and ground system are just as important as the engineering studies that enable these instruments.
5.7 GEO Customers
NOAA operates GOES to make several data products and services. Many of these are delivered to other agencies, and the raw satellite data are publicly available both in real-time broadcasts and in digital archives. The current customers for geosynchronous data who would benefit from improved instrumentation are:
NOAA is the official archive agency of climate records in the United States. NOAA's climate analysis and forecast office will be its own best customer of a long, uniform series of high quality geosynchronous observations.
Parameters Observed from LEO and GEO
The 1996 ES science research plan targeted twenty-four environmental variables for systematic observation from low earth orbit (LEO). The following table lists those variables that are reasonably observable from LEO and from advanced geosynchronous earth orbit (GEO) remote sensors. The table gives more marks to the better determined variables expected from the EOS-funded LEO instruments and from potential advanced GEO instruments. The justification for these marks is debatable, of course, and must be addressed by systematic advanced geosynchronous studies.
|ENVIRONMENTAL VARIABLES (=best)||EOS LEO||Adv. GEO|
|radiative energy fluxes|||||
|land cover & land use|||||
|phytoplankton & dissolved organic matter|||||
|surface wind fields||||
|ocean surface topography||||
|ice sheet topography & ice volume change||||
|total solar irradiance|||||
|ultraviolet spectral irradiance|||||
Rows in the above table where GEO is within one mark of LEO are strong candidates for geosynchronous instrumentation, especially where the parameter has chaotic behavior and a strong diurnal cycle. In particular, GEO observations are an excellent source of information about rapidly changing clouds, winds and water vapor. The table also gives marks where new GEO instrumentation is feasible, but not on the AGS priority list for advanced observations.
6.2 Synergy between LEO and GEO Regional Studies
There are two high priority regions identified for ES case studies:
These regions are the standard operational targets for GOES. The vast and rapidly changing aerosols, clouds and rainfall in the Amazon are particularly well observed at nadir from GOES-EAST at 75W, while meagerly sampled by the EOS polar orbiters.
6.3 Synergy between LEO and GEO Instruments
The specific synergy between each of the proposed advanced geo-instruments with corresponding EOS and NPOESS instruments are:
6.4 Unique Information from GEO
Some specific information benefits from an advanced geosynchronous system are:
In the early 1990's, NASA commissioned a Geostationary Earth Observatory Study (GEOS) team to study the scientific utility of observations from geostationary orbit for understanding climate. The previous GEOS earth system science study concluded that:
"In many respects, the polar-orbiting instruments study the effects of processes, whereas the geostationary instruments can study the process itself."
6.5 Utilization of GEO and LEO Data by NWS
In the past, data from low earth-orbiters (LEO) have been used primarily for longer range prediction and climate issues, whereas data from geostationary satellites have been used in NWS forecast offices for issuing short term forecasts and warnings. Furthermore, while LEO data has been used primarily in a quantitative mode for input into numerical models, geostationary satellite data has been used primarily in a qualitative image mode by forecasters dealing with hazardous weather events such as tornadic storms and hurricanes.
This situation has begun to change due to a number of factors, including: 1) the launch of GOES-8 in April, 1994, carrying an advanced, operational 19 channel sounder; 2) continued improvements of LEOs planned for launch in the near future; and 3) general advancements in weather and climate forecasting. Requirements are now evolving that dictate the use of GOES data in a quantitative mode at national modeling centers for use in numerical prediction systems and at local forecast offices for producing derived product images (e.g. stability indices, total precipitable water, and the low cloud product). Furthermore, the utilization of LEO data is being extended beyond the national centers for use in local and regional forecast offices for the computation of specialized products (e.g. soil moisture and precipitable water from SSMI; winds from NSCAT etc.). It is becoming readily apparent that both GOES and LEO data sets will have to be applied as a "mix" of observations that can address both weather analyses and forecasts produced throughout the National Weather Service, including the national centers and the local forecast offices.
Digital satellite data is now more easily accessible through the infrastructure that supports the NWS field structure. For example, NCEP ingests the following data into their numerical models: 1) the vertical and horizontal distribution of water vapor from LEO sounders; and 2) clear air radiances from LEO sounders. By the end of 1997, the following digital satellite data will also be input into NCEPs models: 1) 3-layer precipitable water from GOES sounders; 2) clear air radiances from GOES sounders; and 3) high density water vapor and cloud-track winds from GOES imagers. Digital satellite products available at the NWS forecast offices include: the low-cloud product, derived from the GOES imager and the lifted index and precipitable water, derived from both the GOES imager and sounder. Furthermore, the local forecast offices have access to quantitative precipitation estimates derived from GOES imager data, GOES sounder data (total precipitable water), and LEO sounder data (precipitable water from microwave sounders); and quantitative estimates of snowfall rates from lake effect snow (LES) bands, based on GOES imager data. The distinction in the use of LEO and GEO data by national centers and field forecast offices is now being blurred by the ready access to the digital data sets produced by both satellite systems.
In 1997, the Earth Science Systems Office requested Goddard Space Flight Center (GSFC) to initiate Advanced Geosynchronous Studies (AGS) for the benefit of both the research and operational communities. A joint NASA-NOAA group was formed to guide these studies.
During the coming decade, AGS will foster advanced geosynchronous instruments and missions in order to:
Currently five instrument/technology areas being emphasized in AGS are:
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This document was composed primarily by Dennis Chesters with suggestions and corrections from (in alphabetical order): Bob Adler, Scott Braun, Franco Einaudi, Jim Gurka, Del Jenstom, Yoram Kaufman, Chris Kummerow, Arthur Hou, Greg Mandt, Dave Martin, Paul Menzel, Marshall Shepherd and Louis Uccellini.