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Benefits & Impact

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WIGOS Technical Report 2015-1

A report to the World Meteorological Organization on the

 

Impact and benefits of AMDAR temperature, wind and moisture observations in operational weather forecasting

Authors: Ralph Alvin Petersen, Lee Cronce, Richard Mamrosh and Randy Baker

Download from WMO Library (20MB)

Abstract

Summary Excerpts

   Summary of impacts of AMDAR Temperature and Wind Reports

   Summary of AMDAR Water Vapor Observation Assessments

   Summary and Recommendations

 

Abstract

This report reviews the impact of AMDAR observations on operational NWP forecasts at both regional and global scales that support national and local weather forecast offices across the globe. Over the past three decades, data collected from commercial aircraft have helped reduce flight level wind/temperature forecast errors by nearly 50%. Improvements are largest in 3-48 h forecasts and in regions where the automated reports 1) are most numerous, 2) cover a broad area, and 3) are available at multiple levels, e.g., made during aircraft ascent and descent. Improvements in weather forecasts due to these data have already had major impacts on a variety of aspects of airline operations, ranging from fuel savings from improved wind/temperature forecasts used in flight planning to passenger comfort and safety due to better awareness of en-route and near-terminal weather hazards. Aircraft wind/temperature observations now constitute the 3rd most important data set for global NWP and, in areas of ample reports, have become the single most important data set for use in shorter-term, regional NWP applications. Automated aircraft reports provide the most cost effective data source for improving NWP, being more than five times more cost effective than any other major-impact observing system. They also present an economical alternative for obtaining tropospheric profiles both in areas of diminishing conventional observation and as a supplement to existing data sets, both in time and space.

Although wind and temperature observations provided from commercial aircraft have been shown to improve operational numerical weather prediction (NWP) on global and regional scales, the quality and potential importance of newly available moisture observations are less well recognized. Because moisture changes often occur at much smaller scales than wind and temperature variations, these temporally and spatially frequent moisture observations can have exceptionally large impacts on forecasts of disruptive weather events and could help offset the dwindling number of global moisture observations. Currently, more than 115 aircraft-based Water Vapor Sensing Systems (WVSS-II) provide specific humidity observations en-route and during takeoff/landing, with 112 units operating in the US and 3 in Europe. Results of a series of assessments comparing data from WVSS-II sensors initially installed on twenty-five UPS Boeing 757 aircraft with co-located RAOBs show agreement to within 0.5 g/kg, with minimal biases. Inter-comparisons of observations made amongst nearby aircraft agree to better than 0.2 g/kg. The combined results suggest that the WVSS-II measurements are at least as accurate as water vapor observations from high-quality RAOBs. Information regarding observed spatial and temporal moisture variability could be important in optimizing the use of these observations in future mesoscale assimilation systems. Forecasts of disruptive weather events made by NWS and airline forecasters demonstrate the benefits obtained from combined temperature/moisture/wind profiles acquired during aircraft ascents and descents. Finally, a review of initial NWP impact studies shows that WVSS-II reports obtained throughout the day have greater influence than twice-daily RAOBs on 1-2 day forecasts over the US.

Summary Excerpts

Summary of impacts of AMDAR Temperature and Wind Reports:

Tests conducted by numerous NWP centers for over 25 years have demonstrated that high-quality and high-frequency AMDAR temperature and wind observations increase the skill of forecasts at both regional and global scales and for both short- and medium range forecasts. Results show that aircraft data taken at cruise levels and during ascent/descent provide important information for improving forecasts, both in terms of long-term average performance and for individual events. Although global, ‘all-weather’ satellite microwave observations have the largest average influence on medium-range global forecasting system (especially in the SH), AMDAR observations have become recognized as a critical component of these systems around the world. Aircraft observations rank 3rd in importance globally (especially in the NH) and contribute between 10-15% to 24-h forecast skill improvement, with impacts extending to 48 hours and beyond. In areas with denser data coverage aloft and abundant ascent/descent reports, they have become the single most important data set for use in shorter-range, regional NWP applications.

A unique feature of AMDAR reports is that they provide both temperature and wind data at the same locations and in profiles made during ascent/descent, thereby furnishing explicit two-dimensional information on baroclinic adjustments needed in DA systems. Because the data are available continuously along flight routes, the observations also provide information about gradients of wind and temperature near high-energy jet stream regions. The availability of multiple reports along flight routes is also important for cross-validation and QC (WMO 2014).

Results presented here attest to 1) the quality of the data, 2) the importance of the reports made both as profiles during ascent/descent and at cruise level near the major reservoir of energy in the atmosphere and 3) the ease of use of the wind and bias-corrected temperature information in DA systems. Additional experiments are needed to understand more fully how temperature and wind gradient information that can be derived from cruise-level AMDAR reports may contribute to the enhanced importance of AMDAR data relative to other, more costly data sets.

Summary of AMDAR Water Vapor Observation Assessments:

Tests conducted by numerous NWP centers over the past decade have concentrated on assessing the impact of AMDAR temperature and wind observations on the skill of regional and global NWP systems. Results show that aircraft data taken en-route and during ascent/descent provide important information for improving forecasts, both for individual events and for long-term performance. These tests, however, did not take into account the additional improvements that can occur from the new moisture observing systems being deployed as part of the global AMDAR enhancement effort.

Evaluations of new WVSS-II moisture observing systems being deployed on aircraft in the US show that WVSS-II observations:

1) Provide excellent quality horizontally and vertically, even across sharp inversions,
2) Agree with co-located RAOBs to within 0.6 g/kg, with minimal biases (approximately 0.15 g/kg), and
3) Display consistency between observations from different aircraft of at least 0.2 g/kg, indicating that WVSS-II observations perform as well as high-quality RAOBs.

Forecasters have been able to readily incorporate WVSS-II reports (along with AMDAR temperature and wind profiles) into their forecasting process. The availability of the data throughout the day has proven valuable in improving local, short-range forecasts of a number of high-impact weather phenomena, ranging from forecasts of fog and ceiling height to determining precipitation type and improving severe weather outlooks. Finally, a review of initial NWP
impact studies shows that WVSS-II reports obtained throughout the day have greater influence than twice-daily RAOBs on 1-2 day forecasts over the US.

The volume of WVSS-II data available over the US has recently grown to a level that can support initial data impact tests in NWP models. Initial results using SH observations from the expanded fleet of WVSS-II equipped aircraft over the US have shown short-range forecast impacts larger than from any other moisture observations, including twice-daily RAOBs. Humidity forecast improvements like these are essential to enhance prediction of both the timing and location of precipitation events.

Summary and Recommendations:

The long-term, consistently positive impacts of automated aircraft reports on regional and global operational NWP presented here provide ample evidence that the collaborative effort between airlines and National Meteorological Services to improve access to and use of automated wind and temperature reports has benefited both the data providers and other users of the other products issued by NWP centers and forecasters using these data. AMDAR growth has occurred chiefly over developed countries whereas, for developing and least-developed countries, the progress in implementation has lagged and is now well behind. Because improvements attributable to AMDAR observations have been concentrated in areas of highest data availability, greater improvements can be expected in other more data sparse regions as the spatial and temporal coverage of AMDAR reports increases globally. As a means of fostering further AMDAR expansion, cooperative means (including possible cost sharing opportunities) should be developed both to continue expanding the AMDAR observing network into areas not currently covered adequately and to increase the number of aircraft providing data, especially over data sparse regions of the globe. This should include establishing dedicated efforts at regional and global NWP centers to continue evaluation of the impact and cost effectiveness of all observing systems components, with the goal of promoting rapid expansion of those systems that have both high value and low cost.

Although the improvements attributable to AMDAR observations have been concentrated in areas of highest data availability, similar improvements are expected in other areas as the spatial and temporal coverage of the reports increases globally, especially if water vapor measurements are included. This will
be particularly important both in areas where the continuation of upper-air observing programs are
under budgetary threat and in forecast situations where additional observations are needed to fill the time and space gaps between once- or twice-daily RAOB launches.

Based on these findings, it is recommended that cooperative means, including possible cost-sharing opportunities, be developed simultaneously 1) to expand the AMDAR observing network into areas not currently covered adequately and 2) to increase the number of aircraft providing humidity information.

Both of these recommendations are financially and logistically viable. AMDAR observations are extremely cost effective, currently contributing only about 0.25% of the expense of the global observing system (Eyre and Reid 2014), with temperature/moisture/wind profiles typically costing less than 5% of a full ROAB launch. Because the AMDAR observing system can be attached to commercial aircraft from many airlines that already have well-established air-to-ground communications systems, the systems can be implemented with only minor impact on other operational and engineering resources available at local meteorological services.

It should be recognized that AMDAR reports will not meet all balloon-borne observing requirements (in particular, data in and above the stratosphere needed for both weather and climate purposes). However, the availability of high-quality tropospheric information over land at space and time resolutions not affordable using conventional observing systems offers a unique opportunity for improving weather forecasts across the globe, including terminal and weather hazard forecasts benefiting airlines. Improvements in safety-related forecasts used for aircraft and airspace operations could be enhanced further through incorporation of additional turbulence and icing observations in future AMDAR reports.

For more information on the benefits and impact of AMDAR data see the AMDAR/Resources/Programme Development area.





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