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Evaluating a new low-cost radiosonde system for use in adaptive sounding networks (and its implications) Michael Douglas, National Severe Storms Laboratory Norman, OK John Mejia, Desert Research Institute, Reno, Nevada (formerly at OU).
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Evaluating a new low-cost radiosonde system for use in adaptive sounding networks(and its implications)Michael Douglas, National Severe Storms Laboratory Norman, OK John Mejia, Desert Research Institute, Reno, Nevada(formerly at OU)
Original MotivationMuch of my research has involved work with developing countries. These Weather Services usually cannot support dense radiosonde networks...How can these countries/regions carry out effective Numerical Weather Prediction activities?
Very Recent History NSSL Director’s Discretionary Funds allowed for the purchase of a new, low-cost (~$12K) radiosonde system this past year, along with some testing costs.Tests have been carried out in Albuquerque and Norman.
Antenna assembly…simple vertical, not a parabolic tracking antenna, which is much more expensive
iMet-1 radiosonde… 4 “AA” batteries On-off-frequency Switch (info from Company brochure - claims to be “verified”) Radiosondes ~ $175-$200 each in low quantity
Initial results from Sippican-IMET comparisons at Albuquerqueexample of a dual soundingon same balloon
Average of 7 soundings - Sippican RH is ~10% less; T difference less than .1˚C. Winds (GPS) identical.Get pdf of preliminary report from PACS-SONET web site (Google “PACS SONET”) T difference R.H. difference
Wind agreement ... perfect...sort of... 1-sec positions Note: too little attention to wind details... U-component
What are some implications of low-cost radiosonde systems? Can we design a cost-effectiveadaptive sounding network? “Cost effective” implies benefits exceed costs! (Wx Forecasting is fundamentally an economic activity)
Routine (permanent) sounding site costs historically have been high... • Ground station (~$100K) • Inflation shelter for 300-600 gm balloons (~$100K+) • Hydrogen generator (mostly foreign sites) ~$80K • Staffing for 2x daily soundings, high reliability, 7 days/week, 365 days/year (~$50K/year??) Thus, at least $300K to get started, then significant staff effort to keep running. Initial start-up costs limit experimenting with “sounding network design”
Requirements for inexpensiveadaptive sounding network Ground stations must be inexpensive ($10K vrs $100K) Network must be adaptive (say ~120 obs’s/year instead of 730 obs’s/yr) Labor must be local, part-time (pay-by-observation), even at $100 per ob’ this is only ~$15K/year.
There is an upper limit to useful density of radiosonde observations... Balloon ascent rate (~5 m/s) requires ~30-60 minutes to profile troposphere - inadequate for storm-scale forecasting. Time changes and practical limits of synchronizing launches may limit spatial density, perhaps 100 km spatial separation is a practical lower limit. Point of diminishing return rapidly approaches as network density increases - depends on incremental benefits of add’l fcst skill (rarely quantified).
Frequency of adaptive observations • This is motivated by perceived cost-benefit of additional forecast skill... How many days justify additional radiosonde obs’s? • Must quantify ($$$) impact of incremental forecast skill... (meteorology is a science, wx forecasting is an economic activity!) • Must be a fraction of current 2-daily observations to justify “adaptiveness” - like 25% or less of “full time obs’s”
Cost per observation Radiosonde cost (function of quantity purchased) ~ $150 - $200 in low quantities depending on vendor Balloons (size dependent ~$25) Inflation gas (Helium is 3 times H2 cost but safer...) ~ $10 - $30 per balloon Labor cost is controllable...to a point. Pay by observation is most economical. Lets assume $100 per observation for argument. Can use ~$300 per observation as plausible (USA) cost...
Perhaps most obvious example of an adaptive sounding network: for improving hurricane track forecasting Red= routine obs’s, black = adaptive
Cost of this “small” adaptive network… 23 sites across Caribbean Sea region for hurricane track/intensity forecasting Set-up cost ~$500K Annual operation for 60 obs’s/year per site @$300/ob ~ $500K How does this compare with other possible hurricane monitoring and forecast activities?(HRD in 2008 used ~1200 dropsondes and 39 research/operational P-3 flights; these total ~ $2M+)
... for forecasting over Central and Eastern US ~15 sites 60 obs’s/yr ~ $300K/yr
Possible to “easily” reconfigure network for regional focus or evaluation of adaptive strategies (research potential)
Scaling things up a bit:Imagine adaptive network consisting of 100 additional sites across western North America (~4x current density) Set-up cost ~ $2 M, annual cost for 120 obs’s/year per site @ $30K/site: $3 M How does this cost compare with other efforts to improve 12-72 hr fcsts over the central and eastern US? (~60 sites shown)
Problems with adaptive approach • Deciding when to make observations • Maintaining observer proficiency with infrequent obs’s • Reliable 2-way communications is required • Initial purchase of more equipment • Additional gas logistics issues with more sites • Determining whether extra observations have impact on objective and subjective forecasts and the value ($$$) of these impacts...
Pluses of adaptive sounding network… Focus on critical weather forecasts downstream Flexibility in deciding which stations operate on a daily basis Should be great motivator for NWS forecasters - control over special sounding network (“Democratic” decision-making for go-days?) Technology straightforward, little R&D required Could be implemented quickly…
When to make observations? • Must decide on what stations “to activate”. Decision based on: • objective guidance ~ where add’l data will have greatest positive impact on downstream forecast skill... (must identify “priority regions”) • Subjective input - which sectors of economy likely to benefit most from a better forecast... • Blend of objective and subjective tools likely required for go/no-go decisions. Perhaps a blend of SOO input and objective guidance? This area needs work...
Why not just carry out OSSE’s? OSSE’s do cost $$$ (computer and research time) and are model and procedure dependent. OSSE’s cannot evaluate any subjective use of additional soundings and improved analyses at the WFO’s. Why has the current NWS raob network had the same density for the past ~ 50 years? Has it been OSSE-optimized? That is, is the current radiosonde network adjusted to just reach the point of diminishing returns? Not likely... It may actually be less expensive, more convincing, and take considerably less time to to carry out operational trials than to carry out an OSSE.
We are not saying... ... That the current radiosonde network should be replaced by an adaptive network... Daily obs’s are needed for many purposes... Rather, Any adaptive sounding network should complement the current network and be focused on high impact weather events (however those are defined!) This makes it much easier to justify the operational costs
Who should sponsor/organize such an effort? Ought to be NWS...but.... could easily take a decade to program funds... Universities could do it...but which ones...and why should they? Many economic sectors might benefit and could easily fund it... but... why should they if someone else will? NSF-type basic research activity lacks operational component to engage NWS...
Summary: this kind of sounding network is made feasible by introduction of low-cost radiosonde ground stations… UAV-domain? Adaptive sounding domain? AMDAR-domain?
SUMMARY OF MAIN POINTS Low initial cost is key to everything! • With small initial investment there is less pressure to make routine, unsustainable, radiosonde observations • little reluctance to establish more stations, since no cost penalty • Pay-by-observation means low annual labor costs • Logistics are relatively economical (fewer gas transport issues) • Wx prediction focus - smaller balloons - troposphere primarily • But need to quantify the value ($$$) of incremental forecast skill improvement... This may be most cost-effective means to increase short range forecast skill (to 72 hr or thereabouts) in many parts of world - including the USA.
