The impact of space shuttle main engine exhaust on PMCs and implications to trend studies

Transcription

1 The impact of space shuttle main engine exhaust on PMCs and implications to trend studies Michael H. Stevens Naval Research Laboratory Washington, DC 2 nd CAWSES-II TG2 Workshop on Modeling Polar Mesospheric Cloud Trends, Boulder, CO, May

2 Outline 1. Background and Motivation 2. Bright PMCs from the Final Space Shuttle Launch 3. The SBUV long-term PMC variations 4. Relevance of Space Traffic to SBUV PMC Time Series 5. Summary

3 Background and Motivation Reported PMC albedo and frequency trends at 70 N now average less than 4%/decade since One shuttle main engine H 2 O exhaust plume can produce 10-20% of PMCs near 70 latitude for one Arctic or Antarctic season. Here we take inventory of all space traffic H 2 O exhaust since 1979 and compare against PMC mass observed by SBUV during that time. Can space traffic account for either a PMC trend or contribute to the interannual variability of PMCs?

4 PMCs from Shuttle Exhaust in the Arctic and Antarctic

5 Seven Cases of Shuttle Exhaust Forming PMCs Shuttle Launch Date Reference STS-66 3 Nov 1994 Stevens et al. (2002) STS-85 7 Aug 1997 Stevens et al. (2003) STS Jul 1999 Stevens et al. (2005a) STS Jan 2003 Stevens et al. (2005b) STS Jul 2005 Collins et al. (2009) STS Aug 2007 Kelley et al. (2009; 2010) STS Jul 2011 Stevens et al. (submitted)

6 PMCs from the Final Space Shuttle Launch

7 Ascent for Final Launch Similar to all Previous Shuttles 350 t of H2O injected between km

8 Odin Sub-Millimeter Radiometer: 99 km H2O Small symbols are scan locations, large symbols 3σ plume detections. Data are assembled in 12-hour increments. Expansion of the plume much faster than by molecular diffusion alone.

9 CIPS PMC Observations one day after STS-135 Launch CIPS Albedos: 9 July 2011 CIPS Bright Clouds NH 2011 A PMCs about ten times brighter than usual at 12:04 UT over Scandanvia 20 hrs and 29 min after launch. These PMCs are the brightest 0.01% of 2011 PMCs from N. Red arrows indicate launches worldwide

10 RMR Lidar Observations at 69 N one day after Launch 532 nm Volume Backscatter Coefficient (β) Climatology of β int 9 July 2011 Unusually bright cloud at 12:14 UT, 21 hrs after STS-135 launch Brighter than 99.98% of all NLCs observed since 1997 These observations suggest that the brightest PMCs are from shuttle exhaust but SBUV only measures the brightest PMCs what part of the SBUV record can be explained by space traffic?...

11 The SBUV long-term PMC variations

12 SBUV PMC Observations are Over Many Local Times and SSAs DeLand et al. [2007] Between 0930 and 1400 LT there is an uninterrupted time series of PMC data Limiting analysis to these data avoids adjustments for LT and the variation of sensitivity due to the solar scattering angle, which is higher near the terminator.

13 Local Times and SSA Nearly Constant for These Selected Data Expands analysis of Stevens et al. [2007] from 2005 through When more than one satellite available, data averaged together for that year.

14 Long Term Variation of SBUV Albedo and Ice Water Content Small albedo trend is not statistically significant (-10 to 20 DRS). Shaded area represents uncertainty in the prescribed size distribution.

15 Long Term Variation of SBUV Frequency and PMC Mass Neither small frequency trend or small PMC mass trend is statistically significant. Large interannual variability exists in both time series.

16 Relevance of Space Traffic to SBUV PMC Time Series

17 Approach Inventory all space traffic exhaust injected into the upper atmosphere since SBUV PMC time series began in Compare total mass injected to total mass observed by SBUV during each PMC season (70 ± 2.5 N). Can space traffic exhaust help explain the interannual variability of PMCs? Can space traffic exhaust account for an inferred PMC trend since 1979?

18 H 2 O Exhaust from Orbital Launch Vehicles: Launch Vehicle Total Fuel* (t) Total H 2 O Exhaust km (t) Total Launches** Total H 2 O* (t) Space Shuttle Soyuz/Molniya Ariane Proton Delta II *Not including boosters **Between -18 and 28 DRS Sources: American Institute of Aeronautics and Astronautics (AIAA), Atmospheric Effects of Chemical Rocket Propulsion, 52 pp., New York, Isakowitz, S.J., J.P. Hopkins, Jr. and J.B. Hopkins (1999), International Reference Guide to 664 Space Launch Systems (3rd ed.), AIAA, Reston, VA.

19 Example: Ariane 5 Launch Trajectory 102 t H2O km Source: Ariane 5 Users Manual

20 Annual Mass of Space Traffic Exhaust Shuttles dominate the H 2 O inventory, w/ minima in mid 80 s and mid 00 s CO 2 and CO are other major species released into upper atmosphere

21 Interannual Variability of PMCs vs. Space Traffic H2O Avg. PMC mass: 80 t/yr Avg H2O exhaust: 230 t/yr (90 t/yr w/out shuttle) Note: Loss by photodissociation is 30-60% after 3-4 days [Stevens et al., 2003; Stevens et al., 2005]. Still plenty of H 2 O available to drive interannual variability of PMCs.

22 Summary There are now 7 documented cases of space shuttle main engine exhaust forming PMCs: 6 in the Arctic and 1 in the Antarctic. Evidence from the final launch of the shuttle in July, 2011 indicates that the brightest PMCs are formed from space shuttle exhaust. The amount of H 2 O deposited into the upper atmosphere ( km) by shuttle and other space traffic from is about four times larger than reported SBUV PMC mass at 70±2.5 N (-12 to 18 DRS). There is enough space traffic H 2 O to account for interannual variability and decadal-scale trends in PMCs at 70 N.

23 Compelling Needs Amplitudes and phases of tides and planetary waves at all northern latitudes between km near solstice. Comparison with launch latitudes and local times. Better estimates of horizontal diffusion of plume, which is faster than predicted by molecular diffusion alone. Better estimates of vertical diffusion of plume, which is suggested as a means to bring the plume water vapor from the lower thermosphere ( km) to the upper mesosphere (85-90 km).