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Comparison of Airborne Water Vapor Lidar Observations with
Comparison of Airborne Water Vapor Lidar Observations with ECMWF Analyses and first Assimilation Experiments Christoph Kiemle, H. Flentje, E. Holm, A. Fix, A. Dörnbrack, G. Ehret 7. ISTP, Boulder, 13. June 2006 Overview • Water vapor lidar system onboard DLR Falcon aircraft; • long-range intercontinental cross sections during transfer flights from Germany to different remote campaign locations: Brazil (2004): across equatorial Atlantic Ocean; Australia (2005): midlat., subtropical, tropical climate regimes; USA (2002): across North Atlantic storm track region. • First 4D-VAR assimilation of Lidar observations into ECMWF operational NWP model. Institut für Physik der Atmosphäre H2O Differential Absorption Lidar on the Falcon Aircraft Key features: stabilized OPO, 920 - 945 nm, 100 Hz, 2 W, sp > 99% H2O-DIAL inside the Falcon Institut für Physik der Atmosphäre Institut für Physik der Atmosphäre Transfers to/from Brazil Jan./March 2004 Oberpfaffenhofen Sevilla 31 Jan - 2 Feb 04⇓ Sal ⇑ 14 - 15 Mar 04 Equator F. de Noronha Recife Institut für Physik der Atmosphäre Range: Nadir: down to ground Zenith: ≈ 2 - 6 km above flight level Channels: H2O BSR 1064, 935, 532 nm Depol 1064, 532 nm Transfer Brazil - Germany on 14.3.2004: Met. Situation • Trough along NW-African coast (Cyclone over Morocco) • Azores high dominates central Atlantic - nearly cloud free • Sharp water vapor gradient delimiting tropics near 10°N at 500hPa Trade winds ITCZ Meteosat 8 Institut für Physik der Atmosphäre Azores high H2O and Geopot @ 500 hPa from T511/L60 ECMWF analysis Transfer Brazil - Germany: Water Vapor Hadley Circulation • Humid layer slopes from 9 km near Eq. to 4 km at 15°N • 2 g/kg H2O up to 9 km • Outflow above 8 km till 15°N • 30°N: UT/LS air intrudes down to the PBL • H2O < 0.1 g/kg in 2 km • Dry layer advected from the N-American continent with H2O < 0.1 g/kg Institut für Physik der Atmosphäre • Upsliding moister air mass subsides near the intrusion Transfer Brazil - Germany: ECMWF Trajectories 300 hPa 600 hPa temperature (K) T511/L60 ECMWF analyses Institut für Physik der Atmosphäre Water Vapor Data Quality Systematic • Water vapour absorption line cross section (5 % estimated) errors ( ~ 5%) • Laser spectral impurity (1 - 2 %) • Atmospheric temperature uncertainty (1 %) • Rayleigh-Doppler absorption line broadening (< 1.5 %) Random error controlled by spatial resolution: σstat = Stdev/Mean = 1/SNR Δz=700m Δx=2600m Δz=500m Δx=3400m 5% 7% 33% 5% 43% 8% 7% Institut für Physik der Atmosphäre ≈ 0-2 % from natural variability Comparison of individual profiles Institut für Physik der Atmosphäre DIAL water vapor observation ECMWF water vapor profile Comparison of individual profiles Institut für Physik der Atmosphäre DIAL water vapor observation ECMWF water vapor profile Spec. Hum. Comparison between DIAL and ECMWF T511/L60 operational analysis, interpolated in space and time to flight path. Institut für Physik der Atmosphäre Comparison of H2O from DIAL and ECMWF • ECMWF too humid in UT • Median Difference (Bias) ≈ 8% • Larger differences due to interpolation limits Institut für Physik der Atmosphäre Submitted to JGR, 2005 Transfer Flights to/from Australia, Nov./Dec. 2005 Oberpfaffenhofen Larnaca Dubai Hyderabad Bangkok Darwin Institut für Physik der Atmosphäre Focus on Transect Hyderabad - Dubai Oberpfaffenhofen Larnaca Dubai Hyderabad Bangkok Darwin Institut für Physik der Atmosphäre Lidar ECMWF Diffs Dubai Institut für Physik der Atmosphäre Hyderabad water vapor volume mixing ratio (10-6) Lidar Measurements and ECMWF Analyses Dubai Hyderabad water vapor volume mixing ratio (10-6) T799/L91 operational analysis, interpolated in space and time to flight path. Institut für Physik der Atmosphäre Transfer Flights to/from IHOP, May/June 2002 Institut für Physik der Atmosphäre Tropospheric Cross Section from H2O DIAL (ppmm) 0045 UT 60° 0255 UT 0530 UT 50° 40° 0830 UT 1110 UT 0645 UT 15 May 2002 Institut für Physik der Atmosphäre 2230 UT 14 May 2002 13 May 2002 2000 UT First 4D-VAR Assimilation of H2O DIAL data at ECMWF Significant improvement of 12h-forecast of H2O column of 5 - 20% Tropopause height Height WV mixing ratio [g/kg] Lidar T511 outer loops and T95 - T159 inner loops Institut für Physik der Atmosphäre rel. change of total WV error ECMWF lat. long. New Airborne 4-wavelengths H2O DIAL 3 online, 1 offline for LT-LS profiling Data Acquisition (hidden) Wavelength Control Optical Filter Box LCD-Screen Keyboard Pump Lasers 48 cm Telescope OPOs Institut für Physik der Atmosphäre Expected Performance relative to present H2O-DIAL Example: Sounding of the tropical cold point region (looking upward) 9 6-times higher average output power at same volume and only 10% higher weight 9 3-times higher single pulse energy 9 1,8-times larger telescope area 9 2-times less detector noise First test flight: Dec. 2006 Institut für Physik der Atmosphäre Conclusion: Long-range airborne lidar observations • Stronger dynamical activity at mid-lat.: quasi continuous STE; • smaller scales and larger H2O gradients at mid-lat.; • high-reaching humidity in the tropics up to UT; • weak cyclogenesis and no intrusions over central Atlantic; • signature of Hadley circulation observed in water vapor. Conclusion: Comparisons with ECMWF analyses • Qualitatively fair agreement, model reproduces dynamical structures; • deviations due to small displacements of structures and finite temporal / spatial resolution; • better skill of ECMWF in (sub-) tropics due to larger scales. Institut für Physik der Atmosphäre Conclusion: 4D-VAR assimilation of lidar observations • Positive impact on 12-h operational forecast despite few lidar data: encouraging results. Outlook • Assimilation experiments with lidar data from longrange transects to Brazil and Australia. Institut für Physik der Atmosphäre
