Reconstructing the GPS Refractivity Profiles inside the Atmospheric Boundary Layer with MODIS Cloud top temperature over Subtropical Eastern Oceans

Transcription

1 Reconstructing the GPS Refractivity Profiles inside the Atmospheric Boundary Layer with MODIS Cloud top temperature over Subtropical Eastern Oceans Feiqin Xie Texas A&M University Corpus Christi, TX Coauthors: C. O. Ao, J. F. Turk, A.J. Mannucci (JPL); E. R. Kursinski (Broad Reach Engineering) and D. L. Wu (GSFC) Acknowledgement: NOAA NESDIS (NA08NES ); NASA SMD NNH06ZDA001N GNSS, 2006, TAMUCC for Travel Support; JPL/UCAR GPS operational teams. Sixth FORMOSAT-3/COSMIC Data Users' Workshop (October 30, 2012)

2 Southeast Pacific Ocean Natural Laboratory for ABL study Radiosonde COSMIC Courtesy of Drs. Rob Wood (Univ. of Washington) S. de Szoeke (Oregon State Univ.) for radiosonde soundings Xie. et al., ACP, 2012

3 Near coincident Case over Southeast Pacific Radiosonde/COSMIC/ECMWF Systematic N-bias is caused by super-refraction/ducting. The inversion-base height is consistent with Cloud-top-height)

4 N-bias - Non-unique Abel-inversion problem Best Solution Sounding Family Standard Retrieval Assimilating bending angle does NOT solve N-bias problem The biased (/-) model refractivity profiles (pink) CAN T be distinguished from the forward simulated bending in the presence of duct. Xie et al., JTECH, 2006

5 Systematic negative N bias over subtropical eastern oceans inside ABL (Refr_GPSRO - Refr_ECMWF) / Refr_ECMWF * 100 Xie et al., GRL 2010

6 Maximum Refractivity Gradient (MRG) vs. N Bias MRG COSMIC MRG ECMWF COSMIC ECMWF N-Bias at 0.8 km (RO-ECMWF)/ECMWF (%) 20oS Cross Section Radiosonde Xie et al., ACP (2012)

7 Reconstruction with Independent Constraint Surface constraint o δtsfc (1k), δpsfc (1mb), δqsfc (10%) δnsfc = % = ~2.5% o Pros: Easy to apply by using global analysis or simple qsfc model o Cons: lack of accurate water vapor constraint near surface. Inversion base constraint: CTT (Saturated at Cloud-top) o δtctt (1K) δqsat_ct (7%) δnct (0.7%) o δpct (1mb) δnct (0.1%) o Pros: Most effective constraint due to the maximum N-bias near inversion base (up to ~16%). Cons: Availability of CTT from MODIS (Solution: GOES CTT); Limited to overcast region. o

8 Near coincident COSMIC vs. CALIPSO (<18min apart) 18S COSMIC/RO 20S 22S 24S 26S CloudSat CALIPSO Track GOES 78W 76W 74 72W

9 MODIS 10S 10S 15S 15S Cloud Fraction 20S COSMIC/RO 20S 25S 25S 90W 85W 80 75W 70W 65W

10 MODIS 10S 10S 15S 15S Cloud-top Temperature 20S COSMIC/RO 20S The overcast region with most accurate and 25S homogeneous CTT from MODIS 90W 85W 80 75W 70W 65W 25S

11 ABL Reconstruction (CTT) Near coincident COSMIC vs. CALIPSO (<18min apart) 18S COSMIC/RO 20S 22S CTT_MODIS = C N_MODIS = (N-unit) CALIPSO 24S 26S MODIS GOES 78W 76W 74 72W

12 Conclusions Systematic biases in the GPS RO refractivity are mainly caused by super refraction (or ducting) over subtropical eastern oceans. The MODIS Cloud Top Temperature can be used as an independent physical constraint to recover ABL refractivity. Potential usage of GOES CTT observations will allow the maximum benefit of reconstructing biased RO refractivity. Assimilating bending angle does NOT avoid/solve the non unique inversion problem that causes the N bias. The next generation RO receiver (e.g.,trig on COSMIC II) with higher SNR will allow better measurement inside the ABL, but the N bias still need to be solved.

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14 Backup Slides

15 MODIS 10S 10S 15S 15S COSMIC/RO 20S 20S Cloud-top Pressure 25S 25S 90W 85W 80 75W 70W 65W

16 Near coincident COSMIC vs. CALIPSO (<18min apart) GOES Both the GPS bending and refractivity gradient show a higher ABL (~1km) than ECMWF model analysis (~0.9km)

17 Acknowledgement NOAA NESDIS (NA08NES ) support for the super refraction research. NASA grant through JPL/JIFRESSE UCLA. JPL GPS operational team: B. Iijima, M. Pestanal, T. Meehan and L. E. Young for COSMIC RO soundings. ECMWF for high resolution analysis data; Drs. Rob Wood (Univ. of Washington) S. de Szoeke (Oregon State Univ.) for radiosonde soundings.

18 Cloud Top Height ~1km (21.7S, 74.1W) CALIPSO (lidar) 0 30S 90W [km] Lat Lon [km] 45W

19 Reconstruction Hypothesis Hypothesis-I: the CTH corresponds to the height of inversion base for stratus or stratocumulus; Hypothesis-II: the atmosphere at the cloud top is saturated; Hypothesis-III: the CTH is 100-m below the ABL height detected from RO soundings in Step-II, i.e., CTH = h_abl 100 [m] (de Szoeke et al., 2009); Hypothesis-IV: the refractivity structures inside ducting layer are composed of two linear segments (Xie et al., 2006).

20 Near coincident Case over Southeast Pacific Radiosonde/COSMIC/ECMWF 1-m smoothed Atmospheric200-m desert over the Earth s refrigerator The sharp temperature and moisture gradient at ABL top results in a large bending in GPS signal

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22 N/T/RH Relation 1 deg K 5% RH 10% RH Xie et al., TGRS, 2008