Development of GEMS Cloud Data Processing Algorithm Yong-Sang Choi 1, Bo-Ram Kim 1, Heeje Cho 2, Myong-Hwan Ahn 1 (Former COMS PI), and Jhoon Kim 3 (GEMS PI) 1 Ewha Womans University, Seoul 2 Seoul National University, Seoul 3 Yonsei University, Seoul

Clouds significantly affect gas/aerosol retrievals! Cloud contamination causes errors in air mass factor, and errors in gas/aerosol retrievals. 2

Comparison of UV cloud products InstrumentWavelength regionProducts GOME-2300 – 800 nmO 3, NO 2, BrO, SO 2, H 2 O, HCHO, and OClO OMI280 – 500 nmO 3, aerosols, surface UV irradiance, NO 2, BrO, SO 2, HCHO, and OClO SCIAMACHY240 – 2380 nmO 3, SO 2, NO 2, BrO, HCHO, OClO, H 2 O, CO, CH 4, CO 2, and clouds TROPOMI270 – 500 nm, 675 – 775 nm, 2305 – 2385 nmO 3, SO 2, NO 2, HCHO, H 2 O, CO and CH 4, and clouds and aerosols 3

a 465 a 470 a 475 a a 490 O 2 -O 2 absorption band (Acarreta, Haan, and Stammes 2004 JGR) Absorption cross-section of the O 2 -O 2 collision complex near 477 nm, based on measurements by Newnham and Ballard [1998] at 283 K (red curve) and 223 K (blue curve). The curve for 253 K (green) was obtained by interpolation. (adopted from OMI ATBD) 4

GEMS cloud algorithm will provide CH and CF by using O 2 -O 2 absorption. Main cloud products: - Cloud height ( z c ) - Effective cloud fraction ( c f ) Main bands: -O 2 -O 2 absorption band (460−490 nm) 5

GEMS cloud algorithm will provide CH and CF by using O 2 -O 2 absorption. Main cloud products: - Cloud height ( z c ) - Effective cloud fraction ( c f ) Main bands: -O 2 -O 2 absorption band (460−490 nm) 6 ISSUE: How to build DOAS and LUT

DOAS-calculated O 2 -O 2 absorption factors (Rc and Ns) are compared with LUT, to get cloud products. LUT variables (7D or 8D) Radiance spectra Solar zenith angle Viewing zenith angle Relative azimuth angle Surface altitude Surface albedo Absorption cross section RcRc NsNs 7 Calculation of Rc and Ns Temperature profile?

DOAS-calculated O 2 -O 2 absorption factors (Rc and Ns) are compared with LUT, to get cloud products. Radiance spectra Solar zenith angle Viewing zenith angle Relative azimuth angle Surface altitude Surface albedo Absorption cross section RcRc NsNs 8 LUT variables (7D or 8D) Temperature profile? Calculation of Rc and Ns ISSUE: How to effectively extract cloud fraction and cloud height from LUT fitting?

C Sequence of cloud height ( z c ) and cloud fraction ( c f ) retrievals zczc OBS DB 9 Cloud height for C f (Albedo = 0.8) Cloud fraction

C Sequence of cloud height ( z c ) and cloud fraction ( c f ) retrievals zczc OBS DB 10 Cloud height for C f (Albedo = 0.8) Cloud fraction zczc

Generation of GEMS synthetic cloud- radiation data TOA UV Radiance (Reflectance) Forward RT simulation Cloud Information 3D NWP model Retrieval Algorithm 11

Data and models Cloud-to-radiance conversion –SCIATRAN (ver 3.1) Cloud properties –WRF model simulation* of –Case: Typhoon Muifa ( 03UTC, August 6, 2011 ) *by Prof. S.-Y. Hong’s team in Yonsei Univ. WRF output  Geometry  Liquid & ice water contents  “Centroid” cloud height 12

Assumptions Standard atmosphere –McLinden climatology Surface albedo –based on WRF’s land category Cloud water droplet size = 10 μm Cloud ice particle size = 50 μm of ‘fractal’ shape 13

A test for c f retrieval R clear clear sky simulation R cloud overcast simulation assuming Lambertian reflector ( A g = 0.8) R meas Synthetic data 14

A test for c f retrieval R clear clear sky simulation R cloud overcast simulation assuming Lambertian reflector ( A g = 0.8) R meas Synthetic data 15

Relation between effective cloud fraction and cloud optical thickness in synthetic data 16 1% of cloud pixels exceed c f value of 1. These clouds are optically thick (τ c ≥ 25), having albedo over 0.8.

Error analysis with synthetic data Errors in cloud height Errors in effective cloud fraction 1%0.06% 10%0.1% 50%0.4% Artificial errors were given to cloud height, and then the sensitivity to errors in effective cloud fraction were tested with our synthetic data. Results show that the sensitivity is fairly small, meaning that cloud height limitedly affects the retrieval accuracy of effective cloud fraction. 17

C Sequence of cloud height ( z c ) and cloud fraction ( c f ) retrievals zczc OBS DB 18 Cloud height for C f (Albedo = 0.8) Cloud fraction zczc Probably Fine How about this?

Error analysis with synthetic data Errors in cloud height Errors in effective cloud fraction 1%0.06% 10%0.1% 50%0.4% Artificial errors were given to cloud height, and then the sensitivity to errors in effective cloud fraction were tested with our synthetic data. Results show that the sensitivity is fairly small, meaning that cloud height limitedly affects the retrieval accuracy of effective cloud fraction. 19

Future study topics and call for In-depth discussion issues in Cloud/aerosol breakout session in GEMS International Science Workshop (October 2013, Korea) Cloud/aerosol effects on various gas retrievals Accuracy of cloud/aerosol products Validation plans for cloud/aerosol products Synthetic cloud-radiation simulators Comparison of algorithms using different bands: O 2 -A, O 2 -B, O 2 -O 2, Raman scattering Etc. 20 Yong-Sang Choi