MODIS AIRS and Midlevel Cloud Phase Shaima Nasiri

MODIS, AIRS, and Midlevel Cloud Phase Shaima Nasiri CIMSS/SSEC, UW-Madison Brian Kahn Jet Propulsion Laboratory MURI Hyperspectral Workshop 7 -9 June, 2005 UW-Madison

Outline • Introduce midlevel/potentially mixed phase clouds • MODIS IR phase retrievals for midlevel clouds • Frequency of midlevel clouds • Radiative transfer calculations for MODIS and AIRS for a variety of cloud heights

Midlevel Clouds • Definition: Clouds occurring at a level (height) where water cloud, ice clouds, or mixed-phase clouds could occur (potentially mixed-phase clouds). • Typically between 253 and 263 K • Cloud height depends on latitude and season ~6 km in midlatitudes ~1 km in polar regions (“midlevel” clouds a misnomer here)

ARM M-PACE: 12 October, 2004 Barrow Proteus flight track 2200 UTC Aqua MODIS False Color Phase Image N. Alaska False color cloud phase image: R = 0. 65 µm Ref. , G = 2. 1 µm Ref. , B = 11 µm BT

ARM M-PACE: 12 October, 2004 2200 UTC Aqua MODIS Barrow Slig Uni form N. Alaska htly Bro ken Clo ud False Color Phase Image Clo ud Ice False color cloud phase image: R = 0. 65 µm Ref. , G = 2. 1 µm Ref. , B = 11 µm BT

ARM M-PACE: 12 October, 2004 2200 UTC Aqua MODIS Slig Uni form htly Bro ken Clo ud 11 µm Brightness Temperature Clo ud Ice 245 250 255 260 265 270 MODIS Band 31: 11 µm BT (K)

ARM M-PACE: 12 October, 2004 2200 UTC Aqua MODIS Slig Uni form htly Bro ken Clo ud Infrared Cloud Phase Retrieval Clo ud Ice MODIS IR Cloud Phase at 1 km

ARM M-PACE: 12 October, 2004 2200 UTC Aqua MODIS Infrared Cloud Phase Retrieval Scene is “unknown” because BT[11 µm] is between 253 and 263 K, and BTD[8. 5 -11 µm] is between -1. 0 and 0. 25 K MODIS IR Cloud Phase at 1 km

ARM M-PACE: 12 October, 2004 What are we looking at? AHSRL Circular Depolarization Ratio (%) Aqua MODIS 2200 UTC 11 µm Brightness Temp. Barrow • Lidar shows water cloud with ice precipitating • MODIS 11 µm brightness temperature is around 258 and 259 K N. Alaska

ARM M-PACE: 12 October, 2004 AHSRL Circular Depolarization Ratio (%) • Lidar shows water cloud with ice precipitating • MODIS IR phase classifies scene as “Unknown” Aqua MODIS 2200 UTC IR Phase

ARM M-PACE: 12 October, 2004 AHSRL Circular Depolarization Ratio (%) Question remains: What is the infrared cloud phase? • Lidar shows water cloud with ice precipitating • MODIS IR phase classifies scene as “Unknown”

12 October • Averaged S-HIS spectra with averaged MODIS observations overlaid MODIS Band 32 MODIS Band 31 MODIS Band 29

Modeling • Beginning set of modeling studies to characterize HSR IR cloud sensitivities for the M-PACE case MODIS 8. 5 µm MODIS 12 µm MODIS 11 µm Still need to simulate mixed-phase and overlapping cloud cases Simulations using LBLDIS

How much of a problem are these potentially mixed phase clouds? • Unable to answer the question directly, but we can look at frequency of MODIS IR phase retrievals of ice, water, unknown. • Consider 8 days (and nights) of global Aqua MODIS data from 1 -8 April 2003.

Water Clouds Cloudy pixels classified as liquid water using IR MODIS channels Between 60 S and 60 N, Water Cloud Frequency: 52% Aqua MODIS 1 -8 April, 2003

Ice Clouds Cloudy pixels classified as ice using IR MODIS channels Between 60 S and 60 N, Ice Cloud Frequency: 28% Aqua MODIS 1 -8 April, 2003

Unknown Clouds Cloudy pixels classified as unknown phase using IR MODIS channels Between 60 S and 60 N, Unknown Cloud Frequency: 14% Aqua MODIS 1 -8 April, 2003 Scale is from 0 to 0. 5

Mixed Phase Clouds Cloudy pixels classified as mixed phase using IR MODIS channels (mixed phase should be considered another flavor of unknown) Between 60 S and 60 N, Mixed Cloud Frequency: 6% Aqua MODIS 1 -8 April, 2003 Scale is from 0 to 0. 5

Zonal frequencies of cloud phase (frequency out of all cloudy data) Sum of curves = 1 Mean cloud phase frequencies between 60°S and 60°N Water: 52 % Ice: 28 % Unknown: 14 % Mixed (Unknown): 6 % 20% 10% Aqua MODIS 1 -8 April, 2003

Zonal frequencies of cloud phase (frequency out of all data) Sum of curves = Frequency of cloudiness Mean cloud phase frequencies between 60°S and 60°N Water: 35 % Ice: 18 % Unknown: 9 % Mixed (Unknown): 4 % Aqua MODIS 1 -8 April, 2003

Mid-talk Summary • ~20% of MODIS IR cloud retrievals are classified as “unknown” • Because of the IR phase algorithm, these unknown classifications are likely due to midlevel or potentially mixed-phase clouds

The Question • Can hyperspectral IR data improve our characterization of midlevel/potentially mixed phase clouds?

Brightness Temperature Differences for Water and Ice Clouds Midlatitude winter atmospheric profile Optical thickness at 11 µm MODIS sims from DISORT AIRS sims from CHARTS

Brightness Temperature Differences for Water and Ice Clouds 9 km, T = 226 K 7 km, T = 238 K 3 km, T = 262 K 2 km, T = 265 K 1 km, T = 269 K Optical thickness at 11 µm MODIS sims from DISORT AIRS sims from CHARTS

Brightness Temperature Differences for Water and Ice Clouds =1 K Optical thickness at 11 µm MODIS sims from DISORT AIRS sims from CHARTS

Brightness Temperature Differences for Midlevel Water and Ice Clouds Z 3_water Optical thickness at 11 µm MODIS sims from DISORT AIRS sims from CHARTS

Brightness Temperature Differences for Midlevel Water and Ice Clouds = 0. 5 K Optical thickness at 11 µm MODIS sims from DISORT AIRS sims from CHARTS

Brightness Temperature Differences for Midlevel Water and Ice Clouds AIRS Sims show little sensitivity to water cloud height Optical thickness at 11 µm MODIS sims from DISORT AIRS sims from CHARTS

Summary • ~20% of MODIS IR cloud retrievals are classified as “unknown” • Because of the IR phase algorithm, these unknown classifications are likely due to midlevel or potentially mixed-phase clouds • Simulations shows that hyperspectral IR data can potentially differentiate between ice and water in midlevels (

Future Plans • Continue simulations for • More atmospheric profiles • Overlapping clouds (cirrus over water) • Mixed-phase clouds • Consider different channel combinations • Apply what we learn from simulations to S-HIS and AIRS data from M-PACE • Consider combined hyperspectral and MODIS phase algorithm