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 False color cloud phase image: R = 0.65 µm Ref., G = 2.1 µm Ref., B = 11 µm BT 2200 UTC Aqua MODIS False Color Phase Image Barrow N. Alaska Proteus flight track

ARM M-PACE: 12 October, 2004 False color cloud phase image: R = 0.65 µm Ref., G = 2.1 µm Ref., B = 11 µm BT 2200 UTC Aqua MODIS False Color Phase Image Barrow N. Alaska Uniform Cloud Slightly Broken Cloud Ice

ARM M-PACE: 12 October, 2004 MODIS Band 31: 11 µm BT (K) 2200 UTC Aqua MODIS 11 µm Brightness Temperature Uniform Cloud Slightly Broken Cloud Ice

ARM M-PACE: 12 October, 2004 MODIS IR Cloud Phase at 1 km 2200 UTC Aqua MODIS Infrared Cloud Phase Retrieval Uniform Cloud Slightly Broken Cloud Ice

ARM M-PACE: 12 October, 2004 MODIS IR Cloud Phase at 1 km 2200 UTC Aqua MODIS Infrared Cloud Phase Retrieval Scene is “unknown” because BT[11 µm] is between 253 and 263 K, and BTD[ µm] is between -1.0 and 0.25 K

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

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

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

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 Simulations using LBLDIS MODIS 12 µm MODIS 11 µm MODIS 8.5 µm Still need to simulate mixed-phase and overlapping cloud cases

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.

Aqua MODIS 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%

Ice Clouds Cloudy pixels classified as ice using IR MODIS channels Aqua MODIS 1-8 April, 2003 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 Scale is from 0 to 0.5 Between 60 S and 60 N, Unknown Cloud Frequency: 14%

Aqua MODIS 1-8 April, 2003 Mixed Phase Clouds Cloudy pixels classified as mixed phase using IR MODIS channels (mixed phase should be considered another flavor of unknown) Scale is from 0 to 0.5 Between 60 S and 60 N, Mixed Cloud Frequency: 6%

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

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

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 Optical thickness at 11 µm MODIS sims from DISORTAIRS sims from CHARTS Midlatitude winter atmospheric profile

Brightness Temperature Differences for Water and Ice Clouds Optical thickness at 11 µm MODIS sims from DISORTAIRS sims from CHARTS 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

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

Brightness Temperature Differences for Midlevel Water and Ice Clouds Optical thickness at 11 µm MODIS sims from DISORTAIRS sims from CHARTS Z3_water

Brightness Temperature Differences for Midlevel Water and Ice Clouds Optical thickness at 11 µm MODIS sims from DISORTAIRS sims from CHARTS  = 0.5 K

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

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