Bryan A. Baum 1, Ping Yang 2, Andrew J. Heymsfield 3, and Sarah Thomas 4 1 NASA Langley Research Center, Hampton, VA 2 Texas A&M University, College Station, TX 3 National Center for Atmospheric Research, Boulder, CO 4 Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madison Development of Ice Cloud Scattering Models from Polar, Midlatitude, and Tropical In-situ Measurements Development of Ice Cloud Scattering Models from Polar, Midlatitude, and Tropical In-situ Measurements

1. Derive a set of microphysical models that better represent the range of naturally occurring ice clouds. 2. Build a set of multispectral scattering models for MODIS and other imagers. 3. Suggest two approaches for validation of the new models. Goals of the Work

Version 1Version 2Version 3 Particle Size Distributions (PSD) 12 PSDs discretized to 5 size bins, very crude; Some models are similar to others 3 Averaged PSDs discretized to 27 size bins, based on our evaluation of Heymsfield’s data Based on Gamma distribution fits to PSDs; >30 bins (more bins for large sizes) Microphysical Data Source FIRE-I, FIRE-II, and older; difficult to trace back to source FIRE-I, FIRE-II, ARMFIRE, ARM, TRMM, SHEBA, CRYSTAL Habit Distributions and Habits Exactly the same for each model; based on plates, solid/hollow columns, 2D bullet rosettes, aggregrates Varies by model; based on plates, solid/hollow columns, 2D bullet rosettes, aggregrates Varies by model; New habits: droxtals, 3D bullet rosettes Scattering models Scattering models computed in 1997; Based on Terra SRF Scattering models computed ; spectral resolution based on Terra SRFs Recompute scattering libraries with higher resolution in particle size and wavelength; add new parameters such as Qe; Dm Limitations Models based solely on midlatitude cirrus; not readily adaptable to global analyses Analysis of size spectra is complex; based solely on midlatitude cirrus TBD

MODIS Version 1 Cirrus Microphysical Models Note: 5 size bins; fixed habit percentage used in all models MODIS Version 1 Cirrus Microphysical Models Note: 5 size bins; fixed habit percentage used in all models Max length < 70  m 50% bullet rosettes 25% hexagonal plates 25% hollow columns Max length > 70  m 30% bullet rosettes 20% hexagonal plates 20% hollow columns 30% aggregates Baum, B. A., D. P. Kratz, P. Yang, S. Ou, Y. Hu, P. F. Soulen, and S-C. Tsay, 2000a: Remote sensing of cloud properties using MODIS Airborne Simulator imagery during SUCCESS. I. Data and models. J. Geophys. Res., 105, 11,767-11,780.

Validation Approach #1 ATSR-2 Measurement Residual Analysis Testing the single-scattering properties of MODIS Version 1 cirrus models between scattering angles of 57 o and 170 o Dr. Anthony J. Baran and Dr S. Havemann Met Office, UK Channels located at 0.55, 0.66, 0.87, 1.6, 3.7, 10.8, and 11.9  m Cloud height determined by parallax technique Cloud properties inferred by optimal estimation method Perform forward calculations, then minimize difference between measurements and simulations

ATSR-2 Image at 0.87  m 21 July, 1996; Latitude o ; Longitude o ATSR-2 Image at 0.87  m 21 July, 1996; Latitude o ; Longitude o

ATSR-2 Residual Results 21 July, 1996; Latitude o ; Longitude o Scattering angle: o (forward) ATSR-2 Residual Results 21 July, 1996; Latitude o ; Longitude o Scattering angle: o (forward)

ATSR-2 Residual Results 21 July, 1996; Latitude o ; Longitude o ; Scattering angle: o (nadir) ATSR-2 Residual Results 21 July, 1996; Latitude o ; Longitude o ; Scattering angle: o (nadir)

False Color Image R: 0.65  m reflectance G: 0.87  m reflectance B: 1.6  m reflectance ATSR-2 Image 23 July, 1996; Latitude o ; Longitude o ATSR-2 Image 23 July, 1996; Latitude o ; Longitude o

ATSR-2 Residual Results 23 July, 1996; Latitude o ; Longitude o Scattering angle: o (forward) ATSR-2 Residual Results 23 July, 1996; Latitude o ; Longitude o Scattering angle: o (forward)

ATSR-2 Residual Results 23 July, 1996; Latitude o ; Longitude o Scattering angle: o (nadir) ATSR-2 Residual Results 23 July, 1996; Latitude o ; Longitude o Scattering angle: o (nadir)

Replicator Ice Crystal Profiles from FIRE Cirrus II Campaign

Version 1Version 2Version 3 Particle Size Distributions (PSD) 12 PSDs discretized to 5 size bins, very crude 3 Averaged PSDs discretized to 27 size bins, based on our evaluation of Heymsfield’s data Based on Gamma distribution fits to PSDs; >30 bins (more bins for large sizes) Microphysical Data Source FIRE-I, FIRE-II, and older; difficult to trace back to source FIRE-I, FIRE-II, ARMFIRE, ARM, TRMM, SHEBA, CRYSTAL Habit Distributions and Habits Exactly the same for each model; based on plates, solid/hollow columns, 2D bullet rosettes, aggregrates Varies by model; based on plates, solid/hollow columns, 2D bullet rosettes, aggregrates Varies by model; New habits: droxtals, 3D bullet rosettes Scattering models Scattering models computed in 1997; Based on Terra SRF Scattering models computed ; spectral resolution based on Terra SRFs Recompute scattering libraries with higher resolution in particle size and wavelength; add new parameters such as Qe; Dm Limitations Models based solely on midlatitude cirrus; not readily adaptable to global analyses Analysis of size spectra is complex; based solely on midlatitude cirrus TBD

Cirrus Size Distributions Based on In-situ Data From Midlatitude Cirrus Version 2: Scattering properties available for 27 size bins

MODIS - Current Set of Cirrus Models (Version 1) Max length < 70  m 50% bullet rosettes 25% hexagonal plates 25% hollow columns Max length > 70  m 30% bullet rosettes 20% hexagonal plates 20% hollow columns 30% aggregates Cirrus Habit Percentages Based on In-situ Data From Midlatitude Cirrus FIRE-II - avg. of 3 cases (cold cirrus) Max length < 100  m 35% bullet rosettes 46% hexagonal plates 16% hollow columns 3% aggregates Max length > 100  m 38% bullet rosettes 0% hexagonal plates 22% hollow columns 40% aggregates FIRE-I - avg. of 5 cases (warm cirrus) Max length < 150  m 37% bullet rosettes 0% hexagonal plates 63% hollow columns 0% aggregates Max length > 150  m 33% bullet rosettes 0% hexagonal plates 27% hollow columns 40% aggregates ARM-IOP - avg. of 2 cases (cirrus uncinus) Max length < 100  m 0% bullet rosettes 70% hexagonal plates 10% hollow columns 20% aggregates Max length > 100  m 75% bullet rosettes 0% hexagonal plates 0% hollow columns 25% aggregates Nasiri, S. L., B. A. Baum, A. J. Heymsfield, P. Yang, M. Poellot, D. P. Kratz, and Y. Hu: Development of midlatitude cirrus models for MODIS using FIRE-I, FIRE-II, and ARM in-situ data. J. Appl. Meteor., 41, , 2002.

Version 1Version 2Version 3 Particle Size Distributions (PSD) 12 PSDs discretized to 5 size bins, very crude 3 Averaged PSDs discretized to 27 size bins, based on our evaluation of Heymsfield’s data Based on Gamma distribution fits to PSDs; >30 bins (more bins for large crystal sizes) Microphysical Data Source FIRE-I, FIRE-II, and older; difficult to trace back to source FIRE-I, FIRE-II, ARMFIRE, ARM, TRMM, SHEBA, CRYSTAL Habit Distributions and Habits Exactly the same for each model; based on plates, solid/hollow columns, 2D bullet rosettes, aggregrates Varies by model; based on plates, solid/hollow columns, 2D bullet rosettes, aggregrates Varies by model; New habits: Droxtals, 3D bullet rosettes Scattering models Scattering models computed in 1997; Based on Terra SRF Scattering models computed ; spectral resolution based on Terra SRFs Recompute scattering libraries with higher resolution in particle size and wavelength; add new parameters such as Qe; Dm Limitations Models based solely on midlatitude cirrus; not readily adaptable to global analyses Analysis of size spectra is complex; based solely on midlatitude cirrus TBD

Particle size distributions (PSD) in form of gamma distributions PSDs developed from polar, midlatitude, and tropical data Ice crystal scattering properties recomputed for a variety of habits (including new habits like the droxtal and 3D bullet rosette) Higher spectral resolution for scattering property calculations Higher resolution in discretization of large particle sizes What’s new for Version 3?

Particle Size Distributions Gamma size distribution* has the form: N(D) = N o D  e - D where D = max diameter N o = intercept  = dispersion  = slope The intercept, slope, and dispersion values are derived for each PSD by matching three moments (specifically, the 1st, 2nd, and 6th moments) Note: when  = 0, the PSD reduces to an exponential distribution *Heymsfield et al., Observations and parameterizations of particle size distributions in deep tropical cirrus and stratiform precipitating clouds: Results from in situ observations in TRMM field campaigns. J. Atmos. Sci., 59, , 2002.

Midlatitude Cirrus Clouds FIRE-1 (1986) FIRE-2 (1991) ARM IOP (2000)

Tropical ice cloud characteristics Form in an environment having much higher vertical velocities Size sorting is not as well pronounced Large crystals often present at cloud top Crystals may approach cm in size. Habits tend to be more complex Tropical Ice Clouds - TRMM

In-Situ Data: Gamma Distributions Individual particle size distributions: 2025 PSDs from TRMM and midlatitude (FIRE-1, FIRE-2, ARM) campaigns 331 PSDs from SHEBA (May) No way to tell location within cloud layer where PSD data were derived

In-Situ Data: Gamma Distributions

Effective Diameter vs. Median Mass Diameter D e calculated assuming only hollow columns Effect of habits is still being explored

Ice Crystal Habits Midlatitude Cirrus Tropical Ice Clouds Polar ice clouds - TBD

Simulated Particle Habits Replicator Particle Habits Note: the use of the droxtal for small particles is quite recent.

Small, Nonspherical Ice Crystals: Droxtals Yang, P., B. A. Baum, A. J. Heymsfield, Y.-X. Hu, H.-L. Huang, S.-C. Tsay, and S. Ackerman: Single scattering properties of droxtals. In press, J. Quant. Spectrosc. Radiant. Transfer, Geometry of ice crystals observed in an ice fog (after Ohtake, 1970)

Ice Crystal Profiles From Tropical Cirrus

Simulated Particle HabitsCPI Particle Habits

Suggestions for Future Models The exact meaning of our satellite-derived “effective diameter” continues to confuse many in the community because of the complexity of ice habits and the abundance of definitions What modelers seem to want is IWP One parameter that both in-situ aircraft and surface-based radar measurements provide is median mass diameter (D m ) Suggestion: Include D m and IWP as part of retrieval

Optical Depth - IWP 2 Parameter Solution Optical Depth - IWP 2 Parameter Solution *Heymsfield, Matrosov, and Baum: Ice water path-optical depth relationships for cirrus and deep stratiform ice cloud layers. Submitted to J. Appl. Met., Here’s one way to relate directly the visible optical depth and IWP* Includes midlatitude cirrus (FIRE-1, FIRE-2, ARM IOP) and TRMM data ( Heymsfield et al., J. Atmos. Sci., 59, , 2002 ) Issues: limited data from in-situ measurements can not assess how representative these data are

Optical Depth - IWP 3 Parameter Solution Optical Depth - IWP 3 Parameter Solution *Obtain IWP using layer-averaged median mass diameter D m and visible optical depth  v, where coefficients e 0, e 1 are determined for midlatitude and tropical clouds Advantages: readily obtain D m from radar data (e.g., ARM) can derive D m for each ice model determine  v from MAS, MODIS easier to validate the models this way, and provides a path to derive error estimates for IWP *Heymsfield, Matrosov, and Baum: Ice water path-optical depth relationships for cirrus and deep stratiform ice cloud layers. Submitted to J. Appl. Met., 2003.

If we include D m and IWP in the MOD06 product… Compare MODIS-derived IWP/Dm to ARM CART site retrievals of IWP/ D m Can also incorporate field experiment data (MAS vs. radar) Build error estimates from these comparisons as function of synoptic cloud type Validation Approach #2

Short term plans Developing set of microphysical models based on measurement- based set of PSDs from polar, midlatitude, and tropical data - Could use some guidance here Soon will be recomputing libraries of ice scattering properties to extend wavelength domain and range of particle sizes Will send set of models to Anthony Baran for independent testing using AATSR data Extending work to IR interferometer measurements as well as MISR and other imagers

Midlatitude Cirrus Midlatitude cirrus often show 3 distinct layers: - small particles in “generating region” near cloud top - growth region containing pristine ice crystals in middle region - sublimation layer near cloud base, with largest particles

Ice Crystal Profiles From the Cloud Particle Imager (CPI) from the ARM IFO in March, 2000 Ice Crystal Profiles From the Cloud Particle Imager (CPI) from the ARM IFO in March, 2000 For this profile in cirrus uncinus, note the prevalence of bullet rosettes. At each level within the cloud, there are also a number of very small crystals.

Imager Spectral Response Functions

Our set of 27 bins for discretization of the size distribution is too restrictive for convective clouds. Need to account for much larger particles near cloud top. The “aggregate” particle may be too compact an ice crystal, especially at very large sizes. Tropical Cirrus Issues