# Presentation: 490082

## Retrieval of Cloud Phase and Ice Crystal Habit From Satellite Data

- Sally McFarlane, Roger Marchand*, and Thomas Ackerman
- Pacific Northwest National Laboratory

## Introduction

- Knowledge of cloud phase and crystal habit is fundamentally important to remote sensing and climate simulations
- The shape of a particle affects the scattering of light such that water droplets and ice crystals of various habits have different phase functions
- Multi-angle Imaging Spectro-Radiometer (MISR) measures radiances at 9 different angles – We can use this angular information to discern particle phase and habit, but must also consider the particle size.
- Particle size can be simultaneously determined using near-infrared radiance from the Moderate resolution Imaging Spectroradiometer (MODIS).

## Retrieval

- Calculate radiance using state of the art radiative transfer model; ice scattering properties from Yang et al. (2000) database
- Retrieve best fit re, IWP, and crystal habit by minimizing deviation between modeled and measured reflectance over all cameras
- Currently assuming single layer cloud with one particle habit

## Case Study 1: Cirrus at ARM SGP site

*MISR nadir view image*

*ARM millimeter wave radar reflectivity*

## Case Study 1: MISR Only Retrieval Results

- Plot shows retrieval metric, , as a function of best-fit effective radius for a range of IWP values for the March 6, 2001 cirrus case when only the MISR reflectances are used in the retrieval.
- Water is clearly the worst fit to the observed reflectances.
- Hollow columns are the best fit for Re< 60 um; above 60 um several crystal habits appear equally valid.
- Little sensitivity to particle size using only the MISR visible wavelength.

## Case Study 1: MISR and MODIS Retrieval Results

- Top panel shows retrieval metric, , as a function of best-fit effective radius for a range of IWP values for the March 6, 2001 cirrus case using  MISR and MODIS reflectances in the retrieval.
- Each particle type now shows a clear minimum in the metric as a function of particle size.
- Water is the worst fit; hollow columns are the best fit.
- Bottom panel shows retrieved optical depth as a function of best-fit effective radius for a range of optical depth.
- Wide range of optical depth with crystal type; relatively little variation in optical depth with crystal size.

## Case Study 1: Effect of crystal habit on retrieved optical depth

| Habit | Metric() | Reff | IWP |  |
| --- | --- | --- | --- | --- |
| Hollow Columns | .033 | 43.2 m | 88.3 g/m2 | 3.6 |
| 4-Bullet Rosettes | .038 | 45.1 m | 95.3 g/m2 | 3.7 |
| Rough Aggregates | .041 | 62.7 m | 103.0 g/m2 | 2.9 |
| Plates | .047 | 32.5 m | 107.6 g/m2 | 5.7 |
| Water | .143 | 100 m | 360 g/m2 | 5.7 |
| MODIS |  | 29.7 m | 77.0 g/m2 | 3.5 |
| Radar
Retrieval |  | 53.9 m
(48 – 58) |  110.3 g/m2 
(82.6-149.5) |     3.4
(2.4-5.1) |

## Case Study 1: Radar Z-V Algorithms

- New radar retrieval algorithms, which use reflectivity (Z) and Doppler velocity (V), can retrieve vertical profiles of particle size and IWC
- Retrievals are sensitive to crystal habit due to dependence of particle fall speed and effective density on habit
- Constraining the particle habit reduces the uncertainty in the radar retrievals

## Case Study 1: Z-V Results

*Profiles of effective radius retrieved from radar Z-V algorithm, assuming different crystal habits*

*Optical depth retrieved from radar Z-V algorithm, assuming different crystal habits.*

## Case Study 2: Altocumulus at SGP

## Case Study 2: Results

- Water is best fit; MODIS retrievals indicate mixed phase cloud; ARM microwave radiometer shows LWP of 40-80 g/m2
- Altocumulus actively growing as it moved over the ARM site; likely to have water at top of cloud
- Need sensitivity studies to determine depth in cloud to which retrieval is sensitive

*Retrieval metric as a function of best-fit effective radius for a range of IWP values for the June 10 altocumulus case at SGP. Both MISR and MODIS reflectances are used in the retrieval for this case.*

## Case Study 3: Cirrus cloud over FARS(Facility for Atmospheric Remote Sensing, U. of Utah)

*Image from FARS lidar*

*Images from cloud particle imager (CPI )on in situ aircraft above FARS; crystals are primarily bullet rosettes and aggregates*

## Case Study 3: Retrieval Results

- In situ measurements were made within the same cloud system; roughly 180 miles away
- In situ measurements show bullet rosettes and aggregates; retrieval shows aggregates as best fit
- Need to study effects of habit mixtures in retrieval

*Retrieval results for FARS case using MISR and MODIS observations.*

## Conclusions

- Initial results show ability to discriminate cloud phase and crystal habit
- Need case studies with coincident in situ measurements of crystal habit for validation.
- Need to perform sensitivity studies to understand effects of habit mixtures; sensitivity to vertical structure; depth to which retrievals are valid
- Knowledge of crystal habit can constrain radar Z-V retrieval algorithms