A New Global Data of Cloud Vertical Layers and A New Global Data of Cloud Vertical Layers and Implications for Model SimulationsImplications for Model Simulations

JCSDA Science Workshop, May 31-June 1, 2006, MD

Zhanqing LiZhanqing LiDepartment of Atmospheric and Oceanic Science & ESSICDepartment of Atmospheric and Oceanic Science & ESSIC

University of MarylandUniversity of MarylandFu-Lung ChangFu-Lung Chang

National Institute of Aerospace (NIA) National Institute of Aerospace (NIA)

Science Questions

Do we have a sound global cloud data in terms of cloud vertical structure and cloud optical properties?

To what extent do cirrus clouds overlap with lower-level clouds on a global scale?

How much artifact and uncertainty exist in in current satellite and model simulation cloud products?

Status of Model Simulation of Cloud-Layering

Satellite cloud properties

Model validation(Zhang et al. 2005,

JGR)

Status of Satellite Remote Sensing of Cloud-layering

Both MODIS and ISCCP cloud retrieval algorithms are applied to April 2001 Terra/MODIS L1B radiance data.

Determination Cloud Top Altitude from Satellite

ISCCP and conventional methods:

Use a single IR-window

channel (11 m)

MODIS:

Use multi-spectral

IR sounding channels

(11-14.3 m)

Principles of Our New Method 11-m IR

temperature

uppermost (CO2-slicing) cloud-top temperature

0.65-m cloud VIS optical depth

high cloud

low cloud

high cloud

low cloud

Algorithm (Chang and Li 2005, JAS)

Lookup-table radiances are generated based on an ice-over-water cloud radiative transfer calculations.

Classification of Cloud Categories

High1 - single-layer cirrus cloud (IR < 0.85);

High2 - overlapped cirrus cloud (IR < 0.85);

High3 - thick high cloud (IR 0.85);

Low1 - single-layer lower cloud;

Low2 - overlapped lower cloud;

*High2 and Low2 are retrieved simultaneously.

Validation over the ARM SGP Site Validation is based on

comparisons with the Active Remote Sensing Cloud Locations (ARSCL) data from DOE/ARM.

Overlapped cirrus clouds (open points) and low clouds (filled points) are validated during March-November 2001 by comparing the ARSCL and our cloud-top pressures (a) and cloud-top temperatures (b).

A Distinct Bimodal Distribution of High and Low Clouds

A Distinct Bimodal Distribution of High and Low Clouds

Apr.-Nov. 2001 at SGP Apr.-Nov. 1999 at NAU

Zonal-mean Cloud Properties

Cloud Top Pressure Cloud Top Temperature Cloud Optical Depth

Our Low Cloud Amount

January 2001 April 2001

July 2001 October 2001

Mid Cloud Amount (Including 440-680 mb)

January 2001 April 2001

July 2001 October 2001

Total High Cloud Amount (High1/High2/High3)

January 2001 April 2001

July 2001 October 2001

Overlapped Cloud Amount

January 2001 April 2001

July 2001 October 2001

Comparing High, Mid, and Low Cloud Amounts

Our MODIS retrievals with overlapping

MODIS data (Collection 4)

Retrievals from the Visible-IR method

H H H

M M M

L L L

H: < 440 mb, M: 440 mb-680 mb, L: > 680 mb

Comparing Ours, MODIS and ISCCP Cloud Layer Structures Probability of Cloud Occurrence Layer Cloud Amount

Ours

MODIS

ISCCP like

Comparing Zonal-mean High/Mid/Low Cloud Amounts

Comparing Cloud-Top/Cloud-Optical-Depth Joint Distributions

All MODIS, ISCCP, and our cloud retrieval algorithms are applied to April 2001 Terra/MODIS L1B radiance data.

Evaluating Cloud Fields Generated by the NCEP Models

Implement and validate our retrieval algorithm

Get cloud data from the model for selected days & months

Retrieve cloud properties from MODIS satellite

Comparing cloud layers derived from satellite and models

Quantify major discrepancies

Study the causes for the discrepancies

Conclusions To date, most satellite and modeling cloud algorithms

adopt a single-layer cloud assumption, which cannot deal with cloud overlap situation.

For cirrus overlapping low clouds, conventional IR method tends to detect them as single-layer mid-level clouds; while MODIS treats them as single-layer high-thick clouds.

Our results show relatively ~30% more low clouds than the MODIS operational product owing to cloud overlaps.

Our cloud layer structure shows a distinct bimodal high-and-low cloud distribution with minimum cloudiness near 500-600 hPa,

ISCCP does not show the distinct cloud layer structure. Yet, it has a lot less high and low clouds, but more mid-clouds.