using submillimeter to measure cloud ice mass from earth viewing satellites 11 october 2005 sirice...

Using Submillimeter to measure cloud ice mass from earth viewing Satellites

11 October 2005

SIRICE

Steve Ackerman/U.WiscDavid Starr/GSFC

K. Frank Evans/CSU

U.Wisconsin-GSFC-JPL

Why Submillimeter to measure cloud ice mass from earth viewing

Satellites?

Sat-Precip and Model Precip Validation Efforts


SIRICE Management Status Review September 27, 2005- Science

Slide 3


PIS. Ackerman (UW)

ALGORITHM APPLICATIONS VALIDATION

K.F. Evans (CU) D. O’C. Starr (GSFC) G. McFarquhar (UI)

T. L’Ecuyer (CSU) B. Soden (Miami)A. Heymsfield

(NCAR)

T. Greenwald (UW) A. del Genio (GISS) J. Mace (UU)

H. Revercomb (UW) A. Hou (GSFC) Z. Wang (WY)

P. Racette (GSFC) A. da Silva (GSFC) J. Wang (GSFC)

J. Spinhirne (GSFC) P. Norris (GSFC) S. Platnick (GSFC)

R. Lancaster (GSFC) B. Demoz (GSFC)

G. Skofronick-Jackson (GSFC)

R. Bennartz (UW)

Science Team

Science team is composed of internationally recognized leaders in ice cloud studies


Slide 4


Outline of Presentation

• Summary

• Why ice clouds?

• What is current knowledge of ice clouds?

• What are requirements:– Spectral region– Spatial and temporal sampling– What orbit

• Summary of objectives


Slide 5


Provide the global distribution of cloud ice at cloud-system-resolving scales

Ice water path: IWP - vertically-integrated (column) mass of ice particles per unit area, => the Earth’s Radiation Budget and linkage to the Hydrologic Cycle.

IWC weighted mean equivalent particle diameter (Dme). Crystal size => cloud

radiative properties and ice crystal fall speed (vertical ice mass flux), a key model parameter.

Need measurements of IWP and Dme

• Daily Global coverage (1600-km swath from LEO) at• Cloud-system resolving (10-km resolution requirement) with• Useful accuracy (±25% requirement: Ohring et al, 2004; GCSS, 2000) over• Dynamic range (5-5000 g m-2 and 40 – 800 microns)

required to quantify coupling of the Global Water and Energy Cycles (Precipitation and Radiation Budget)


Slide 6


Why ice clouds?

Ice clouds are:

• Crucial to Earth’s Radiation Budget (Energy Cycle)(~large area coverage, highly variable properties)


Slide 7


Why ice clouds ?

Ice clouds are:

• Crucial to Earth’s Radiation Budget (Energy Cycle)(~large area coverage, highly variable properties)

• Difficult to measure with traditional technology (ICSSP/GOES, MODIS, AIRS, AMSU-B, CloudSat/CALIPSO)- Estimates of global mean IWP range from 20 to 150 g m2 !!!


Slide 8


Why ice clouds?

Ice clouds are:

• Crucial to Earth’s Radiation Budget (Energy Cycle)(~ large area coverage, highly variable properties)


• Generated directly by Precipitating Cloud Systems (Water/Hydrologic and Energy Cycles), or sublimated ice and vapor detrained earlier

What doesn’t fall out as Precipitation, gets detrained !


Slide 9


Why are ice cloud measurements needed?

Ice is transported into the upper troposphere by:

Convection (thunderstorms) Large scale lifting (e.g. fronts)

This ice will:• Lead to heating associated with the ice – energy and hydrological cycle• Sublimate and moisten upper/mid troposphere - impacts energy budget• Fall out as precipitation – impacts hydrological cycle

=> cirrus=> cirrus


Slide 10


Why ice clouds ?

Ice clouds are:






Slide 11


Why ice clouds?

Ice clouds are:





• Estimates of global mean IWP range from 20-150 g m2 !!!

=> Ice clouds are a major unconstrained/free tuning knob (largest remaining uncertainty) available to GCM’s to achieve agreement with observations of global energy budget (ERBE, CERES) and precipitation (AMSR, TRMM, GPM).


Slide 12


What is our current knowledge?

The large discrepancy in mean IWP between climate models is one demonstration of our poor knowledge of ice mass in the atmosphere.

The climatology of zonal, annual mean IWP from state-of-the-art global models.

Ohring et al (2004) note that for climate monitoring purposes, IWP must be measured to an accuracy of 25% and that no satellite missions meet this requirement. (NIST-NOAA-NASA workshop on Satellite Instrument Calibration for Measuring Global Climate Change)


Slide 13


What is our current knowledge?

The sensitivity of GCM tropical radiative and precipitation fields to IWP.

Global cloud ice measurements are essential for understanding the coupling of the global hydrologic and energy cycles.

Change in IWP (g m-2)

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Precipitation

If you change the IWP, you change the amount of precipitation:

=> more ice, less rain

Reflected Solar

If you change the IWP, you change the radiative energy budget:

=> more ice, brighter planet,

Outgoing InfraredWarmer surface?


Slide 14


What ranges do we need to measure?

Approximately 80% of the clouds have IWP less than 100 g m-2; these clouds contain less than 10% of the total ice mass.

Small IWP end is important for Earth Radiation Budget.

Large IWP end is important for the Hydrologic cycle.

Need to accurately measure the large range in ice mass.

The fraction of pixels with IWP less than a given value (blue) and the fraction of the total mass in

pixels with IWP less than a given value (red)

Fraction of pixels < IWPFraction of mass < IWP


Slide 15


Science Requirement: Range

Provide global measurements of ice water path (IWP) and median mass particle diameter (Dme).

These measurements will have the temporal and spatial sampling required for accurate regional averages needed to improve the modeling of ice clouds in climate models.

Scientific Measurement RequirementIWP in the range of 5 to 5000 g m-2

Dme in the range of 40 to 800 microns

Science Objective


Slide 16


What wavelengths do we need?

• Below 1500 GHz radiation interacts with ice particles primarily by scattering.

• The change in the upwelling brightness temperature (Tb) compared to clear sky is a function of IWP and particle size.

• Submillimeter-wave radiation is emitted upwards by water vapor in the opaque lower troposphere.

The physics of the measurements is well known.


Slide 17



• Cirrus significantly reduces the brightness temperature in the submillimeter part of the spectrum.

• The brightness temperature depression generally increases with frequency.

• Brightness temperature saturates slowly for large IWP.

• Polarization is a function of crystal shape

Simulations demonstrate sensitivity of submm observations to ice cloud properties.


Slide 18



• A demonstration of the retrieval and its errors: IWP and median mass diameter (with error bars) are retrieved with a Bayesian algorithm (Evans et al., JGR, Feb 2002) (see top figure). Validation is accomplished through comparison with the vertically integrated radar reflectivity. (see bottom figure). The retrieval applied to CoSSIR measurements agrees very well with radar reflectivity

Channel selection based on detailed trade studies.


Slide 19



• Retrieval errors in IWP as a function of IWP for combination of Submm, IR and Stereo.

• This is a result of detailed sensitivity studies to determine the optimum set of wavelengths and noise requirements for meeting retrieval requirements.

• One frequency with two linear polarization to determine particle shape.

• Knowledge of cloud altitude improves retrievals for less than 25 g m-2, more than 50% of the observed ice cloud frequency.

Channel selection based on detailed trade studies.


Slide 20


What is new and unique?

Submm is more then an evolution of existing observations – provides new spectral measurements of clouds at Submm wavelengths that compliment planned solar, infrared and microwave observations

When integrated with other coincident satellite measurements, Submm will uniquely provide the first complete description of the hydrometeor

content and structure of cloud systems.

MicrowaveCIMS

Solar, InfraredVIIRS

SIRICE


Slide 21


Why Submm?

• Recent submillimeter technology (MLS, CoSSIR)

• Well-understood strong physics and mature algorithms

• Enables multiple science pathways to model improvements– Global/zonal constraints (accuracy)– Regional/seasonal constraints (sampling)– 2-year global integrated system analysis via data assimilation

– Cloud system composites, seasonal/regional, to constrain the detailed cloud system models that underpin GCM’s (GCSS)

• Submm observations hugely enhanced if formation fly with microwave


Slide 22


Unique Measurements of Hydrological Cycle

microwave - precipitation

microwave – Liquid Water Path

Infrared – thin cloudsSolar – top of clouds

Submm – Ice Water Path

Need measurements a component of the hydrological cycle that we know little about – the amount of ice in the atmosphere.


Slide 23


Science Requirement: Complete Range

Scientific Measurement Requirement

IWP in the range of 5 to 5000 g m-2

Dme in the range of 40 to 800 micron

Instrument Functional RequirementTwo instruments:

Infrared and submillimeter wavelengths

Rigorous and comprehensive trade studies show….


Slide 24


Science Pathway

It is not enough to observe the zonal mean variables. Need observations as a function of process.

Convective and synoptic systems transport ice into the upper troposphere. Need to resolve these processes to improve models.

Large scale lifting

Convection

Latitude

Cloud ice generation in mm/day by ECMWF, July


Slide 25


Science Pathway

Scientific Measurement RequirementDaily near-global coverageSample storm system spatial resolution – convective and synoptic

Robust regional/seasonal statistics and data assimilation for global description of complete cloud component of global hydrological cycle.

=> wide swath for global coverage

Process resolving analysis and cloud system modeling. => Resolution


Slide 26


Spatial Resolution Requirement

Scientific Measurement RequirementSpatial resolution: field-of-view

Optimum field of view is a trade between instrument noise, uniform scene, and the scale of the weather phenomena.

These trade studies led us to a submm fov of ~10-15 km.

Cirrus along front extending across midwest, along with a 10 km circle for scale.

10 km fov


Slide 27


Spatial Coverage Requirement

Characterize IWP and Dme distributions at a cloud-process-resolving scale as a

function of cloud systems and meteorological process, thus quantifying the contribution of upper tropospheric ice production by deep convection and synoptic lifting.

Application of measurements to cloud system modeling research will improve our understanding of ice cloud processes needed for improved climate predictions.

Requires

Science Objective

Robust regional/seasonal climatology => Daily near-global coverage

2-year integrated Earth System analysis via Data Assimilation => Daily near-global coverage

Resolve cloud system processes/structure for many cloud systems, convective and synoptic => ~ 10 km resolution, broad swath coverage


Slide 29


Spatial Coverage Requirement

Scientific Measurement RequirementDaily near-global coverageSample storm system spatial resolution – convective and synoptic

Instrument Functional RequirementApproximately 10 km resolution

- trade of instrument noise and scale of weather systems

Conical scanning with a wide swath

- trade of instrument noise, rotation, and spatial coverage

Polar orbit (mission requirement)

- At ~ 833 km orbit => Conical Scanning Imager, ~1600 km swath


Slide 30


Orbit Selection

Scientific Measurement RequirementDaily near-global coverageApproximately 10 km resolution

Mission Functional RequirementSun-synchronous, morning/evening orbit

=> captures convection over tropical waters (morning, ice lags precip max) and continents (evening), fly with planned satellite that have visible, infrared and microwave measurements to allow complete cloud system characterization.

TRMM observations help with selecting equatorial crossing


Slide 31


Summary: Science Objectives

Provide global measurements of ice water path (IWP) and weighted median mass particle diameter (Dme).

These measurements will have the temporal and spatial sampling required for accurate regional averages needed to improve the modeling of ice clouds in climate models.

Characterize IWP and Dme distributions at a cloud-process-resolving scale as

a function of cloud systems and meteorological process, thus quantifying the contribution of upper tropospheric ice production by deep convection and synoptic lifting.

Application of measurements to cloud system modeling research will improve our understanding of ice cloud processes needed for improved climate predictions.

using submillimeter to measure cloud ice mass from earth viewing satellites 11 october 2005 sirice...

Documents

jpl slide

cloud ice mass

sublimated ice

ice cloud studies

radiation budget slide

wang gsfc

demoz gsfc

platnick gsfc