High Altitude Equatorial Clouds as Seen with the OSIRIS InfraRed Imager

A.E. Bourassa, D.A. Degenstein, N.D. Lloyd and E.J. Llewellyn

Institute of Space and Atmospheric StudiesDepartment of Physics and Engineering Physics

University of Saskatchewan

Outline

1) The instrument, the geometry and the technique

2) Some detections

3) Some statistics

4) To be done

Channel 1: 40 nm passband at 1530 nm

Channel 2: 10 nm passband at 1273 nm

Channel 3: 10 nm passband at 1263 nm

Each channel has 128 pixels, approximately 20 covered with mask

The IRI Instrument

LinearPhotodetectorArray

Optic AxisPixel

f

Field of View

LinearPhotodetectorArray

Optic AxisPixel

f

Field of View

SOLID EARTH

The Geometry To Scale

one image is collected every 2 seconds for approximately 2800 images per orbit

the orbit is approximately circular at 600 km above the equator

dusk-dawn orbit

in general only one hemisphere is lit

different illumination conditions for ascending and descending nodes

18 km cross section18 km cross section

Missing data from scan mode

Typical Data Collection

the scan or spacecraft nod results in missing IRI data

note the bright enhancements at the lower tangent altitudes

data for March, 2002

18 km cross section18 km cross section

Missing data from scan mode

Cloud detectionCloud detection

clouds clearly stand out against daytime nighttime trends

An Orbit of Limb Profiles

The Typical Profile

when the sun is up

this profile is measured most of the time at mid to high latitudes

it is even measured frequently at low latitudes

this profile is frequently measured near

the equator

The Typical and the not so Typical Profiles

layer at 18 km

when the sun is up

this profile is measured most of the time at mid to high latitudes

it is even measured frequently at low latitudes

note that the equatorial region is only fully illuminated on the ascending track of the satellite.

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-90 -45 0 45 90Latitude

SZ

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Ascending

Descending

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95

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-90 -45 0 45 90Latitude

SZ

A

Ascending

Descending

this allows for the characterization of an unperturbed signal

note that even for the lower sun on the descending node the equatorial enhancement is still there

Solar Conditions for March, 2002

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78 82 87 91 95Solar Zenith Angle

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ghtn

ess

(AU

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Unperturbed Conditions for March, 2002

the ascending and descending nodes are plotted as a function of Solar Zenith Angle

the criteria used for cloud detection

any scatter above a threshold level is considered a cloud

this is done with the vertical profiles and is evaluated as a function of altitude

Detected Clouds for March, 2002

detections for a single day in March, 2002

 contoured map of cloud detection for a three week period in spring, 2002

the clouds are between 17 and 20 km

all latitudes are sampled with approximately the same frequency.

Total Counts for April, 2002

Detected Clouds for January, 2002

Detected Clouds for February, 2002

Detected Clouds for March, 2002

Detected Clouds for April, 2002

Detected Clouds for May, 2002

More Detected Clouds

More Detected Clouds

More Detected Clouds

More Detected Clouds

More Detected Clouds

More Detected Clouds

More Detected Clouds

More Detected Clouds

A Different Look At the Data

The previous pictures just counted occurrences

The next set will look at percentages of occurrences

These pictures need more work as single hit outliers can really make a mess with the contouring routines that are used

Percentage of Hits in Early 2002

Percentage of Hits in Early February

Percentage of Hits in Late April Early May

To Be Done

1) Determine the best statistic to use

2) Process all data and map geographic, seasonal and time of day

3) Do more correlations with visual channels

4) Attempt to retrieve optical depths