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 Studies Department 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

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

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

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. 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

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

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