METR 415/715
Monday March 11 2013
Outgoing Longwave Radiation at top of atmosphere
• Broadband IR radiation• The PSD Map Room• The utility and limitations of OLR information– Daily averagesand anomalies– Weekly averages and anomalies– Monthly averages and anomalies– Seasonal (3-month) averages and anomalies
OLR Maps as indication of convective cloudiness
• Thick cumulonimbus cloud clusters reach top of tropical troposphere
• You can assume they act as black body radiators• There is relatively little absorption of OLR
coming out of these cloud tops to space• You can use Stefan-Boltzmann’s Law to get a
crude estimate of the cloud top temperatures and from that estimate their heights
Estimating Surface Temperatures using OLR
• Even in cloud –free environments, and even assuming that the emissivity of the ground is close to 1, you will greatly underestimate the ground temperatures using OLR data and S-B Law
• This is because the clear atmosphere has relatively low transmissivity in the IR part of the spectrum, primarily due to the absorption by water vapor
The use of anomaly maps
• Now that there are more than 30 years worth of continuous worldwide satellite coverage, we can construct climatologies of OLR for every day of the year
• Looking at any particular day’s average OLR vs. the average OLR for that particular day over the period of satellite record
• The day’s OLR – the average OLR for that day gives us the anomaly OLR for that day
Average OLR for March 9 2013
7-Day Average OLR
Monthly Average OLR
90-Day Average OLR Anomaly