METR 415/715 Monday March

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

7-Day Average OLR

Monthly Average OLR

90-Day Average OLR Anomaly