the Air Vent

Because the world needs another opinion

Guest Post at Pielke Sr. on RSS UAH Differences

Posted by Jeff Id on November 4, 2009

Professor Ben Herman has done a guest post at Roger Pielke Sr’s blog on the differences we’ve seen in UAH and RSS.  The land sea effect was noted in blogland by Chad at treesfortheforest (link on right) but the experts in this case have been paying very close attention to this substantial issue.  Today I will add to this post a video showing the differences between UAH and RSS by month for 3 atmospheric levels.  The video is still uploading.   In the meantime check out Dr. Herman’s post below.

Update: Video added.

—————

Guest Post By Ben Herman Of The University of Arizona

Guest Weblog By Professor Ben Herman of the University of Arizona

In a recent post at the website The Air Vent titled

Land/Sea Bias In Satellite Temperature Metrics

the problem of correcting MSU (Micro Wave Sounding Unit) brightness temperature data for differences in the diurnal temperature variations between land and ocean was brought up. This is indeed an issue of considerable importance if the resulting data is to be used for determining temperature trends over time for climate change purposes. The reason is quite obvious. In a stable, non-changing thermal regime, due to orbital drift, the satellite will pass over any given latitude at different times of the day, thus causing a trend in the resulting temperatures, positive for crossovers starting at, say 7:00A:M to about 3:00P:M, and negative thereafter till the following morning.  Thus, to obtain the true trend (zero trend in the previous illustration) it is important to correct for these diurnal variations.

Read the rest at Roger Pielke’s blog HERE.

===========================

Abstract from Ben Herman’s paper:

Using limited time period trends as a means to determine attribution of discrepancies in microwave sounding unit–derived tropospheric temperature time series

Robb M. Randall

Department of Atmospheric Sciences, University of Arizona, Tucson, Arizona, USA

Institute of Atmospheric Physics, University of Arizona, Tucson, Arizona, USA

Benjamin M. Herman

Department of Atmospheric Sciences, University of Arizona, Tucson, Arizona, USA

Institute of Atmospheric Physics, University of Arizona, Tucson, Arizona, USA

Limited time period running trends are created from various microwave sounding unit (MSU) difference time series between the University of Alabama in Huntsville and Remote Sensing System (RSS) group’s lower troposphere (LT) and mid troposphere to lower stratosphere channels. This is accomplished in an effort to determine the causes of the greatest discrepancies between the two data sets. Results indicate the greatest discrepancies were over time periods where NOAA 11 through NOAA 15 adjustments were applied to the raw LT data over land. Discrepancies in the LT channel are shown to be dominated by differences in diurnal correction methods due to orbital drift; however, discrepancies from target parameter differences are also present. Comparison of MSU data with the reduced Radiosonde Atmospheric Temperature Products for Assessing Climate radiosonde data set indicates that RSS’s method (use of climate model) of determining diurnal effects is likely overestimating the correction in the LT channel. Diurnal correction signatures still exist in the RSS LT time series and are likely affecting the long-term trend with a warm bias. Our findings enhance the importance of understanding temporal changes in the atmospheric temperature trend profile and their implications on current climate studies.

============================

The video is of the differences between RSS and UAH over the complete record.  It gets interesting where in 2002 UAH switched from the NOAA satellites which don’t keep stable orbits to AQUA which has station keeping thrusters.  It’s important to note that in the past RSS and UAH had an opposite decay satellite to help compensate for inacuracies in diurnal correction.  Currently RSS only has NOAA15 but this is indicative of only half of the signal in the past.  Post 2002 the single satellite is the whole signal and the inacuracies in RSS dirunal corrections are highly visible.  Watch the lower  stratosphere oscillate wildly in recent years, you can then replay it and see some of the variance in the lower troposphere as well.  Finally, Chad at treesfortheforest noted that the difference in trend between the two was land/ocean based and in the still image below you can see Australia and South America are blue while being surrounded by oceans of red.

 

RSS-UAH temperature 3levels377

Click to play

 


4 Responses to “Guest Post at Pielke Sr. on RSS UAH Differences”

  1. Jeff Id said

    Thanks to TTCA for the link.

  2. timetochooseagain said

    Much obliged.🙂

  3. Carrick said

    Very nice article by Randall and Herman. It shows the value of open communication among parties.

    Who would have dreamed that such highly technical details would get such wide-spread air play even 10 years ago?

  4. John M said

    …indicates that RSS’s method (use of climate model) of determining diurnal effects is likely overestimating the correction in the LT channel.

    Had never heard that before.

    Seems a strange way to do it, especially since some folks like to point to this dataset to support the models.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

 
%d bloggers like this: