(Very) Preliminary Quality Assessment of Stratospheric AMSU Channels (Channels 9 – 14) Carl Mears Remote Sensing Systems

AMSU and SSU Weighting Functions AMSU 9 AMSU 10 AMSU 11 AMSU 12 AMSU 13 SSU 15x SSU 25 SSU 26 SSU 27

Some Results from the Troposphere and Lower Stratosphere

Problems with AMSU Mid-Troposphere Funny behavior for near-limb views

Problems with AMSU (Near Tropopause) Other channels at least as bad! Some indication that target factor could be FOV dependent!

Problems with AMSU How do we figure out which AMSU instrument is bad (or at least, less bad) Radiosondes probably not accurate enough Time period too short for water vapor to help NOAA-16 farther way from NOAA-14 MSU (but this is an old instrument) Solution: Figure out which AMSU has a more consistent dataset by looking at all channels (and nadir vs limb views)

Probable vertical structure of trends Trend Height Tropopause

Trends – NOAA-15 and NOAA-16 Tropical Oceans, 30S to 30N NOAA-15: Fairly consistent except for Channel 6. NOAA-16: All channels inconsistent except for (maybe) channel 4.

Trends – NOAA-15 and NOAA-16 Tropical Oceans, 30S to 30N, NOAA-15: Fairly consistent except for Channel 6. NOAA-16: All channels inconsistent except for (maybe) channel 4. Conclusion: NOAA-16 more likely to be the problem – NOAA-16 is removed.

Now, the Stratosphere Basis strategy – apply the same analysis to the stratospheric channels to see if NOAA-16 has problems for these channels too. Very preliminary, since we have not performed any diurnal adjustment. Difficult to evaluate channels 11 and 14 due to short (or zero) overlap

Trends, , K/decade 60S to 60N Trends broadly consistent for all stratospheric channels Nadir-limb difference seems too large - related to diurnal drift?

Channel 10 Time Series Temperature Anomaly NOAA-16 – NOAA 15 For Channel 10, everything is fairly well behaved.

Channel 12 Time Series Temperature Anomaly NOAA-16 – NOAA 15 For Channel 12, descending node shows significant drift.

Adjusting for drifts in measurement time NOAA satellites drift in local measurement time If uncorrected, these would lead to spurious long-term signals in the dataset. NOAA-15 NOAA-16

NOAA-16 minus NOAA-15 differences by field of view. Drift in descending node strongly dependent on field of view. At least part of this is due to drift in measurement time.

Conclusions Where we can evaluate them, the stratospheric channels on AMSU appear to be in better shape than the tropospheric channels. Need to come up with a reasonable diurnal adjustment –4 AMSUs with different measurement times –Stratospheric model data with output every 3 hours –Microwave Limb Sounder probably not useful.