# Presentation: 196472

## HIRDLS Methane and Water Vapor Products: Status and Future Development

**T. Eden****1****, H. Worden****1****, J. C. Gille****1,2****, C. Cavanaugh****1****, C. Craig****1****, C. Hartsough****1****, D. Kinnison****1****, and R. Khosravi****1**
***1******NCAR,  Boulder, CO, USA and ******2******University of Colorado at Boulder, Boulder, CO, USA***

**Abstract**
- The current status of unreleased HIRDLS methane and water vapor products are presented, with an emphasis here that both products are “*works-in-progress*.” A top-level assessment of both retrieved products show decent orbital morphology for days close in time to the “correction day” (*i.e*., data from a spacecraft pitch maneuver used to characterize the atmospheric portion of the blockage emission), but the values are inconsistent when compared against correlative data or climate models.  Furthermore, the orbital morphology degrades when data further away in time from the correction day are analyzed, which appears to imply unaccounted-for sources of variability. Ultimately, the success of the HIRDLS methane and water vapor products hinges on the effective removal of the obstruction emission from the science scan profiles. Some discussion of current and future work will round out this poster presentation.

**1. Methane: Current Status For a Day in July 2006**

**Vertical distribution of CH****4 ****volume-mixing ratio (vmr) zonal means for July 13, 2006: **Left panel: HIRDLS v004 results, at a latitude bin width of 5; right panel: WACCM3 results for the same day (latitude bin width of 4). Compared to model data, HIRDLS results exhibit high values in the tropics (especially between 20-100 hPa. At high northern latitudes, HIRDLS is generally low below 6 hPa. **Note:** For the HIRDLS data, ~5500 scans are used to make the daily zonal means. **   **    ** **

**2. Current Status of HIRDLS v004 Water Vapor: Tape Recorder Comparison With MLS **

**3. Time Evolution of the HIRDLS Methane Product**** **

**4. Retrieval Sensitivity Study to Radiance Errors**
**For Methane and Water Vapor Channels**

**Zonal mean time evolution of v004 methane data: **Beginning on the “correction day” (**plot a**), and moving forward in time, it is interesting to observe the changing orbital morphology of the methane signal in the stratosphere, which is primarily related to the changing obstruction emission over time. Large values of methane appear in the tropics in July 2006 **(plot b**), and begins to diminish in magnitude in August (**plot c**). Moving into late October (**plot d**), lower values return, but the tropical upwelling is still larger than expected. In December (**plot e**), larger-than-expected values are now prevalent for northern mid to high latitudes, through the upper stratosphere. The same abnormal behavior in the northern hemisphere continues, albeit a bit differently, during late February 2007 (**plot f**). The main feature in the bottom-row figures (**plots g-i**) is the lobes of maximum methane are migrating towards higher latitudes. Although there is seasonal variability, the geophysical morphology is not completely cyclical with respect to season, which implies a more complicated variability scheme is present.

**a)**

**b)**

**c)**

**d)**

**e)**

**f)**

**g)**

**h)**

**i)**

**2005-2007 water vapor tape recorder above the tropical tropopause. **Top and middle panels show zonal mean (10°S to 10°N) vertical profiles of water vapor as a function of time (day) for a) MLS and b) HIRDLS. Panel (c) shows the difference, where MLS zonal mean profiles were interpolated to the HIRDLS pressure grid. The time variation of the difference demonstrates both seasonal and interannual biases. The HIRDLS data shown here used the radiance correction from May 18, 2006, or day 503 on the above plots. Note that panel (b) shows significant improvements over HIRDLS V3 data where water vapor values between 100 and 70 hPa would saturate the upper level of the color scale.

**Radiance error sensitivity: **Latitudinal averages for simulated changes in HIRDLS channel radiances (after Kapton correction)  for 10% error in either CH4 or H2O VMR. This allows us to assess where profiles are most affected by systematic errors and the Kapton correction accuracy that needs to be achieved.

**5. Conclusions and The Future**

- Prospects are high for obtaining usable HIRDLS methane and water vapor products. However, more work in specific areas needs to be performed. Results from the radiance error study suggest that our uncertainty in removing the obstruction emission is reasonably good at most altitudes of interest; however, other types of unaccounted variability remain.
- Methane and water vapor face similar issues, when it comes to producing good radiances for the retrieval algorithm, which is not surprising on several levels. Physically, detector channels 17 and 18 occupy two positions of the most spaceward row of the focal plane. Although they are two of the most “open” channels in the array, their signals occur at more earthward elevation angles, which has its own set of problems. For instance, measurable signal occurs in an elevation-angle region where the scan mirror makes contact with the obstruction material, causing material oscillation and a complicated modulation to the signal in this region. Suffice it to say, if the removal of the obstruction emission is not accurate in this region, the entire radiance profile below it is adversely affected. The majority of the current effort has been focused systematically on understanding this region of variability, both in a spatial and temporal sense.
- The current version of the HIRDLS data has produced notable improvements to previously released products. Both methane and water vapor have also improved, but the remaining inaccuracies preclude their use in quantitative studies. Our aim is to have the next release of HIRDLS data include these two products, along with preliminary validation.

**http://www.eos.ucar.edu/hirdls/**

**Aura Science Team Meeting, October 27-30, 2008, Columbia, MD**