# Presentation: 639915

## Recent Stratospheric Water Vapor Measurements Over Boulder, Colorado:

**Comparison of Balloon and Satellite Observations **
- _Samuel Oltmans__1_, Dale Hurst2,1, Karen Rosenlof3, Gabriele Stiller4, Emrys Hall2,1, and Eric Ray2,3
- 1 NOAA Earth System Research Laboratory, Global Monitoring Division, 325 Broadway, Boulder, Colorado, 80305, USA
- 2 CIRES, University of Colorado, Boulder, Colorado 80309, USA
- 3 NOAA Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, Colorado, 80305, USA
- 4 Institute for Meteorology and Climate Research, Forschungzentrum Karlsruhe, P.O. Box 3640, Karlsruhe D-76021, Germany

**Introduction**
**Longer term measurements of water vapor in the stratosphere are very limited. The only continuing measurement of water vapor in the stratosphere with a multi-decadal record is the balloon profile measurements from Boulder, Colorado that  began in 1980. With the termination of the HALOE measurements on UARS, a long-term, high quality satellite record came to an end. More recent measurements such as MLS on Aura, ACE-FTS and MIPAS are producing quality stratospheric observations. The balloon measurements over Boulder span both the HALOE and more recent satellite observations. Here a comparison is presented between the balloon water profiles at Boulder at the end of the HALOE era with the recent observations from MLS, MIPAS, and ACE. **

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***Figure 3: Comparison of Boulder balloon profiles with profiles from ACE-FTS (1 day time difference for July profile: 28 ACE profiles compared with 12 balloon profiles)) and Envisat/MIPAS (11 comparisons). ***

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**Recent Improvements in the Balloon Hygrometer and **
**Corrections to Older Soundings **
**The balloon soundings are made with a cryogenically cooled frost point hygrometer.  In recent years several improvements have been made in the hygrometer that have dramatically reduced its size and weight and increased its ease of use. Throughout the measurement record, however, the instruments have been calibrated using the same NIST traceable temperature scale. Two versions of the hygrometer are currently in use (NOAA/GMD and CFH). These have several differing features and somewhat different calibration procedures, however, they use the same calibration scale and produce highly comparable results in the upper troposphere and stratosphere (Fig. 1).**

***Figure 2: Comparison of water vapor profiles over Boulder from Aura-MLS and the balloon-borne frost point hygrometer. Left: Example of an individual sounding from March 3, 2006. Right: Average difference and standard deviation  between MLS and balloon measurements (red) and the average mixing ratio from the frost point soundings (black). Approximately 70 profiles are included in the comparison.***

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***Figure 4: Time series of water vapor profiles over Boulder. Left: 16-24 km layer averages from balloon profile measurements over Boulder (black diamonds) with a model fit and a smooth curve representing the change. Middle: Growth rate of water vapor computed by differentiating the smooth curve in the leftmost panel. Right: 17-22 km layer averages of water vapor mixing ratio over Boulder obtained by MIPAS (from Stiller et al., 2008).***

**Conclusions**
** ****Recently developed versions of the balloon frost point instrument give consistent results with earlier measurements.**
** ****Both the microwave and infrared limb scanning profiles show good agreement with the Boulder balloon frost point water vapor measurements.**
**The long term series from Boulder shows an overall increase in water vapor mixing ratio (0.5 ****± 0.1 %/year), The 2001 decline has significantly contributed to the moderation of the trend.**
** ****Recent measurements hint at a possible recovery from the lower amounts that appeared beginning in 2001. This is seen in satellite data sets as well.**

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***Figure 1: Comparison of results from two different versions of cryogenically cooled frost point hygrometers. Left: High resolution obs. ~1 Hz. Middle: 250 km averages.***

**Comparison Between Balloon and Satellite Profiles**
**The largest number of satellite comparison profiles with the Boulder balloon measurements are from MLS (Fig. 2). There are approximately 70 unique comparisons (one MLS profile matched with one balloon profile) included over the period September 2004 – August 2008. There is essentially no bias in the 120-15 hPa (~15-28 km) altitude range.**

**Longer Term Changes in Water Vapor Over Boulder**
**The stratospheric water vapor time series over Boulder than began in 1980 (Fig. 4) showed increasing mixing ratios up to 2000 (Oltmans et al., 2000) with a drop, especially in the lower stratosphere, in 2001 (Randel et al., 2006; Scherer et al., 2008). The shorter HALOE record (1992-2005) shows the decline in 2001 but there is some ****discrepancy between the changes seen by HALOE and those seen in the balloon measurements (Fig. 5b&c) during the overlapping measurement period (Randel et al., 2006; Scherer et al., 2008).**** **

***References:***
***Stiller, G. et al (2008) Global stratospheric water vapor distributions from MIPAS/Envisat for the period 2002-2008, 4******th****** SPARC General Assembly. Bologna, Italy. September 2008.***
***Urban, J. et al (2008) Spatio-temporal variability of stratospheric water vapour as observed by Odin, 4******th****** SPARC General Assembly. Bologna, Italy. September 2008.***
***Scherer, M.  et al. (2008), Trends and variability of midlatitude stratospheric water vapour deduced from the re-evaluated Boulder balloon series and HALOE, Atmos. Chem. Phys., submitted.***
***Randel, W.J. et al. (2006), Decreases in stratospheric water vapor after 2001: Links to changes in the tropical tropopause and the Brewer-Dobson circulation, J. Geophys. Res., 111, D12312.***
***Oltmans, S.J.  et al. (2000), The increase in stratospheric water vapor from balloonborne frostpoint hygrometer measurements at Washington, D.C. and Boulder, CO, Geophys. Res. Lett., 27, 3453-3456.***

**As discussed in Scherer et al. (2008) corrections were made to earlier data and two quality checks were applied more consistently to the re-evaluated NOAA FP observations beginning in 1991 when data were available at higher time resolution with the conversion to a digital instrument. **

**There are not as many coincident measurements between the balloon profiles at Boulder and ACE-FTS (Fig. 3). With MLS the coincidences between the satellite overpass and the balloon sounding are all within the same day. The coincidence criteria with ACE has been relaxed to several days because of the many fewer overpasses. However, the agreement between the ACE and balloon profiles is very good. Coincident MIPAS overpasses are also limited (11) but there is also good agreement with Boulder balloon profiles. **

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**Both the balloon and recent satellite observations (Fig4; Stiller et al., 2008; Urban et al., 2008 - measurements from Odin/SMR) suggest a possible slow recovery from the dramatic drop in water vapor values that took place in the lower tropical stratosphere beginning in 2001 that was seen over Boulder as well.**

***Figure 5: Trend in water vapor over Boulder. Left: 1980-2008 trend in four layers in %/year from balloon profile measurements. Middle: Trend from the balloon measurements during the HALOE period (1992-2005). Right: Trend from HALOE observations over Boulder. Panels (b) and (c) from Scherer et al. (2008) ***