# Presentation: 687232

## Dehydration, cirrus clouds, and wave activity in the tropical tropopause layer during the warm and cold tropopause temperature season

**Dehydration, cirrus clouds, and wave activity in the tropical tropopause layer during the warm and cold tropopause temperature season**

- Holger Vömel1), H. Selkirk2), J. Valdes3), J. Valverde-Canossa3), W. Stolz4), J. A. Diaz5), G. Peng6), F. Hasebe7), T. Shibata8), N. Komala9), S.Saraspryia9)
- 1) Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA 2) Bay Area Environmental Research Institute, Mountainview, CA, USA, 3) Universidad Nacional, Heredia, Costa Rica, 4) Instituto Meteorológico Nacional, 5) Centro Nacional de Alta Tecnología, 6) Aerospace Corporation, 7) Hokkaido University, 8) University of Nagoya, 9) LAPAN, Bandung, Indonesia

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- Ozone and water vapor observed on 14 January 2006 at Biak, Indonesia. In both species the cold point shows the lowest values of the campaign.

- Relative humidity and backscatter ratio measured by lidar. There is weak indication for thin cirrus at the cold point with relative humidity over ice at 190% and average backscatter ratios not larger than 2.

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**Abstract:**
- A considerable number of campaigns studying the tropical tropopause dehydration processes have taken place during the northern winter months, which corresponds to the season of cold tropopause temperatures. Few observations have taken place during the season of warm tropopause temperatures. Ticosonde-Aura campaigns took place at Alajuela and Heredia, Costa Rica in July 2005, January/February 2006 and July 2006, with frequent launches of CFH water vapor instruments and ECC ozone sondes in cooperation with the Laboratory for Atmospheric Chemistry (LAQAT) of the Universidad Nacional at Heredia. These sondes provide detailed observations of the water vapor and ozone in the tropical atmosphere from the surface to the middle stratosphere. The observations took place both during the warm and cold tropopause temperature season. During the northern summer season the tropopause region exhibits water vapor amounts generally higher compared to mean stratospheric values. However, the coldest tropopause events during July-August show drying to well below mean stratospheric mixing ratios.
- Radiosondes, which were launched 4 times daily, provide a high resolution picture of temperature and wind in the upper troposphere and lower stratosphere and show that the cold events are related to wave activity in the UTLS region. There is a strong correlation between the anomalies in temperature, zonal wind and ozone.
- Simultaneous observations of water vapor using the CFH and lidar backscatter ratio at Bandung, Indonesia in December 2004 and at Biak, Indonesia in January 2006 provide the first correlation data between CFH relative humidity and cirrus clouds in the tropical western Pacific region. These observations indicate that large values of supersaturation can be achieved, and that the largest values are typically reached in the absence of cirrus clouds. The comparison of observations at Biak and at Heredia, Costa Rica in January 2006 show, that the coldest air, the lowest amounts of water vapor and the largest values of supersaturation over ice is observed in the Western Pacific region, in agreement with the geographic distribution of the coldest tropopause regions. Wave activity is able of modifying the occurrence of high supersaturation and clouds at the tropopause.

- At Costa Rica we obtained 24 water vapor profiles during July 2005 (blue) and 15 water vapor profiles during July 2006 (red). The tropopause is relatively wet with values between 5 and 8 ppmv. In July 2005, two soundings show values much below the average, reaching around 3 ppmv. Although the lower stratosphere is slightly drier in 2006, distinct dehydration events were not observed. However, two events showing higher water vapor than average were observed.

- At Biak, Indonesia we obtained 9 profiles of water vapor and ozone. Due to the cold tropopause season and the location in the region of coldest tropopause temperatures, the tropopause region is very dry showing values between 1 and 2 ppmv. One event was observed, with the water vapor minimum at 18.5 km and relative humidity over ice at 190 %. A second event shows the water vapor minimum at 17 km with a minimum value of 0.8 ppnv.

**Observations**

- Contact: Holger.Voemel@Colorado.edu

- Dehydration event 19 July 2005. The upper troposphere is saturated up to the cold point. The lowest observed mixing ratio is 2.4 ppmv.

- Ozone mixing ratio for this event. Ozone is lowest at the water vapor minimum and the highest of the entire data set at the water vapor maximum above the cold point.

**Dehydration event at Costa Rica 19 July 2005**

- The temperature anomaly shows a cold anomaly propagating downward over 4-5 days prior to the observation of the dehydration event. The anomalies in zonal and meridional wind indicate a combination of Kelvin wave and Rosby Gravity wave mode.

- 25 July 2005

- 11 July 2005

**Wave event 25 July 2006**

- The temperature and wind anomalies show less wave activity in July 2006 compared to July 2005. The warm anomaly at 16 km on and before July 25 corresponds with high ozone and water vapor observations.

- The water vapor profile on 25 July 2006 shows the highest amount of water vapor at 16 km, which is the cold point tropopause.

- Ozone also exhibits a maximum at 16 km, although not the highest value of the campaign.

**Dehydration event at Biak 14 January 2006**

**Dehydration event at Biak 12 January 2006**

- On 12 January 2006 the sounding detected a double tropopause with the cold point tropopause at 17.5 km and the lowest water vapor mixing ratio at 18.5 km. At this layer ozone shows stratospheric values indicative of secondary dehydration.

- The temperature, ozone and wind anomaly shows a downward propagating anomaly detectable over the previous 5 days. The wind relationships are indicative of a Kelvin wave. Similar to the dehydration event at Costa Rica in July 2005, extreme dehydration was observed at the time when the cold anomaly has reached and modified the local tropopause.

**Tropical waves at Biak January 2006**

- Costa Rica

- Biak, Indoensia
- January 2006