# Presentation: 321588

## Tropopause Folds: Results from NOAA Unmanned Aircraft Systems (UAS) Demo and Network Observations

_*J.W. Elkins*_*1**, D. F. Hurst**1,2**, F.L. Moore**1,2**, S. J. Oltmans**1**, *
*G.S. Dutton**1,2**, J. D. Nance**1,2**, B. A. Vasel**1,2**, B. Johnson**1**,*
*P.M. Lang**1**, and S. A. Montzka**1*
*1**NOAA/ESRL/GMD  and **2**CIRES*

## What is a tropopause fold?

- Folds are stratospheric intrusion of air that sinks beneath the upper tropospheric jet stream.
- Folds formed by a steepening of the tropopause at a jet core. Occurrences are common with major fronts and movement of polar stratospheric air into the midlatitudes.
- Folds are the dominant and most efficient form of short-term (days-weeks) Stratosphere-Troposphere Exchange (STE)
- Brewer-Dobson Circulation makes up the long-term (years), large scale STE of air from the upper tropical troposphere to polar stratosphere.

- Brewer-Dobson Circulation

- Fold

## Why are tropopause folds important?

- Transport (STE) is important because most sources gases are destroyed in the stratosphere, however ozone is produced there.
- Folds may play a role in the seasonal distribution of long lived source gases, N2O and CFCs by mixing lower stratospheric mixing ratios with tropospheric levels (Nevison et al., 2004; Liao et al., 2004).
- Folds may be key to removal of stratospheric sulfate aerosols by deposition into the troposphere.
- Clean, dry stratospheric air, rich in ozone and potential vorticity (PV) is transported downward to the troposphere.
- Tropospheric air (large amount of water, CO, aerosols, and low PV) also is advected upwards as well.

- A well-pronounced tropopause fold is forecast to occupy the
- mid- and upper troposphere above Friday's (Feb 5, ‘99) flight track.
- The following forecast is for 1800 UTC, Feb. 5.  Figure shows the
- forecast 2 PV (tropopause)isosurface for 1800 UTC Friday, Feb. 5.
- Potential temperature on this surface is indicated with shading.
- The tip of the fold penetrates beneath the 5 km level. Orange
- streamlines are shown at 3 km (10,000 ft) above sea level,
- for reference. (Univ. of Virginia, INTEX NA (Atlantic)Web page)

## NOAA/ESRL UAS Chromatograph for Atmospheric Trace Species (UCATS)

- Box weighs 22 kg (48 lbs.), 24.6 x 40.6 x 45.7 cm (9.7x16x18.1”), 45.6 liters
- Measures O3 once every 10 seconds (commercial unit 2B,Inc.)
- Measures N2O, SF6, CFC-11, CFC-12, halon-1211 once
-       every 70 seconds.  On board calibration.
- In the future, could measure( PAN, PPN) or (CO, H2, CH4)
-       for tropospheric mission.
-            Compounds in red are measured by Aura Satellite Instruments.

## Maps of 19 April 2005 Event

- PV plot courtesy of
- Leslie Lait, (NASA/GSFC)

## Observation of Tropopause Fold on the UAS Altair

- A

- B

- Five hour test flight finds fold above
- Gray Butte, CA airfield.

- PV plot courtesy of
- Leslie Lait, (NASA/GSFC)

- A

- B

## What is the cause of multiple peaks in ozonesondes at Trinidad, Head, CA (THD)?

- THD

- A tropopause fold.

- From Michael Ives internal
- Meeting talk on Monday.

- What is the cause of multiple peaks in ozonesondes at Trinidad, Head, CA (THD)?

- PV cross sectional plot courtesy of Eric Ray, ESRL/CSD
- Purple=polar air

## What is the frequency of folds at Trinidad Head?

- Established 3 necessary criteria for determining the presence of a fold.
- (1) Tropopause height lowered from 15 km.
- (2) Ozone (O3) slope changes of 50 ppb (100m level).
- (3) Small peaks of O3 observed in troposphere (<10 km)
- Used all sondes from 21 Aug 1997 to 3 Mar 2006.

- Typical sonde-no fold.

- Possible tropopause fold event

## Results from Trinidad Head (THD)

- 481 flights with 13 failed launches, 10 flights with no data to tropopause (not used).
- 47 out of 458 flights identified with possible folds (10.3%).
- Late winter and spring have the highest monthly frequency (right).
- Compares with previous ozonesonde study (Van Haver et al., 1996, GRL) of 2-5% of the total sondes have folds. A climatological study (Elbern et al., 1998) calculates an average of 11,000 fold days per year .

## Conclusions and further work.

- Folds last for days. Altair UAS is good platform for studying folds because of long endurance (20+ hours) and low speed (120 kts).
- Ozonesonde records with PV analysis confirm the presence of folds.
- Frequency of folds probably varies geographically, need to look at other ozonesonde records.
- Need to develop techniques to calculate the net flux into the troposphere.
- Addition of a water instrument (TDL, top right) to UCATS instrument will help since folds bring down low RH air.
- More Altair UAS missions this summer (NASA Fire) and next year (NASA Aura).  Addition of the UAS Global Hawk (bottom right) to atmospheric research is a plus with more payload.

- Randy May’s H2O TDL

- Global Hawk UAS