# Presentation: 051915

## Discoveries From the First Year of MLS OH Measurements

- Herbert M. Pickett
- Jet Propulsion Lab, California Institute of Technology

## Previous Attraction

- Poster: Measured and Modeled HOx: Aura MLS, BOH, FIRS-2, and Ground-based Comparisons

- MLS average in upper panel is for latitude = [31.5, 36.5], longitude = [ -122, -72], and LST = 13.5 hr
- BOH and FIRS-2 profiles are for closest LST and assume a profile shape above 40 km
- Spectral profile is Doppler above 48 km
- Measurements are still sensitive to the column above 40 km
- MLS average in lower panel is a zonal mean for latitude = [24, 44] and LST = 13.5 hr

## Zonal Means for OH on June 22, 2005

- Dark

## Zonal Means for O3 on June 22, 2005

- H + O3  OH* + O2
- OH + O  H + O2
- ------------------------------
- O3 + O  2 O2

- Zonal Means for O3 on June 22, 2005

## Model Simulation of Night OH LIDAR Observations

## Modeled Meinel Emission of OH in Near-Infrared

## Slide 7

## Width = 2.5 km

- Width = 5.0 km
- Width = 7.5 km
- Width = 10 km

## Slide 9

## Modeled Radical Concentrations

- H + O2 + M  HO2 + M

- H + O3  OH* + O2

## Night OH Layer

- Layer at 82 km is associated with H + O3  OH(v) + O2 reaction
- Ozone catalysis with H and OH leads to ozone minimum
- Caltech 1-D model has been modified to include spontaneous emission in Meinel bands and collisional quenching (using S. Adler-Golden rates)
- Calculated chemical lifetime of HOx is ~1day at 82 km but ~1 month at 87 km
- Calculated width of level for OH(v=0) is 1.9 km at 81.5 km
- LIDAR signal has similar width and altitude
- Calculated emission height for Meinel bands is consistent with WINDII measurements of 87 km (width is ~10 km)
- MLS measurements show that the width, position, and area of the OH(v=0) layer is variable
- MLS measurements show that the layer persists in the dark pole near equinox and requires meridianal transport of H and O from solar-illuminated latitudes
- Chemical lifetimes require the transport to take place above 87 km

## A major Solar Proton Event occurred on 01/17/2005
MLS detected an increase in mesospheric OH and a decrease of mesospheric O3 in the Arctic polar night
Arctic results for OH and O3 are shown to the left 
Proton flux and OH response for the Arctic and Antarctic are shown above
MLS also detected an increase in mesospheric OH in the Antarctic polar day
No corresponding decrease in Antarctic O3 was found because the background O3 in the daylight Antarctic mesosphere is already very small
Thanks to C. Jackman for suggesting the OH-Sun connection

- Scaled Proton Flux

- Arctic OH

- Antarctic OH

- Arctic OH

- Arctic O3

- A major Solar Proton Event occurred on 01/17/2005
- MLS detected an increase in mesospheric OH and a decrease of mesospheric O3 in the Arctic polar night
- Arctic results for OH and O3 are shown to the left
- Proton flux and OH response for the Arctic and Antarctic are shown above
- MLS also detected an increase in mesospheric OH in the Antarctic polar day
- No corresponding decrease in Antarctic O3 was found because the background O3 in the daylight Antarctic mesosphere is already very small
- Thanks to C. Jackman for suggesting the OH-Sun connection

## Slide 13

## Slide 14

## Conclusions

- Key results for MLS HOx in the first year:
- Have validated OH with both BOH and FIRS-2
- Have validated HO2 with FIRS-2
- Have measured night OH near 82 km that is related for Meinel band emission in the near infrared and is responsible for a minimum in night O3
- Have seen OH produced from solar proton flares for the first time in 4 events
- MLS OH and HO2 profile measurements are being made every 25 seconds, with 240 samples per orbit and 14.5 orbits per day virtually continuously.
- Data set will allow comparison of HOx with models with season from 83S to 83N latitude
- Night observations of HOx are possible and represent half of the data set
- Other molecules measured by MLS (such as O3, H2O, HNO3,..) share a common footprint

## Acknowledgements

- Thanks to the many MLS and Aura team members who made many essential contributions to the mission success
- The BOH team members: Tim Crawford, Brian Drouin, and Pin Chen
- The OH validation collaboration: Ross Salawitch, Laurie Kovalenko, Tim Canty, and Ken Jucks
- The night mesospheric OH collaboration: Kancy Lee, Yuk Yung
- The solar proton event collaboration: Charles Jackman, Ray Roble