INitricacidinthestratosphereandthesoundingoftheEarth’satmo-sphere Contents

Contents

General introduction and objectives

I

Nitric acid in the stratosphere and the sounding of the Earth’s

atmo-sphere

1 A few reminders

1.1 The Earth’s atmosphere . . . . 1.1.1 Vertical structure . . . . 1.1.2 Chemical composition . . . . 1.1.3 General circulation . . . . 1.1.4 Current concerns for the atmosphere . . . . 1.2 Sounding the atmosphere . . . . 1.2.1 Active and passive sounding . . . . 1.2.2 Observation geometries . . . . 2 Chemistry and dynamics of the stratosphere

2.1 The stratosphere . . . . 2.1.1 Structure and chemical composition . . . . 2.1.2 Circulation and dynamics . . . . 2.1.3 The polar stratosphere . . . . 2.2 Nitric acid in the stratosphere . . . . 2.2.1 Sources and sinks . . . . 2.2.2 Polar Stratospheric Clouds . . . . 2.3 Ozone in the stratosphere . . . . 2.3.1 The Chapman mechanism . . . . 2.3.2 Catalytic ozone loss . . . . 2.4 Antarctic ozone hole . . . . 2.4.1 Mechanisms for polar O3 depletion . . . .

2.4.2 Current state of the ozone layer . . . . 3 Radiative transfer in the thermal infrared

3.1 Reminders and definitions . . . . 3.1.1 Electromagnetic energy . . . . 3.1.2 Flux, intensity and solid angle . . . . 3.1.3 Blackbody radiation and emissivity . . . . 3.1.4 Interaction between atmospheric gases and radiation . . . . 3.2 Radiative transfer in the TIR . . . . 3.2.1 The Schwarzschild equation . . . .

2 CONTENTS 3.2.2 Radiative transfer applied to the atmosphere . . . . 3.3 Retrieving the atmosphere’s composition . . . . 3.3.1 Inverse problem . . . . 3.3.2 Optimal estimation method . . . . 3.3.3 Characterization of the solution . . . . 4 Measuring the Earth’s stratosphere

4.1 A review of the measurements of the stratosphere . . . . 4.2 Measurements of HNO3 in the stratosphere . . . .

4.3 The IASI instrument . . . . 4.3.1 Characteristics and measurements . . . . 4.3.2 Fast Optimal Retrievals on Layers for IASI . . . .

II

Characterization, evaluation and validation of the IASI-retrieved HNO

profiles and columns

5 Characterization, validation, and comparisons with models

5.1 Characterizing FORLI-HNO3 . . . .

5.1.1 Profiles and vertical sensitivity . . . . 5.1.2 Error budget . . . . 5.2 Validating FORLI-HNO3 . . . .

5.2.1 The NDACC network and the FTIR instruments . . . . 5.2.2 Validation methodology: colocation criteria and smoothing . . . . 5.2.3 Profiles and time series comparisons . . . . 5.3 Comparison with models . . . . 5.3.1 IASI vs NIWA-UKCA . . . . 5.3.2 IASI vs BASCOE . . . .

III

HNO

spatial and temporal variability

6 10 years of IASI HNO3 measurements

6.1 HNO3 global distributions . . . .

6.2 HNO3 time series . . . .

6.2.1 Technical note: equivalent latitudes . . . . 6.2.2 Annual and interannual HNO3 variability . . . .

7 Denitrification and polar processes in Antarctica

7.1 HNO3 - temperature regimes in the polar stratosphere . . . .

7.2 Onset of the HNO3 depletion and "drop" temperature detection . . . .

7.2.1 Potential vorticity time series . . . . 7.2.2 Global distribution of denitrification temperatures . . . . 7.2.3 Discussion . . . .

IV

Understanding HNO

and O

variability in the stratosphere

8 Fitting the observations with a regression model

CONTENTS 3 9 Mulivariate regressions applied to HNO3

9.1 HNO3 fits for equivalent latitude bands . . . .

9.1.1 Matches and mismatches . . . . 9.1.2 Focus on the polar regions and the influence of VPSC . . . . 9.2 Global model assessment with regard to the HNO3variability . . . .

9.3 Global patterns of fitted parameters . . . . 9.4 What could explain the remainder of HNO3 variability? . . . .

9.4.1 Lightning activity . . . . 9.4.2 Vegetation fires . . . . 10 Multivariate regressions applied to O3

10.1 O3time series . . . .

10.2 O3fits for equivalent latitude bands . . . .

10.3 Global model assessment with regard to the O3 variability . . . .