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The Estimated Climate Impact of the Hunga Tonga‐Hunga Ha'apai Eruption Plume

Geophysical Research Letters

September 2023
50(18)

DOI:10.1029/2023GL104634

License
CC BY 4.0

Authors:

Mark R. Schoeberl

Science and Technology Corp.

Yi Wang

Science and Technology Corporation

Andrew Dessler

Texas A&M University

Show all 6 authorsHide

On 15 January 2022, the Hunga Tonga‐Hunga Ha'apai (HT) eruption injected SO2 and water into the middle stratosphere. The SO2 is rapidly converted to sulfate aerosols. The aerosol and water vapor anomalies have persisted in the Southern Hemisphere throughout 2022. The water vapor anomaly increases the net downward IR radiative flux whereas the aerosol layer reduces the direct solar forcing. The direct solar flux reduction is larger than the increased IR flux. Thus, the net tropospheric forcing will be negative. The changes in radiative forcing peak in July and August and diminish thereafter. Scaling to the observed cooling after the 1991 Pinatubo eruption, HT would cool the 2022 Southern Hemisphere's average surface temperatures by less than 0.037°C.

Part a, OMPS‐LP measured AOD versus day number following the HT eruption in 2022. Crosses are the maximum AOD, blue crosses are the global average. A spacecraft anomaly resulted in missing measurements from late July to mid‐August. Black lines show linear fits to the data. Part b, changes in solar forcing with AOD for volcanic eruptions shown in Table 1. The loge fit Equation 1 is the thick solid line. Linear fits from H2002 and Table 1 data are shown as dashed and thin solid lines. The YH clear and cloudy fits are shown in blue and green lines. Volcanic events are small crosses next to the names. The red dot indicates HT (Part a, blue curve).

…

Part a, changes in stratospheric OMPS‐LP AOD versus time during 2022. Part b, change in solar forcing due to AOD using Equation 1. Part (c, d) shows the forcing using the YH kernels for clear sky and all skies. Vertical lines divide months with initial shown, dotted line is the latitude of HT, dashed line locates the equator.

…

Part a, 2022 zonal mean water vapor at 25 km. Part b, change in LWIR downward flux at the tropopause. Part c, change in SWIR downward flux at the tropopause. Note the sign change in the color bar. Part d, net flux change.

…

Part a, net radiative forcing using YH clear sky solar forcing (Figure 2c) and IR forcing change (Figure 3d). Part b, same as part a using YH all sky solar forcing. Black contours, 0, 0.5, 1.0, 1.5. Parts c, e show the components of the forcing versus latitude on 4/15/2022 and parts d, f for 12/1/2022, clear and all sky forcing. Part g shows hemispheric average and global average forcing, thick black line is global, red line is NH and thin line is SH, dashed lines for clear, and solid for all sky.

…

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1. Introduction

The Hunga Tonga-Hunga Ha'apai (HT) (20.54°S, 175.38°W) erupted on 15 January 2022, with a volcanic explo-

sivity index of five, comparable to eruption of Krakatau in 1883 (Carn etal.,2022, C22). As shown in Microwave

Limb Sounder (MLS) measurements (Millán etal.,2022, hereafter M22) and balloon sondes measurements

(Vomel etal.,2022), a significant amount of water vapor was injected into the tropical Southern Hemisphere

(SH) mid-stratosphere. HT also injected about 0.5Tg–1.5Tg of SO2 (C22, Sellitto etal.,2023) which produced

an aerosol layer that was detected by the Ozone Mapping and Profile Suite (OMPS) limb sounder (LP) (Taha

etal.,2022). Although SO2 injection was modest for an eruption of this size (C22; M22), the MLS estimated

water injection was 146Tg or ∼10% of the total stratospheric water vapor prior to the eruption (M22). The

water vapor and aerosol plumes from the HT eruption have persisted in the SH throughout 2022 (Schoeberl

etal.,2023). The stratospheric water vapor anomaly led to a mid-stratospheric cooling of ∼4° K in March-April

(Schoeberl etal.,2022, hereafter S22) due to the increased outgoing IR radiation.

Historically, the SO2 from large volcanic eruptions produces an abundance of aerosols that causes temporary

decrease in tropospheric temperatures due to the reduction in solar radiative forcing (Aurby etal.,2021; Hansen

etal.,2002; Stenchikov,2016; Yu & Huang,2023). Volcano-sourced sulfuric acid aerosols can persist for years

and even self-loft (Khaykin etal.,2022). Stratospheric aerosols reduce the direct solar flux and changes in surface

temperatures have been observed after large eruptions (Crutzen,2006; Fujiwara etal.,2020).

Changes in stratospheric water vapor can also contribute to changes in climate forcing (Forster & Shine,1999).

Solomon etal.(2010) estimated that the tropical, lower stratospheric decrease of ∼0.4ppmv H2O between 2000

and 2005 would reduce tropospheric forcing by ∼0.098W/m

2. This forcing results from changes in the long-wave

IR (LWIR) emission and short wave IR (SWIR) attenuation. Consistent with the Solomon etal.(2010) study,

Dessler etal.(2013) determined the sensitivity of the of the climate system to tropical stratospheric water vapor

and calculated a water vapor feedback parameter of 0.27W/m

2/ppmv.

Models predict that stratospheric H2O will increase as the climate warms. Basically, the tropical tropopause cold

trap warms allowing more water vapor into the stratosphere, although this effect is somewhat mitigated by the

Abstract On 15 January 2022, the Hunga Tonga-Hunga Ha'apai (HT) eruption injected SO2 and water

into the middle stratosphere. The SO2 is rapidly converted to sulfate aerosols. The aerosol and water vapor

anomalies have persisted in the Southern Hemisphere throughout 2022. The water vapor anomaly increases the

net downward IR radiative flux whereas the aerosol layer reduces the direct solar forcing. The direct solar flux

reduction is larger than the increased IR flux. Thus, the net tropospheric forcing will be negative. The changes

in radiative forcing peak in July and August and diminish thereafter. Scaling to the observed cooling after the

1991 Pinatubo eruption, HT would cool the 2022 Southern Hemisphere's average surface temperatures by less

than 0.037°C.

Plain Language Summary The Hunga Tonga-Hunga Ha'apai submarine volcanic eruption on 15

January 2022 produced aerosol and water vapor plumes in the stratosphere. These plumes have persisted mostly

in the Southern Hemisphere throughout 2022. Enhanced tropospheric warming due to the added stratospheric

water vapor is offset by the larger stratospheric aerosol attenuation of solar radiation. The change in the

radiative flux could result in a very slight cooling in Southern Hemisphere surface temperatures.

SCHOEBERL ETAL.

This is an open access article under

the terms of the Creative Commons

Attribution License, which permits use,

distribution and reproduction in any

medium, provided the original work is

properly cited.

The Estimated Climate Impact of the Hunga Tonga-Hunga

Ha'apai Eruption Plume

M. R. Schoeberl1 , Y. Wang1 , R. Ueyama2 , A. Dessler3 , G. Taha4 , and W. Yu5

1Science and Technology Corporation, Columbia, MD, USA, 2NASA Ames Research Center, Moffett Field, CA, USA,

3Texas A&M University, College Station, TX, USA, 4Morgan State University, Baltimore, MD, USA, 5Hampton University,

Hampton, VA, USA

Key Points:

• Following the January 2022

Hunga-Tonga eruption, both aerosols

and water vapor increased in the

stratosphere

• The stratospheric water vapor

increases the net downward radiative

flux up to 0.3W/m

2 and aerosols

reduce the solar flux up to ∼1.5W/m

• The reduction in radiative forcing

by the Hunga-Tonga eruption will

slightly cool the Southern Hemisphere

in 2022

Correspondence to:

M. R. Schoeberl,

mark.schoeberl@mac.com

Citation:

Schoeberl, M. R., Wang, Y., Ueyama,

R., Dessler, A., Taha, G., & Yu, W.

(2023). The estimated climate impact

of the Hunga Tonga-Hunga Ha'apai

eruption plume. Geophysical Research

Letters, 50, e2023GL104634. https://doi.

org/10.1029/2023GL104634

Received 20 MAY 2023

Accepted 25 AUG 2023

Corrected 5 OCT 2023

This article was corrected on 5 OCT

2023. See the end of the full text for

details.

Author Contributions:

Conceptualization: M. R. Schoeberl, Y.

Wang, A. Dessler

Data curation: G. Taha, W. Yu

Formal analysis: M. R. Schoeberl

Funding acquisition: M. R. Schoeberl,

R. Ueyama

Investigation: M. R. Schoeberl

Methodology: M. R. Schoeberl, Y. Wang,

A. Dessler, G. Taha

Software: M. R. Schoeberl, Y. Wang,

W. Yu

Supervision: R. Ueyama

Validation: M. R. Schoeberl, Y. Wang,

G. Taha

Visualization: M. R. Schoeberl

10.1029/2023GL104634

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strengthening Brewer-Dobson circulation (Xia etal., 2019). Banerjee et al. (2019) analyzing CMIP5 models

computed the stratospheric water vapor component of the climate feedback to be 0.14W/m

2/K for 4×CO2. Li

and Newman(2020) using the Goddard Earth Observing System Chemistry-Climate model computed a simi-

lar water vapor feedback value of 0.11W/m

2/K. A much smaller response (0.02–0.03W/m

2/K) was found by

Huang etal.(2016,2020). Note that these model studies are evaluating the long-term climate-system response

where non-atmospheric systems (e.g., the ocean, cryosphere) have time to equilibrate. The short-term atmos-

pheric response to sudden forcing changes may be larger because the system is out of equilibrium (Dessler &

Zelinka,2015).

Given the observed climate sensitivity to stratospheric water vapor (Dessler etal.,2013), it is logical to assume

that HT might have a climate impact. Jenkins etal. (2023) used a parameterized climate-response model to

investigate the impact of the HT water vapor plume. They neglected the impact of aerosols and only considered

the radiative forcing due to the water vapor. Jenkins etal.(2023) computed a 0.12W/m

2 increase in tropospheric

radiative forcing. M22 arrived at a similar number, 0.15W/m

2. On the other hand, Sellitto etal.(2023) and Zhu

etal.(2022) added the direct aerosol forcing and estimated that the plume would produce a peak forcing of −1 to

−2W/m

2. This exceeds the estimated H2O IR forcing. Clearly, both the net warming due to the H2O and cooling

due to the aerosol layer need to be considered.

In this study we extend the computation of the radiative forcing by Zhu etal.(2022) and Sellitto etal.(2022)

combining the H2O and aerosol radiative forcing. We compute the downward flux change due to stratospheric

water vapor using a radiative transfer model. Because of the complexity of computing the aerosol forcing, we

take a different approach to estimate the reduction in solar flux. We first use OMPS-LP measurements of strato-

spheric aerosol extinction to compute the stratospheric aerosol optical depth (AOD). We then convert the AOD

to changes in direct radiative forcing using a parameterization based on AOD estimates and direct forcing from

previous volcanic eruptions. This approach is also used in climate assessment models (e.g., Hansen etal.,2002,

hereafter H2002). To check our parameterization, we also use the aerosol direct radiative forcing parameteriza-

tion in Yu and Huang(2023) (hereafter YH). YH provides climatology kernels that can be used to convert AOD

to aerosol direct forcing under both clear and all sky (cloudy) conditions.

2. Data Sets

We use Microwave Limb Sounder (MLS) V5 for temperature and H2O measurements. The data quality for the

HT anomaly is detailed in M22 and MLS data is described in Livesey etal.(2021). We restrict our constituent

analysis to below 35km, which is roughly the maximum height of the plume a few weeks after the eruption.

We use the aerosol extinction data from OMPS-LP, level-2 V2.1. The V2.1 data (Taha etal.,2022) provides the

most accurate OMPS-LP aerosol retrieval up to 36km. Although the extinction measurements by OMPS-LP

are generally consistent with those made by SAGE III/ISS, the OMPS-LP algorithm may overestimate the aero-

sol extinction below the aerosol peak (Bourassa etal.,2023). AOD is computed from OMPS-LP extinction at

600nm by integrating the extinction from 36km to the tropopause height included in the OMPS-LP files. The

AOD is converted from 600 to 550nm assuming an Ångstrom exponent of 1.0 which was derived from SAGE

III/ISS HT observations (Taha etal.,2022). The daily MLS and OMPS data sets are averaged onto a 5°×10°

latitude-longitude grid.

We show the SO2 eruption data available from the NASA Multi-Satellite Volcanic Sulfur Dioxide L4 Long-Term

Global Database produced as part of the NASA MEaSUREs project (Carn etal.,2016).

3. Analysis

In the sections below, we describe our approach to estimating the changes in tropospheric forcing due to HT

aerosols and stratospheric water vapor.

3.1. Parameterization of the Direct Solar Radiative Forcing by Aerosols

Figure1a shows the variations in OMPS-LP AOD during 2022; both the maximum AOD and global average

AOD are shown. The figure shows a rapid increase in maximum AOD following the eruption which is followed

Writing – original draft: M. R.

Schoeberl

Writing – review & editing: Y. Wang, R.

Ueyama, A. Dessler, G. Taha, W. Yu

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by a slower growth rate until mid-April. Anomalies and gaps in the late July and early August data are due to a

spacecraft anomaly. Although the peak AOD reaches 0.05, the global average AOD only reaches ∼0.02 because

most of the aerosol stays within the SH (S22; Taha etal.,2022). Simulations by Zhu etal.(2022) show that SO2

is converted to sulfate aerosols rapidly following the eruption—a process enhanced by the abundance of water

vapor in the plume. After mid-April, dispersion of the aerosols combined with settling cause a slow decrease from

the maximum AOD.

H2002 assumed that the aerosol driven change in the direct solar radiative forcing (∆A) can be approximated by

∆A=−RAOD, R=21. Yu etal.(2023) used a similar relation to account for ∆A due to volcanoes and smoke

and found R=∼23. YH derived direct radiative forcing kernel maps from reanalysis to convert AOD to ∆A, but

avoided large volcanic eruption periods. The YH global average clear sky conversion factor R is 29.4, and for all

skies, R=15.7.

The stratospheric AOD changes associated with volcanic eruptions can be much larger than the observed AOD

perturbations in the 2000–2022 period YH analyzed. We therefore have independently derived our own param-

eterization from volcanic analyses. Table1 shows a list of major observed eruptions and one simulated eruption

(Aubry etal.,2021) along with their estimated SO2 emission, the maximum globally averaged AOD, and the

maximum global direct forcing (ΔΑ W/m

2). Using these AOD values and our estimates, we can compute the

HT direct forcing. We set the background stratospheric AOD is set to 0.012 which is an offset since we want to

Figure 1. Part a, OMPS-LP measured AOD versus day number following the HT eruption in 2022. Crosses are the maximum AOD, blue crosses are the global

average. A spacecraft anomaly resulted in missing measurements from late July to mid-August. Black lines show linear fits to the data. Part b, changes in solar forcing

with AOD for volcanic eruptions shown in Table1. The loge fit Equation1 is the thick solid line. Linear fits from H2002 and Table1 data are shown as dashed and thin

solid lines. The YH clear and cloudy fits are shown in blue and green lines. Volcanic events are small crosses next to the names. The red dot indicates HT (Part a, blue

curve).

Eruption Date SO2 (Tg) Max AOD ΔΑ W/m

2loge fit ΔΑ W/m

2YH ΔΑ W/m

2 clear/cloudy References

Agung May 1963 12 0.11 −2.9 −2.8 −3.2/−1.7 Pitari etal.(2016)

El Chichón April 1982 7 (8) 0.05 −1.75 −1.8 −1.4/−0.78 Pitari etal.(2016)

Nevado del Ruiz November 1985 1.2 (0.7) 0.015 −0.3 −0.29 −0.44/−0.23 Pitari etal.(2016)

Pinatubo June 1991 20 (17) 0.2 −3.5 −3.55 −5.88/−3.14 Pitari etal.(2016)

Raikoke June 2019 (1.4) 0.016 −0.4 −0.41 −0.48/−0.26 Kloss etal.(2021)

Lg. Erup.Sim. - 10 0.15 −3.2 −3.2 −4.4/−2.3 Aubry etal.(2021)

Hunga-Tonga January 2022 (0.5–1.5) 0.018 −0.64 −0.59/−0.31 This paper

Note. We also show the change in direct forcing Equation1 and the YH parameterization. We use the Raikoke AOD maps shown in Kloss etal.(2021) to estimate

the Raikoke AOD. SO2 amounts used by the authors shown; amounts in parenthesis are from the NASA database, Carn etal.(2022), and Sellitto etal.(2023) for HT.

Table 1

Estimated Emission SO2, the Maximum Globally Averaged AOD (550nm) and Decrease in Global Solar Flux for the Indicated Large Volcanic Events

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compute ΔA(volcaniconly). Figure1b shows the estimated change in solar flux, ΔA, versus AOD for the data in

Table1 with each volcano listed. We also show a linear fit and loge(AOD) fit to volcanic AOD, H2002 param-

eterization, and both YH parameterizations. We find R=19.5 for our linear fit, which is close to the H2002 R

value of 21 and the Yu etal.(2023) R value of 23. Figure1b shows that the loge fit better reproduces the estimated

changes in ΔA compared to the linear fit. The loge fit is

=−

(

5.58+1.26 log(AOD

)

) W∕m

(1)

Table1 also shows that YH clear sky parameterization produces a result very close to the results using Equation1.

3.2. Radiative Forcing Changes Due To Hunga-Tonga

3.2.1. Changes in Direct Solar Forcing Due To Aerosols

For the maximum HT global average AOD value of 0.02, (1) gives a peak global decrease in solar flux (ΔA)

of −0.64W/m

2 (Figure1b, red dot; Table1). Using the H2002 parameterization we estimate the change is

−0.42W/m

2. The YH parameterization gives −0.54W/m

2 for clear skies and −0.29W/m

2 for all skies. Zhu

etal.(2022)'s estimate of −0.25W/m

2 is slightly lower, because they averaged the forcing in February before the

peak AOD in March-April and their simulated aerosol cloud is less extensive than that observed by OMPS-LP

(their Figure 3).

Figure 2a shows the surface area weighted zonal mean AOD and aerosol solar radiative forcing due to HT

(Figure2b) from Equation1. Although Equation1 is derived using global averages, there is no reason to believe

it would not be valid for local changes in solar flux because the approximation simply links stratospheric AOD

directly to solar flux. As a check on this assumption, we also perform the calculation using YH kernel maps and

these calculations are also shown in Figures2c and2d. Our parameterization and YH clear sky are nearly iden-

tical, suggesting that YH can be extended to volcanic events the size of HT. Figure2d shows that if clouds are

included the direct solar decreases by about a factor of ∼2. From hereafter we will use the YH parameterization.

The evolution of the direct solar forcing follows the spatial changes in AOD as might be expected, and the

decrease in solar forcing is mostly confined to the SH. Our estimates of solar flux changes are in good agreement

with estimates by Sellitto etal.(2022). Figure2 also shows a southward shift in the aerosol distributions near

day 150 (May 30), and this is reflected in changes in forcing. Sellitto etal.(2023) also shows this southward shift

(their Figure 1b).

3.2.2. Changes in IR Radiative Forcing Due To Water Vapor

HT produced an enhanced, mostly SH, stratospheric water vapor layer that mostly extends between 22 and

30km. This layer generates additional downward LWIR flux and also slightly reduces the solar flux due to water

vapor radiative absorption in the SWIR bands. We use the radiative transfer model (RTM) described by Mlawer

etal.(1997) to compute the downward radiative flux changes produced by this layer using MLS observed trace

gases and temperatures.

To quantify the flux changes, we first compute a daily climatology of MLS temperature and trace gases using

2016–2021 data. We calculate the difference between the 2022 downward tropopause fluxes and the downward

fluxes computed using the climatology. We have not applied any adjustment to temperature (e.g., fixed dynamical

heating) due to water vapor cooling in the radiative forcing calculations, as was done in previous work (Dessler

etal.,2013; Solomon etal.,2010). Solomon etal.(2010) shows that the instantaneous forcing and adjusted forc-

ing are very similar above 22km. Since HT's water vapor was mostly injected above that altitude, the adjustment

is unimportant. Jenkins etal.(2023) also did not perform a temperature adjustment in their estimate of HT's

LWIR radiative forcing.

Figure3a shows the 25km zonal mean MLS water vapor versus latitude. Figure3b shows the instantaneous

tropopause downward LWIR flux change due to the observed H2O distribution, ΔLWIR. In Figures3b–3d, the

latitude range is restricted because the flux estimates at the poles are very noisy due to tropopause fluctuations.

Figure3c shows ΔSWIR due to the attenuation of water vapor (note the sign change in the color bar). Figure3d

shows the net change in H2O radiative forcing ΔLWIR+ΔSWIR. The changes in the downward radiative flux

follow the evolution of the stratospheric water vapor distribution. There is a small northward shift in aerosols and

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water vapor shortly after the eruption, and an additional small northward shift of the water vapor distribution in

April associated with the QBO (Schoeberl etal.,2023).

The question remains: how much of the LWIR forcing increase is due to H2O and how much is due to the

temperature differences between 2022 and the climatology? To quantify this, we take the 2016–2021 temperature

climatology and substitute the 2022 water vapor. We also and take the 2022 temperature field and substitute in the

2016–2021 water vapor climatology. These two experiments help isolate the impact of the HT water vapor from

natural temperature fluctuations. We find that about 1/3 of the 2022 LWIR flux increase through April is due to

the descending QBO thermal anomaly and 2/3 is due to the stratospheric water vapor increase.

3.2.3. Net Radiative Forcing Changes

Figure4 a,b show the time series of the net change in radiative forcing (ΔLWIR+ΔSWIR+ΔA) using the YH

clear and all sky parameterizations for ΔA. We also show two latitude cross sections on April 15 (Figures4c

and4e) and 1 December 2022 (Figures4d and4e). For both clear and all sky ΔA estimates, the aerosol direct

forcing overwhelms the heating from stratospheric water vapor. Figure4g shows the hemispheric and global

average forcing time series. The total SH radiative forcing peaks in June/July. On the other hand, the much smaller

Northern Hemisphere (NH) forcing peaks in April/May after the QBO has spread aerosols and trace gases into

the NH (Schoeberl etal.,2023).

Figure 2. Part a, changes in stratospheric OMPS-LP AOD versus time during 2022. Part b, change in solar forcing due to AOD using Equation1. Part (c, d) shows the

forcing using the YH kernels for clear sky and all skies. Vertical lines divide months with initial shown, dotted line is the latitude of HT, dashed line locates the equator.

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The climate impact of the HT eruption plume is difficult to estimate since the aerosol and water vapor forcing

decreases by more than half from the peak in mid-April to mid-December (Figure4d) so the overall HT forcing

is transient. However, we can crudely estimate the tropospheric surface temperature response for a transient

event using the analyses of the short-term temperature changes due to stratospheric aerosol loading following the

Pinatubo eruption. For Pinatubo, Fujiwara etal.(2020) estimated a tropospheric surface temperature decrease

of ∼0.15°C in the years following the eruption due to an average optical depth of ∼0.1 (see their Figure A3).

For our estimate, we only consider the shortwave components; the enhanced LWIR is absorbed in the upper

troposphere and will not directly affect the surface temperature (Sellitto etal.,2022; Wang & Huang,2020).

The SH 2022 clear sky average radiative forcing sans the LWIR component is −0.67 W/m

2. Scaling this

forcing to Pinatubo, we roughly estimate that the HT 2022 average SH surface temperature change would be

−0.67 (0.15◦∕2.67) = −0.037◦C.

Using the YH all sky parameterization, the SH temperature change would be

−0.025°C. Note that Fujiwara etal.(2020)'s estimate of the Pinatubo surface temperature response is about five

times smaller than earlier estimates found in Crutzen(2006). A thermal response this small would be barely

detectable against background meteorological variability. We are also neglecting second order climate responses

that could occur, such as changes in cloudiness or lapse rate.

4. Summary and Discussion

The Hunga-Tonga-Hunga Ha'apai (HT) eruption produced increased stratospheric water vapor and aerosols

primarily in the Southern Hemisphere. Jenkins et al. (2023) suggested that the increased stratospheric water

vapor would warm the climate slightly, but their study neglected the role of volcanic aerosols in reducing the

solar flux. We use a radiative transfer model to estimate the changes in downward IR flux due to the MLS

observed enhanced water vapor layer, and OMPS-LP data to compute the stratospheric AOD. We parameterize

Figure 3. Part a, 2022 zonal mean water vapor at 25km. Part b, change in LWIR downward flux at the tropopause. Part c, change in SWIR downward flux at the

tropopause. Note the sign change in the color bar. Part d, net flux change.

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Figure 4. Part a, net radiative forcing using YH clear sky solar forcing (Figure2c) and IR forcing change (Figure3d). Part b, same as part a using YH all sky solar

forcing. Black contours, 0, 0.5, 1.0, 1.5. Parts c, e show the components of the forcing versus latitude on 4/15/2022 and parts d, f for 12/1/2022, clear and all sky

forcing. Part g shows hemispheric average and global average forcing, thick black line is global, red line is NH and thin line is SH, dashed lines for clear, and solid for

all sky.

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the reduction in solar flux due to HT aerosols using past volcanic events (Table1). Our results are nearly identical

to Yu and Huang(2023) results for clear skies, non-volcanic conditions. We subsequently use their clear and all

sky parameterizations to assess the direct solar forcing. The solar flux reduction by aerosols is larger than the net

IR flux increase due to stratospheric water vapor. In other words, the direct solar radiative cooling associated with

the HT aerosols overwhelms the enhanced thermal radiation from stratospheric water vapor plume. Our results

are in good agreement with net radiative forcing changes estimated by Sellitto etal.(2022) and Zhu etal.(2022).

We find that the zonal mean peak change in net radiative forcing occurs in May 2022, but the SH average forcing

peaks in June/July as the constituents spread throughout the SH. Using the observed impact on tropospheric

temperatures from Pinatubo as a scale, Hunga-Tonga would produce an SH annual average surface temperature

change of less than −0.038°C for clear skies and −0.021°C for all skies.

Data Availability Statement

The RTM used to estimate H2O IR cooling rates is from Atmospheric and Environmental Research

(RTE+RRTMGP) and can be freely downloaded at http://rtweb.aer.com/rrtm_frame.html. OMPS-LP data, Taha

etal.(2021), is available at https://disc.gsfc.nasa.gov/datasets/OMPS_NPP_LP_L2_AER_DAILY_2/summary,

https://doi.org/10.5067/CX2B9NW6FI27. The algorithm is documented in Taha etal.(2021). SO2 historical

volcanic eruption data is available at the NASA disc https://disc.gsfc.nasa.gov/datasets/MSVOLSO2L4_4/

summary. Aura MLS Level 2 data, Livesey etal.(2021) JPL D-33509 Rev. C, is available at https://disc.gsfc.

nasa.gov/datasets?page=1&keywords=AURA%20MLS.

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This work was supported under

NASA Grants NNX14AF15G,

80NSSC21K1965, and 80NSSC20K1235.

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Erratum

The originally published version of this article contained a typographical error in a reference. Sellitto etal.

(2022) was incorrectly published as Silletto etal. (2022) in both the reference list and the in-text citations. The

incorrect reference appeared in the first sentence of the last paragraph of the Introduction; the second sentence

of the last paragraph of Section 3.2.1; the fourth sentence of the last paragraph of Section 3.2.3; and the ninth

sentence of Section 4. The errors have been corrected, and this may be considered the authoritative version of

record.

Long-Term Climate Impacts of Large Stratospheric Water Vapor Perturbations

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Dec 2024

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PHOTOCH PHOTOBIO SCI

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Volcanic and wildfire events between 2014-2022 injected ~3.2 Tg of sulfur dioxide and 0.8 Tg of smoke aerosols into the stratosphere. With injections at higher altitudes and lower latitudes, the simulated stratospheric lifetime of the 2014-2022 injections is about 50% longer than the volcanic 2005-2013 injections. The simulated global mean effective radiative forcing (ERF) of 2014-2022 is -0.18 W m-2, ~40% of the ERF of the period of 1991-1999 with a large-magnitude volcanic eruption (Pinatubo). Our climate model suggests that the stratospheric smoke aerosols generate ~60% more negative ERF than volcanic sulfate per unit aerosol optical depth. Studies that fail to account for the different radiative properties of wildfire smoke relative to volcanic sulfate will likely underestimate the negative stratospheric forcings. Our analysis suggests that stratospheric injections offset 20% of the increase in global mean surface temperature between 2014-2022 and 1999-2002.

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Feb 2023
GEOPHYS RES LETT

On 15 January 2022, the Hunga Tonga‐Hunga Ha'apai (HT) eruption injected SO2 and water into the middle stratosphere. Shortly after the eruption, the water vapor anomaly moved northward toward and across the equator. This northward movement appears to be due to equatorial Rossby waves forced by the excessive infrared water vapor cooling. Following the early eruption stage, persistent mid‐stratospheric water vapor and aerosol layers were mostly confined to Southern Hemisphere tropics (Eq. to 30°S). However, during the spring of 2022, the westerly phase of the tropical quasi‐biennial oscillation (QBO) descended through the tropics. The HT water vapor and aerosol anomalies were observed to again move across the equator coincident with the shift in the Brewer‐Dobson circulation and the descent of the QBO shear zone.

Distributions and Trends of the Aerosol Direct Radiative Effect in the 21st Century: Aerosol and Environmental Contributions

Article

Full-text available

Feb 2023

The aerosol direct radiative effect (ADRE) is controlled by both aerosol distributions and environmental factors, making it interesting and important to quantitatively assess their effects on the ADRE inhomogeneity and climate trends. By analyzing the ADRE in the 21st century from a global reanalysis data set, we find that the spatial variability of the ADRE and its trends can be well explained by a linear regression model. In this model, scattering and absorbing aerosol optical depths (AODs) are used, along with critical environmental variables such as surface albedo and cloud radiative effect, as predictors. Based on this model, we find that approximately 70% of the ADRE inhomogeneity is due to the AOD distributions and the remainder is attributable to environmental factors. This study also shows that a stronger cooling effect of the scattering aerosols in the Northern Hemisphere drives northward cross‐equator meridional energy transport, although this transport exhibits a declining trend over the last two decades. The changes in surface albedo and cloud radiative effect strongly influence the trends in the regional ADRE and the meridional energy transport driven by them. In particular, the reduction of surface albedo (sea ice) is primarily responsible for the enhancement of the cooling ADRE, as well as an associated trend in meridional energy transport, in the Arctic.

Tomographic Retrievals of Hunga Tonga‐Hunga Ha'apai Volcanic Aerosol

Article

Full-text available

Feb 2023
GEOPHYS RES LETT

The 2022 eruption of the Hunga Tonga‐Hunga Ha'apai volcano caused substantial impacts on the atmosphere, including a massive injection of water vapor, and the largest increase in stratospheric aerosol for 30 years. The Ozone Mapping and Profiler Suite (OMPS) Limb Profiler instrument has been critical in monitoring the amount and spread of the volcanic aerosol in the stratosphere. We show that the rapid imagery from the OMPS instrument enables a tomographic retrieval of the aerosol extinction that reduces a critical bias of up to a factor of two, and improves vertical structure and agreement with coincident lidar and occultation observations. Due to the vertically thin and heterogeneous nature of the volcanic aerosol, this impacts integrated values of aerosol across latitude, altitude, and time for several months. We also investigate the systematic impact of uncertainty in assumed particle size that result in an underestimation of the aerosol extinction at the peak of the volcanic aerosol layer.

Tonga eruption increases chance of temporary surface temperature anomaly above 1.5 °C

Article

Full-text available

Jan 2023
Nat. Clim. Change.

On 15 January 2022, the Hunga Tonga–Hunga Ha’apai (HTHH) eruption injected 146 MtH2O and 0.42 MtSO2 into the stratosphere. This large water vapour perturbation means that HTHH will probably increase the net radiative forcing, unusual for a large volcanic eruption, increasing the chance of the global surface temperature anomaly temporarily exceeding 1.5 °C over the coming decade. Here we estimate the radiative response to the HTHH eruption and derive the increased risk that the global mean surface temperature anomaly shortly exceeds 1.5 °C following the eruption. We show that HTHH has a tangible impact of the chance of imminent 1.5 °C exceedance (increasing the chance of at least one of the next 5 years exceeding 1.5 °C by 7%), but the level of climate policy ambition, particularly the mitigation of short-lived climate pollutants, dominates the 1.5 °C exceedance outlook over decadal timescales.

Unexpected self-lofting and dynamical confinement of volcanic plumes: the Raikoke 2019 case

Article

Full-text available

Dec 2022

Recent research has provided evidence of the self-lofting capacity of smoke aerosols in the stratosphere and their self-confinement by persistent anticyclones, which prolongs their atmospheric residence time and radiative effects. By contrast, the volcanic aerosols—composed mostly of non-absorptive sulphuric acid droplets—were never reported to be subject of dynamical confinement. Here we use high-resolution satellite observations to show that the eruption of Raikoke volcano in June 2019 produced a long-lived stratospheric anticyclone containing 24% of the total erupted mass of sulphur dioxide. The anticyclone persisted for more than 3 months, circumnavigated the globe three times, and ascended diabatically to 27 km altitude through radiative heating of volcanic ash contained by the plume. The mechanism of dynamical confinement has important implications for the planetary-scale transport of volcanic emissions, their stratospheric residence time, and atmospheric radiation balance. It also provides a challenge or “out of sample test” for weather and climate models that should be capable of reproducing similar structures.

The unexpected radiative impact of the Hunga Tonga eruption of 15th January 2022

Article

Full-text available

Nov 2022

The underwater Hunga Tonga-Hunga Ha-apai volcano erupted in the early hours of 15th January 2022, and injected volcanic gases and aerosols to over 50 km altitude. Here we synthesise satellite, ground-based, in situ and radiosonde observations of the eruption to investigate the strength of the stratospheric aerosol and water vapour perturbations in the initial weeks after the eruption and we quantify the net radiative impact across the two species using offline radiative transfer modelling. We find that the Hunga Tonga-Hunga Ha-apai eruption produced the largest global perturbation of stratospheric aerosols since the Pinatubo eruption in 1991 and the largest perturbation of stratospheric water vapour observed in the satellite era. Immediately after the eruption, water vapour radiative cooling dominated the local stratospheric heating/cooling rates, while at the top-of-the-atmosphere and surface, volcanic aerosol cooling dominated the radiative forcing. However, after two weeks, due to dispersion/dilution, water vapour heating started to dominate the top-of-the-atmosphere radiative forcing, leading to a net warming of the climate system.

Perturbations in stratospheric aerosol evolution due to the water-rich plume of the 2022 Hunga-Tonga eruption

Article

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Oct 2022

The January 2022 Hunga Tonga-Hunga Ha’apai volcanic eruption injected a relatively small amount of sulfur dioxide, but significantly more water into the stratosphere than previously seen in the modern satellite record. Here we show that the large amount of water resulted in large perturbations to stratospheric aerosol evolution. Our climate model simulation reproduces the observed enhanced water vapor at pressure levels ~30 hPa for three months. Compared with a simulation without a water injection, this additional source of water vapor increases hydroxide, which halves the sulfur dioxide lifetime. Subsequent coagulation creates larger sulfate particles that double the stratospheric aerosol optical depth. A seasonal forecast of volcanic plume transport in the southern hemisphere indicates this eruption will greatly enhance the aerosol surface area and water vapor near the polar vortex until at least October 2022, suggesting that there will continue to be an impact of this eruption on the climate system.

Analysis and Impact of the Hunga Tonga‐Hunga Ha'apai Stratospheric Water Vapor Plume

Article

Full-text available

Oct 2022
GEOPHYS RES LETT

On 15 January 2022, the Hunga Tonga‐Hunga Ha'apai eruption injected SO2 and H2O into the middle stratosphere. The eruption produced a persistent mid‐stratospheric sulfate aerosol and H2O layer mostly confined to Southern Hemisphere (SH) tropics (Eq. to 30°S). These layers are still present in the tropics 5½ months after the eruption. The SH tropical confinement is simulated using a trajectory model. Measurements following the eruption show that the H2O layer is slowly rising while the aerosol layer is descending. The H2O layer's upward movement is consistent with the residual vertical velocity. Gravitationally settling explains the descent of the aerosol layer. A −4 K temperature anomaly coincident with the H2O enhancement is observed and is caused by thermal adjustment to the additional H2O IR cooling. A simple model of volcanic water injection at the time of the eruption simulates the observed vertical distribution H2O.

Observing the SO2 and Sulphate Aerosol Plumes from the 2022 Hunga Tonga-Hunga Ha'apai Eruption with IASI

Preprint

Aug 2023

The Hunga Tonga-Hunga Ha’apai volcano violently erupted on 15 January 2022, producing the largest perturbation of the stratospheric aerosol layer since Pinatubo 1991, despite the estimated modest injection of SO2. Here we present novel SO2 and sulphate aerosol (SA) co-retrievals from the Infrared Atmospheric Sounding Instrument, and use them to study the dispersion of the Hunga Tonga plume over the entire year 2022. We observe rapid conversion of SO2 (e-folding time: 17.1±0.6 days) to sulphate aerosols (SA), with an initial injected burden of >1.0 Tg. This points at larger SO2 injections than previously thought. A long-lasting SA plume was observed, with a meridional dispersion of marked anomalies from the tropics to the higher southern hemispheric latitudes. A very small SA removal is observed after 1-year dispersion. The total SA mass burden was estimated at 1.6 ± 0.1 Tg in total column, with a build-up e-folding time of about 2 months.