Estimating Multi-Decadal Cirrus Cloud Topof-the-Atmosphere Climate RadiativeForcing Trends Across the Warming Arctic
James R. Campbell & Erica K. Dolinar
US Naval Research Laboratory (NRL), Monterey, CA, USA
Theodore M. McHardy – American Society for Engineering Education (ASEE)/NRL, Monterey, CA

Jared W. Marquis – Univ. of North Dakota, Department of Atmospheric Sciences, Grand Fork, ND, USA
Simone Lolli – Consiglio Nazionale delle Ricerche, Istituto di Metodologie per l’Analisi Ambientale, Tito Scalo, Italy
Jasper R. Lewis – Univ. of Maryland Baltimore County c/o NASA Goddard Space Flight Center, Greenbelt, MD, USA
Ellsworth J. Welton – NASA Goddard Space Flight Center, Greenbelt, MD, USANASAMPLNET

EarthCARE Science and Validation Workshop
Frascati, Italy
14 November 2023

Motivation and Perspective• Cirrus clouds are the most common cloudtype (global occurrence rate of ~40%)• Net cloud radiative forcing (CRF; thedifference in clear-sky vs. cloudy radiationbudget) magnitude and sign change as afunction of IWP (or optical depth)• Cirrus are the only cloud type to induce +/TOA forcing during daytime• The Polar regions are particularly sensitive toclimate change, due to the combination of rapid
sea ice (i.e., surface albedo) decline and overallwarming

Tropical TTL cirrus (Berry and Mace 2014)
CloudSat/CALIPSO

frequency• Clouds derived from extended satellite
lidar/radar records have proven fundamental
for diagnosing significant changes to theplanetary radiative budget

In this study, we seek to estimate changes
to top-of-the-atmosphere (TOA) energybalance in the Arctic induced by cirrus
clouds over the last forty years| 2What Influences the Daytime Cirrus Cloud Radiative Forcing?
UPWELLING IR

REFLECTEDSOLAR
2. CLOUD T
3. EFFECTIVE RADIUS
4. SPECTRAL
EXTINCTION &SINGLE-SCATTERALBEDO

1. SOLAR ZENITH ANGLEREFLECTEDSOLAR

UPWELLING IR

RE-EMITTED IR

DOWNWELLING
SOLAR

RE-REFLECTEDSOLAR

5. SURFACE T
6. SURFACE ALBEDO
No other region is experiencing as drastic a change in surface albedo as the Arctic and its declining summer sea ice| 3| 3

Experiment Setup & Definitions

More details at Poster 12

RadiativeTransfer Model

Meteorology &Surface Albedo

Cloud Heights

TemporalFrequency

CODIce Crystal
Effective Size

Optical Model

Fu-Liou-Gu;
broadband, 1-D

MERRA-2(0.5° × 0.625°)

CALIOP monthly
average; 15-year
climo (5° × 5°)*Once per month**;5-yr increments

0.03 – 3.0(22 values)

Dolinar et al. (2022)

8-element column
aggregates****cirrus definition = transparent (index 7 and 8); cloud optical depth (COD) < 3.0 and cloud top temperature < –37 °C
CALIOP Collection: CAL_LID_L2_05kmCPro-Standard-V4-20**select the 15th day of each month; use solar geometry consistent with daytime average CRF***severely roughened ice crystal model (Yang et al. 2013; Bi and Yang 2014; 2017)

TOTAL FLUX (W·m–2)

Daytime Definition• Time of day when the CRF can be +/• Total Flux (@ TOA) = incoming solar – outgoing (solar + IR)• Offline calculation: Clear-sky flux computed fromclimatology (e.g., temperature, water vapor)• Daytime = total flux > 0• Daytime fraction @ Latitude 71.5 °N (left image)• June – 0.61 ; September – 0.28; February – 0.00

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Changes in Arctic Surface Albedo (1980 – 2020)
2020

TrendSurface Albedo

1980

Nighttime area contained within black contour

Domain average(bottom)• Arctic sea ice
loss drives theoverall decreasein surfacealbedo• Some regions
have become
10% darker
since 1980
• Some regions
show anincrease inalbedo| 5Solving Absolute Daytime TOA Net CRF
Absolute TOA net CRF (W·m–2) =𝐶𝑅𝐹 𝑙𝑎𝑡, 𝑙𝑜𝑛, 𝐶𝑂𝐷, 𝑚𝑜𝑛𝑡ℎ, 𝑦𝑒𝑎𝑟 × 𝐶𝐹 𝑚𝑜𝑛𝑡ℎ × 𝐷𝐹 𝑙𝑎𝑡, 𝑙𝑜𝑛, 𝑚𝑜𝑛𝑡ℎ× 𝑅𝐹 𝐶𝑂𝐷, 𝑚𝑜𝑛𝑡ℎ × 𝐷𝐴𝐹(𝑚𝑜𝑛𝑡ℎ)June 1980

WARMING
COOLING• TOA Net CRF (COD = 0.9)
• Daytime area fraction (DAF)
outside of white contour• Cloud Fraction (CF) – CALIOP (15year mean)• Daytime Fraction (DF)• COD relative frequency (RF)distribution• TOA Net CRF as a function of COD• Each point represents thedomain-average TOA net CRF at agiven COD| 6

40-Years of Arctic Cirrus Daytime TOA Net CRF
Left column – 1980 estimate
Right column – trend (W·m–2 /40-yr)
Grey shade – 2020 nighttime area

April CRF is relatively
stable and near 0 W/m2
June CRF switches
sign and its trend isstrongest among allmonthsEnhanced cooling inJuly and August as
sea-ice minimums
grow more extreme| 7

Parameter

Trend Magnitude

Notable Trends in Arctic Cirrus Radiative Properties
TrendAlbedo
Nighttime Fraction
Daytime CRF

Nighttime CRF

1980

02020
MAY
•

•

Nighttime fraction has been increasing since 1980 duringmonths prior to melt onset, indicating an enhancement ofnighttime cirrus warming
Decrease in nighttime fraction during months of sea ice
melt coincides with enhancement in daytime cooling| 8Summary• The Arctic has warmed at an alarming pace over the last fortyyears. However, cirrus clouds are acting to increasingly cool theregion during daylit hours, driven by sea-ice reduction andsuppressing of the albedo-driven warming.
• We’ve also discovered that ‘Radiative Polar Night’ conditions
are actually increasing prior to the melt season due to regionalwarming. Overall cirrus cooling is still occurring, however, inspite of this decrease in total daylit area.
• Clouds derived from extended satellite lidar/radar records have
proven fundamental for diagnosing significant changes to theplanetary radiative budget. EarthCARE is critical to continuing
the polar cloud record for extended climate study.
• Our goal is to replace climatological cloud with a twenty-year
CALIOP/EarthCARE cloud record by the middle of this decade.

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