1. The Role of Downward Infrared Radiation in the Recent Arctic Winter Warming Trend
Steven Feldstein1, Tingting Gong2, Sukyoung Lee1
1Department of Meteorology and Atmospheric Science,
Pennsylvania State University, University Park, PA
2Institute of Oceanography, Chinese Academy of Sciences,
Qingdao, China
21st Conference on Atmospheric and Oceanic Fluid Dynamics, Portland, Oregon, June 26-30, 2017

2. Question: What process accounts for the inter-decadal Arctic Amplification trend?
Data: European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) data

3. ΔC = ΔId + ΔIu + ΔFsh + ΔC Surface Energy Budget Analysis
Trend (Δ) of the Surface Energy Budget terms (Lesins et al. 2012)
ΔC = ΔId + ΔIu + ΔFsh ΔC
Downward IR
Storage
(very small)
Upward IR
surface
turbulence
heat fluxes
conduction
through ice
Expressing the upward infrared radiation (IR) as -εσTs4, the energy balance equation can be written as
ΔTs = (ΔId + ΔFsh + ΔC - ΔG)/(4εσTs3)
Neglect ΔC and ΔG. Ts and SAT are highly correlated (r=0.97;
Chen et al. 2003) over most of the Arctic.

4. Trend Calculation Δf = (δf/δxi)∆xi; f = SAT; ∆ = trend;
(δf/δxi) =rσ(SAT)/σ(xi) = regression coefficient
x1 = downward IR
x2 = surface heat flux
x3 = horizontal temperature advection;
x4 = adiabatic warming/cooling
For each winter, DJF mean values of f and xi for are subtracted in the regression coefficient calculation
Regression coefficient expresses the intraseasonal relationship between f and xi
Reference ENSO, our SOM papers, and Tim Palmer’s papers

5. Surface Energy Budget
SAT trend
SAT (Downward IR)
SAT (surf heat flux)
SAT (horiz temp adv)
SAT (adiabatic warm/cool)
Cooling
Period
Mention surface heat flux warming (from above) large over Greenland Barents and Kara Seas. Results suggest that ice albedo feedback small.
Warming
Period
SAT trend driven primarily by trend in downward IR, not by the surface heat flux trend

6. Energy Budget (regression coefficients and trends)
Downward IR
Surface Heat
Flux
Horizontal Temp
Advection
Adiabatic
Warming/Cooling
Regression
Coefficients
Trends

7. What processes drives the downward IR trend?
Downward IR trend index obtained by projecting daily
downward IR (poleward of 70N) onto downward IR trend pattern
Discuss increase in frequency of IR index.
IR(x,t) = IRindex(t)IRtrend(x) + residual
IRindex(t) = (∑i,jIR(x,t) IRtrend(x) cos θ)/(∑i,j IRtrend(x)2cos θ)
e-folding time scale = 10 days

8. What processes drives the downward IR trend?
Obtained from regression against the IR index
Moisture flux
& conv
Total column water
Downward IR
εsT4
εsT4 (adv)
Cooling
Period
Warming
Period
Downward IR trend is driven largely by a trend in the intrusions of
warm moist air into the Arctic

9. Moisture flux (convergence) & 250-hPa streamfunction (1991-2010 trends)
LVq
Total moisture flux trend
LV’TqC
Moisture flux trend due to circulation trend
LVCq’T
Moisture flux trend due to specific specific humidity trend
L(V’q’)T
Moisture flux trend due to transients
Moisture transport from midlatitudes
250-hPa Streamfunction

10. Daily Evolution
Lagged pattern correlations between regressed fields and trend patterns
Upward IR
SAT
Downward IR
Mention time sequence of processes and time scale
Moisture flux convergence
Total Column Water
Surface heat flux

11. Daily evolution (lagged regressions)
Downward IR
Upward IR
Net IR
Heat flux
Surface air temperature
Downward heat flux
Note that at positive lags upward IR > downward IR and surf heat flux changes from downward to upward. Consistent with sea ice melting.
Upward heat flux

12. 250-hPa wave activity fluxes & streamfunction: Wave activity transits the Arctic
Lag - 4
Lag - 2
Lag 0
Lag + 2
Lag + 4
Lag + 6
Lag + 8
Lag + 10

13. CONCLUSIONS
Arctic Amplification: Most of the inter-decadal Arctic surface warming trend arises from a trend in downward IR, not a trend in the surface heat flux (ice albedo feedback). The downward IR increase is due to moisture flux intrusions associated with poleward propagating Rossby waves, which bring warm moist air in the Arctic.
Moisture intrusions appear to be increasing in their frequency and amplitude.
Ice-albedo feedback during the previous summer does not appear to account for Arctic Amplification.