Trends in Mid-Latitude Cyclone Frequency And Their Effect On Air Quality

Eric M. Leibensperger, Loretta J. Mickley, and Daniel J. JacobSchool of Engineering and Applied Sciences - Harvard University

GCAP Meeting – October 12, 2007

1999-2001 2049-2051

A Decrease in Mid-Latitude Cyclones: 2000-2050

1999-2001 vs. 2049-2051: 17% decrease

1999-2005 vs. 2049-2055: 16% decrease

[Wu et al., in press]

Past and Future Trends of Mid-Latitude Cyclones

[Lambert, et al., 2006]

Previous studies have found a decrease in the frequency of observed cyclones and cyclones objectively tracked from reanalysis data.

Additional studies have identified a decrease in cyclones in future climate simulations.

[McCabe, et al., 2001]

Mid-latitudes

High-latitudes

Storm Tracking

[Zishka and Smith, 1981]

720 km

990 mb

1000 mb

4x daily SLP fields (NCEP/NCAR or ECMWF Reanalysis, GISS GCM 3 4x5 and 2x2.5) used with the GISS Storm Tracker [Bauer and Del Genio, 2007]

1950-2005 Summer Cyclone Frequencies

NCEP/NCAR Reanalysis

GISS GCM 3– 2x2.5 – Specified SST

(data courtesy of Jean Lerner)

GISS GCM 3– 4x5 – Q-Flux Ocean

[Leibensperger et al., in prep.]

1980-2005 trend is comparable between GISS GCM 4x5 and Reanalysis

Relationship between Ozone and Mid-latitude Cyclones – 1980-1998

[Leibensperger et al., in prep.]

Correlation coefficient between # of cyclones and # of O3 exceedances

The frequency of cyclones tracking through the southern track is strongly anti-correlated with the number of ozone exceedances

Cyclone Frequency and Ozone in the Northeast

[Leibensperger et al., in prep.]

r=-0.29

r=-0.64Removing linear trends in cyclone frequency and exceedances enhances the anti-correlation

The Air Quality Penalty Due to Decreasing Cyclone Frequency

cyclonesemissions dtsexceedanced

dtsexceedanced

dtsexceedanced

)()()(

19 – 5 = 14 days

84.1)(

05.1)(

79.0)19.0)(15.4()()()()(

emissions

cyclones

dtsexceedanced

dtexeedancesd

dtcyclonesd

cyclonesdsexceedanced

dtsexceedanced days yr-1

days yr-1

days yr-1

[Leibensperger et al., in prep.]

Without the decrease in the number of cyclones, the number of exceedances would have been lowered to 5 rather than 19 days.

Future decreases in cyclone frequency will make air quality goals more difficult to achieve.

Future Work

CPD of CO tracer at the surface during low cyclone years versus high cyclone years is similar to Loretta’s findings for 2050

[Mickley et al., 2004]

COt = Carbon Monoxide Tracer

• Extend analysis from 1998 to 2006, publish results

• Use tracer within GCM to diagnose changes in transport

• Effects of climate change on air pollution meteorology

- Transport (cyclones, convection)

- Lightning

EXTRA SLIDES

Midwest at surface

Northeast at surface Southeast at surface

Midwest at 400hPa

Northeast at 400hPa Southeast at 400hPa

Less tracer makes it this high

Less outflow from N.A. – but more to the north, could be from increased frequency there

Most tracer sourced where lower track most effective – net effect is less in upper trop.

Time Series of Cyclones – NCEP/NCAR Reanalysis 1

Tropical Storm Brenda Hurricane Cleo

Time Series of Cyclones – GISS GCM 4x5

Time Series of Cyclones – GISS GCM 2x2.5

1. Can the GCM and reanalysis data reproduce expected cyclone statistics?

GISS 4x5 and NCEP main storm tracks are comparable to the observed main track frequencies in position. NCEP storm tracks well represented quantitatively, but GISS 4x5 is too low.

[Whittaker and Horn, 1984]

204060

(cyclones/20 years)

Cyclones in the GISS GCM III at 2ºx2.5º

The frequency of cyclones in the GISS GCM 2x2.5 is improved, but the tracks appear shifted to the southeast.

[Whittaker and Horn, 1984]

204060

(cyclones/20 years)

Main Summer Storm Tracks in the Models

Why mid-latitude cyclones?

In the northeastern United States, many variables affecting ozone production (temperature, cloud cover, stagnation) and transport change on a synoptic timescale thus making mid-latitude cyclones a major driver of surface ozone concentrations

Cold Warm

Lighter winds

Mean 4-10 Day Integrated Power of FFT of Max 8-hr Avg Time Series