\documentstyle[12pt,agums]{article} 
%\documentstyle[jgrga]{article}
\lefthead{NEWMAN ET AL.}
\righthead{Preface}
\received{June, 1999}
\accepted{MMM DD, 1999}
\paperid{}
\cpright{}{}
\ccc{}

\authoraddr{P. A. Newman, Code 916, NASA GSFC,
Greenbelt, MD, 20771  (e-mail: newman@notus.gsfc.nasa.gov); 
D. W. Fahey, NOAA Aeronomy Lab, Boulder, CO(fahey@al.nasa.gov); 
W. H. Brune, Pennsylvania St. Univ., University Park, PA, 16802 (brune@ems.psu.edu); 
M. J. Kurylo, Code YS, NASA HQ, Washington D. C., 20546-0001 (mkurylo@hq.nasa.gov);
S. R. Kawa, Code 916, NASA GSFC, Greenbelt, MD, 20771  (e-mail: kawa@maia.gsfc.nasa.gov)}

\setcounter{secnumdepth}{0} \begin{document} \title{Preface}

\author{Paul A. Newman} 
\affil{NASA Goddard Space Flight Center, Greenbelt, MD} 

\author{David W. Fahey} 
\affil{NOAA Aeronomy Lab, Boulder, CO} 

\author{William H. Brune} 
\affil{Pennsylvania State University, University Park, PA} 

\author{Michael J. Kurylo} 
\affil{National Institute of Standards and Technology, Gaithersburg, MD and NASA Headquarters, Washington, D. C.} 

\author{S. Randolph Kawa} 
\affil{NASA Goddard Space Flight Center, Greenbelt, MD} 

\begin{abstract} 

The Photochemistry of Ozone Loss in the Arctic Region In Summer
(POLARIS) mission was designed to investigate the natural summer
decrease of stratospheric ozone levels.  Both polar regions have large
and distinct annual cycles of ozone column amounts.  In northern
spring, the average level is over 450 Dobson units (DU), decreasing to
less than 275 DU by September.  In order to cover this period of ozone
decrease, POLARIS was conducted in three deployment phases from
Fairbanks, Alaska, (65\deg N) during the summer of 1997.  The principal
measurement platforms were the NASA ER-2 high-altitude aircraft and
stratospheric balloons.  Additional measurements were provided by
ground-based instruments, sondes, and satellites.  POLARIS observations
included ozone, meteorological variables, particles, long-lived
chemicals, and short-lived radicals.  During the field deployments,
several modeling and theoretical groups participated in flight planning
and data evaluation activities.  The interpretive studies in this
Special Section of the Journal of Geophysical Research are a first
comprehensive examination of the POLARIS data set, addressing
stratospheric ozone abundances and its changes; the role of aerosols;
details of the photochemistry of reactive species; transport of
stratospheric air and the correlations of long-lived species; and
measurement intercomparisons.

\end{abstract}

\begin{article}

\section{Introduction}

Ozone both screens the Earth from the biologically harmful effects of
solar ultraviolet radiation and is a radiatively active gas in both the
UV and the IR portions of the solar spectrum.  Changes in global ozone
amounts will impact both greenhouse warming severity and the Earth's
biota \cite{wmo}.  Hence, a precise understanding is needed of how
changes in atmospheric composition (e.g., aircraft emissions or
anthropogenic trace gas releases) might cause ozone changes.  This
requires a thorough understanding the chemistry and transport processes
that control ozone in the stratosphere.

The polar stratospheres are unique regions for ozone because of the
cold continuous darkness in winter and the warm continuous daylight in
summer.  In winter, stratospheric temperatures are quite low (see e.g.,
{\it Coy et al.} [1997a]), enabling a variety of chemical
reactions to occur on polar stratospheric cloud particles \cite{peter,
poole}.  The continuous daylight in polar summer enables a much
different chemical environment than is observed at similar times in
mid-latitudes or the tropics \cite{farman, johnston, faheyravi}.  The
summer polar temperatures in the lower stratosphere are quite warm and
the mean circulation is in an easterly flow (e.g., see {\it Wu et al.,}
[1984]).  In addition, eddy flux quantities (such as the heat flux)
show that the transport is considerably weakened (again, see {\it Wu et
al.,} [1984]).  Weakened dynamics results in a much reduced transport
of ozone from the tropical photochemical production region into the
Arctic lower stratosphere \cite{wu,gettelman}.  However, significant
wave effects have been observed in ozone and other trace gases, where
low ozone was correlated with high NO \cite{park}, implying important
roles for both photochemical and transport effects.

Ozone abundances show a distinct seasonal cycle in areas away from the
tropical ozone production region.  At northern high latitudes, ozone
column amounts peak in spring and reach minimum values in late
summer/early fall \cite{dobson,london,krueger,bojkov} (see
\callout{Figure~\ref{fig:zm_tot_o3}}).  This spring-to-fall Arctic
decrease was first recognized following the pioneering
spectrophotometer measurements of Dobson and his colleagues
\cite{dobson}.  The decrease is attributed to an increased role of
NO$_{x}$ catalytic cycles in ozone destruction during periods of
prolonged solar illumination at summer polar latitudes \cite{johnston}
and reduced poleward transport of ozone.  Increased NO$_{x}$ also
moderates the effectiveness of the Cl$_{x}$ (= Cl + ClO) and HO$_{x}$
(= OH + HO$_{2}$) ozone loss cycles \cite{bruhl}.  However, model
simulations of this decrease have generally overestimated ozone in the
polar region \cite{chipperfield}.  The winter-to-spring build-up of
ozone was originally ascribed to a mean poleward and downward transport
effect by {\it Brewer} [1949] and {\it Dobson} [1956], and later
refined with the development of the ''transformed Eulerian mean''
circulation \cite{edmon, dunkerton}.  While conventional meteorological
data have been used to validate the winter build-up of ozone at high
latitudes, less progress has been made in validating the photochemical
loss of ozone over the course of the summer.

The POLARIS mission was designed to understand the photochemical and
transport processes that cause the summer polar decreases in
stratospheric ozone.  The mission primarily utilized the NASA ER-2
high-altitude aircraft and balloon platforms while based in Fairbanks,
Alaska.  Additional data were obtained with ground-based instruments,
satellites, and sondes.  Measurements  included meteorological
variables; long-lived tracers for assessing summertime transport
questions; reactive species within the reactive nitrogen (NO$_{y}$),
halogen (Cl$_{y}$), and hydrogen (HO$_{x}$) reservoirs; and aerosols.
These stratospheric measurements were made at mid- to high latitudes in
spring and summer.  These observations have been combined with various
computer models of the atmosphere to evaluate summer ozone changes due
to chemistry and transport.

Following this introduction to the POLARIS mission are sections that
acknowledge the programmatic background of the mission, describe the
mission logistics, provide highlights of the separate deployment
phases, describe the science topics included in the papers accompanying
this Special Section, and summarize the overall mission .

\section{Program background}

POLARIS was sponsored by the National Aeronautics and Space
Administration through its Upper Atmosphere Research Program (UARP),
Atmospheric Effects of Aviation Project (AEAP), and Atmospheric
Chemistry Modeling and Analysis Program (ACMAP) in cooperation with the
National Oceanic and Atmospheric Administration (NOAA) and the National
Science Foundation (NSF).

%The principal sponsors for POLARIS were the National Aeronautics and
%Space Administration (NASA), the Aeronomy Laboratory of the National
%Oceanic and Atmospheric Administration (NOAA), and the National Center
%for Atmospheric Research (NCAR) of the National Science Foundation
%(NSF).  NOAA and NSF provided partial funding for some mission
%participants and other costs.  

NASA's support follows from its Congressional mandate ``to provide for
an understanding of and to maintain the chemical and physical integrity
of the Earth's upper atmosphere.''  NASA has developed and continues to
implement a long-range scientific research program aimed at providing a
comprehensive understanding of atmospheric processes occurring
throughout the upper troposphere and stratosphere.  As the experimental
component of this NASA program, UARP focuses on process-study
investigations with the specific objective of understanding the
chemical, physical, and transport processes within these regions and
their control on the distribution of atmospheric species such as
ozone.  Such understanding enables the prediction of possible
perturbations to atmospheric composition caused by human activities and
natural phenomena.  AEAP is further mandated to develop a scientific
basis for the assessment of the effects of aviation on ozone and
climate.

UARP-sponsored research falls into three categories: field
measurements, laboratory studies, and process study modeling and data
analysis.  Campaigns such as POLARIS constitute a major component of
UARP field measurements.  In the past two decades, significant
measurement results have been derived from campaigns such as the
Stratosphere Troposphere Exchange Project (STEP); the Airborne
Antarctic Ozone Experiment (AAOE); the first and second Airborne Arctic
Stratospheric Expeditions (AASE I and II); the Stratospheric
Photochemistry, Aerosols, and Dynamics Expedition (SPADE); the Airborne
Southern Hemisphere Ozone Experiment / Measurements for Assessing the
Effects of Stratospheric Aircraft (ASHOE-MAESA); the Stratospheric
Tracers of Atmospheric Transport airborne experiment (STRAT) and
concurrent balloon campaigns such as the Observations from the Middle
Stratosphere (OMS) campaigns.  Since many of the AEAP scientific
objectives are encompassed by the broader goals of UARP, a strong
UARP/AEAP field measurement partnership was fostered for ASHOE-MAESA,
STRAT, and OMS and continued for POLARIS.

NASA's UARP, NASA'S AEAP, and Japan's NASDA provided support for two
balloon flights from Fairbanks carrying a variety of instruments during
the April-May POLARIS phase.  The flights, which were designed to
provide correlative observations for the Japanese Advanced Earth
Observing Satellite (ADEOS), also provided data of value for POLARIS.

\section{Mission description}

The principal measurement platforms for POLARIS were the NASA ER-2
aircraft and balloons.  The four balloon flights included the two
supporting the ADEOS satellite correlative measurements,  one of the
NASA OMS in-situ payload, and one flight of the OMS remote payload.
Small balloons also were used for ozone sondes throughout the mission.

\subsection{Spatial and temporal coverage}

The 35 ER-2 and 4 balloon flights during the POLARIS campaign covered
the entire summer period and latitudes from the equator to the pole
(see \callout{Table~\ref{table:tbl-1}}).  Figure~\ref{fig:zm_tot_o3}
displays the flight tracks of the NASA ER-2 (black lines) superimposed
on an image of the total ozone concentrations from the Earth Probe
Total Ozone Mapping Spectrometer (TOMS) instrument.  The three
deployment phases of POLARIS are seen as the groupings of the black
lines in Figure~\ref{fig:zm_tot_o3} and are also noted in
Table~\ref{table:tbl-1}.  The phases occurred in April-May (Phase I),
June-July (Phase II), and September (Phase III).  Most of the flights
were flown from Fairbanks, Alaska (65\deg N), with a few flown from the
NASA Ames Research Center (ARC) (37\deg N), and one flight flown to
3\deg S from Barbers Point, HI (21\deg N).  The region of continuous
(24-hour per day) sunlight is indicated by the white line in
Figure~\ref{fig:zm_tot_o3}.  Deployment Phase I occurred after
continuous daylight began at the north pole, Phase II was timed to the
summer solstice when continuous daylight was covering the maximal
amount of the polar area, and Phase III was timed to cover the
disappearance of continuous polar daylight at summer equinox.

The altitudes sampled during POLARIS extended from the surface to
approximately 20 km for the ER-2, and up to 30 km for the ADEOS and OMS
balloon flights.  \callout{Figure~\ref{fig:vert_fair_o3}} displays the
altitude profiles of the ER-2 and balloon flights (white thin lines).
These altitude profiles are superimposed on ozone partial pressure
contours as derived from the separate ozone sonde launched from
Fairbanks.  The three phases of POLARIS are seen again in the groupings
of the lines over the course of the summer period.  The ADEOS and OMS
balloon flights are labeled on the figure, and are also differentiated
from the ER-2 flights by the greater maximum altitudes.

The POLARIS flights covered latitudes from  3\deg S to 90\deg N (see
Table~\ref{table:tbl-1}).  \callout{Figure~\ref{fig:horiz_o3}} shows
the three POLARIS deployment sites, the latitude/longitude extent of
all mission flights, and the May-September 1997 average of TOMS total
ozone.  ADEOS and OMS balloon flights were all launched from Fairbanks
and generally landed near to Fairbanks depending on wind speeds.  The
ozone sondes were launched at the University of Alaska in Fairbanks
throughout the April to September period and with higher frequency
during the deployment phases \cite{lloyd}.  The launch dates are
indicated by the dark triangles at the bottom of Figure
\ref{fig:vert_fair_o3}.  These sondes provided near-continuous
monitoring of overhead ozone amounts over the course of the three
POLARIS deployments.

During the mid-summer period, the polar region is surrounded by a
maximum of ozone near 60\deg N as is apparent in
Figure~\ref{fig:horiz_o3} (see e.g., {\it Godson,} [1960]).  Fairbanks
is located poleward of this maximum in the region where ozone decreases
by a large amount between spring and fall.  Hence, POLARIS was staged
from Fairbanks because of the proximity to the region of continuous
sunlight and the region of large spring to fall ozone change.

The evolving meteorological fields influenced the planning of ER-2
flight paths and launch opportunities for the balloons.  Because
clearance into Russian controlled airspace was difficult to obtain,
flights were also restricted to the western hemisphere.  An important
parameter choosing air masses to be sampled on ER-2 flights was the
extent of solar exposure received by an air mass in the preceding five
to ten days.  This and other flight planning tools were utilized to
sample a gradient in solar exposure and reach maximum possible values.

\subsection{Airborne payloads}

The list of POLARIS ER-2 Principal Investigators, the measured
parameters, and the measurement technique are listed in
\callout{Table~\ref{table:tbl-2}}.  This payload provides measurements
of radical, reservoir, and source gases in all of the major
stratospheric families (chlorine, bromine, nitrogen, oxygen, and
hydrogen).  In addition, measurements of the UV and visible solar
spectrum, particle number and size, and meteorological variables
provided necessary data for fully detailing the dynamics and chemistry
of the lower stratosphere.  The POLARIS ER-2 payload was expanded over
that of previous missions with the addition of both in situ and remote
measurements.   New in situ measurements included ClONO$_{2}$ and an
additional measurement of NO$_{2}$ (Harvard Univ.) The ClONO$_{2}$
measurements are the first to be made in situ in the stratosphere
\cite{stimpfle}.  New remote measurements include those of the
submillimeter limb sounder (SLS).  With the exception of the SLS
instrument, the payload in Table~\ref{table:tbl-2} was flown on all
POLARIS flights.  SLS and a small subset of the full payload were flown
on the ER-2 transit flights between Moffett Field, CA, and Fairbanks
between the Phase I and II, and Phase II and III deployments.

The POLARIS OMS activities made use of a remote sensing payload and an
in-situ measurements payload (see \callout{Table~\ref{table:tbl-3}}).
The in-situ payload focused on measurements of long-lived trace gases
for investigating stratospheric transport issues.  The remote payload
combined an in situ ozone measurement with the long-path absorption
measurements of the MkIV Fourier transform interferometer (FTIR) (see
Table~\ref{table:tbl-3}).  The MkIV FTIR measured a wide range of
radicals, reservoir species, and long-lived trace gases.

The ADEOS correlative balloon flights included two payload
configurations, both including remote and in situ instruments (see
\callout{Table~\ref{table:tbl-4}}).  The payloads were flown on 30
April 1997 and 8 May 1997.

\subsection{Ground-based observations}

Ground-based instruments of ozone column amounts were provided by two
spectrophotometers at Fairbanks (Table~\ref{table:tbl-4}) during  and
between  the deployment phases in conjunction with the UV and visible
radiation measurements made on the ER-2 {\it Lloyd et al.} [1999].
Between deployment phases, the MkIV FTIR instrument was also used
on the ground at Fairbanks to measure many of the molecules listed in
Table~\ref{table:tbl-4}.

\subsection{Satellite investigations}

Satellite and ground station measurements of ozone form the backbone of
the global ozone monitoring system.  These ozone data are essential
information for global monitoring of stratospheric ozone change
\cite{wmo}.  Linking the POLARIS observations to satellite and
ground-based measurements was important ito establishing an overall
understanding of the evolution of polar ozone from spring to fall.  The
Earth Probe TOMS, ADEOS TOMS, the Upper Atmosphere Research Satellite
(UARS) Halogen Occultation Experiment (HALOE), the UARS Microwave Limb
Sounder (MLS), and Stratospheric Aerosol and Gas Experiment (SAGE II)
instruments all provided ozone measurements that contributed to POLARIS
field and analysis activities (see Table~\ref{table:tbl-4}).  In
addition, HALOE and SAGE II measured other species that were also
measured by the ER-2 and balloon instrument payloads.  For example,
NO$_{2}$ was measured by SAGE II, HALOE, the MkIV FTIR, and two
instruments aboard the ER-2 (see Tables 2, 3, and 4).

\subsection{Theoretical investigations}

Accurate meteorological forecasts and theoretical modeling of the
stratosphere were important aspects of the POLARIS mission.
Meteorological forecasts by the GEOS-1 model of the NASA/GSFC Data
Assimilation Office were used in the detailed flight planning of the
ER-2 \cite{coy97a, coy97b}. Analyses derived from this same
assimilation system were used to compute air mass trajectories
\cite{schoeberl}, and to detail the evolution of the stratospheric
meteorological conditions over the course of the summer.  In
addition, satellite cloud images and forecast data were used to
forecast the movement of cirrus cloud systems.  All of this information
was transferred, exchanged , and integrated on field workstation
computers used for flight planning.

Models of the chemical and photolysis fields provided a basis for
comparison to observations.  These model predictions and post-flight
comparisons to data revealed key agreements and discrepancies that have
been subsequently utilized to confirm and  refine our understanding of
the stratosphere.  The Principal Investigators for modeling and
forecasting activities are detailed in
\callout{Table~\ref{table:tbl-5}}.

Forecasting air motions in the winter stratosphere is principally
done using potential vorticity and temperatures \cite{tuck}.  During
summer, the weak easterly circulation, lack of a well defined vortex,
and lack of a distinctive cold air region makes accurate
forecasting quite difficult.  Because the chemistry is dependent on the
continuous sunlight, new forecast products were developed to find air
masses that had undergone continuous sunlight for extended periods.
These ``solar exposure fields'' utilized GEOS-1 model forecast
information to calculate the time that air parcels had been exposed to
sunlight with solar zenith angles less than 92\deg.  The fields
are calculated using a 1\deg latitude by 1\deg longitude grid of points
with an isentropic trajectory model \cite{newman,schoeberlx} that
integrates the amount of sunlight encountered by an air mass over a 10
day period.  As an example, the flight of 13 May is superimposed on
the solar exposure field in \callout{Figure~\ref{fig:solx}}.  The
flight was planned to cross an air mass which was moving southward from
the pole to North America.  This air had received  nearly
continuous exposure for 10 days.  The flight track bearing was
slightly east of north to further encounter an air mass that
recently come northward from the eastern hemisphere.  All of the
POLARIS ``photolysis'' flights (see Table~\ref{table:tbl-1}) were
planned using these solar exposure fields.  Such products and the
conventional meteorological products were the tools used for planning
the POLARIS flights.

\subsection{Deployment Descriptions}

\subsubsection{Phase I: April-May}

This ER-2 flight series covered a latitude range from 13\deg N to
90\deg N at cruise altitudes near 20 km in the lower stratosphere.  On
most flights, vertical coverage extended from approximately 15 to 21 km
at selected latitudes.  Several full vertical profiles were obtained
between cruise altitude and the surface at the two deployment sites,
ARC (37\deg N) and Fairbanks (65\deg N).

A number of POLARIS objectives were achieved in this phase.  First, the
ER-2 penetrated the northern polar vortex on 26 April 1997 during a
flight that reached the north pole.  In the spring of 1997, the polar
vortex had unusually low ozone and persisted for an exceptionally long
period (see {\it Geophysical Research Letters, 24} [1997] for a series
of articles describing these low ozone values).  Second, the ER-2
completed flights that separately included a sunrise (30 April 1997)
and sunset (9 May 1997) at high latitudes in the stratosphere.  The
data indicated unusual asymmetries in the behavior of hydrogen radicals
at low-angle solar illumination.  Third, the ER-2 sampled stratospheric
air masses that had experienced continuous sunlight for periods ranging
from 1 to 12 days (2, 6, and 13 May 1997).  These flights revealed
important observational-model (photochemical steady-state and
trajectory) discrepancies with respect to NO$_{x}$ concentrations.
Fourth, there were two successful launches of the ADEOS balloon
payloads.

\subsubsection{Phase II: June-July}

With the ER-2 based solely in Fairbanks during Phase II, the latitude
survey range extended from 47.7\deg N to 90\deg N in the lower
stratosphere.  Vertical coverage to 21 km in the Fairbanks region was
quite good because of dedicated  flights on 30 June 1997 and 10 July
1997 that included a number of flight legs at specific altitudes in the
upper troposphere and lower stratosphere.  In addition, vertical
profiles were obtained over the 15- to 20-km altitude range near
47.7\deg N and 90\deg N.

POLARIS objectives were achieved in this phase included sampling of
mid-summer polar air that had undergone continuous solar exposure for
an extended period;  OMS balloon flights using the in situ and MkIV
FTIR payloads to altitudes in excess of 30 km (performed coincidentally
with ER-2 flights); and sampling of winter polar vortex fragments in
mid-summer.

\subsubsection{Phase III: September}

Phase III ER-2 flights included latitudes extending from 90\deg N to
3\deg S in the lower stratosphere.  Both sunrise and sunset flights in
late summer were conducted over the Fairbanks region, similar to those
flown in Phase I.  In addition, a midday solar zenith angle flight was
flown, providing a nearly full scan of solar zenith angles from sunrise
to sunset in similar air masses.

As the final component of this phase, the ER-2 transited to Barbers
Point, Hawaii, performed a flight to slightly south of the equator, and
returned to ARC.  Vertical profiles from the ground to 21 km occurred
at Fairbanks, Hawaii, and ARC, with profiles over the 15- to 20-km
altitude range near 3\deg S and 90\deg N.

\section{POLARIS Science topics}

This collection Journal of Geophysical Research papers is the first to
interpret the POLARIS data set in a comprehensive manner.  These papers
address stratospheric ozone abundances and its changes; the
photochemical role of aerosols; details of the photochemistry of
reactive species; transport of stratospheric air and the correlations
of long-lived species; and measurement intercomparisons.  Data from
ground-based instruments and those on the ER-2 aircraft, balloons,
satellites, and sondes are included, thereby representing the full
range of available observational data.  In addition, many papers rely
directly or indirectly on meteorological analyses.  Box models,
trajectory models, and 2-D and 3-D photochemical transport models are
widely used to add value to the observations.  Finally, these papers
are augmented by several that have or will be published separately
since the end of the POLARIS field campaign
\cite{gao,osterman,wennberg,hurst,hintsa,nevison}.

The most extensive observations available for POLARIS are those of
ozone in column and profile abundances.  Each data set clearly marks
the late spring-to-summer decline in ozone amounts.  Intercomparisons
show good systematic agreement among the various data sets
\cite{lloyd,toona,toonb}.

The ozone observations form the basis for addressing an important
objective of POLARIS: Are the observed summer ozone decreases
consistent with our understanding of transport and chemical processes?
With the papers included here, a fully consistent picture has yet to
emerge \cite{pierce,rosenlof,toona,hitchman}.  However, the combination
of models and observations confirm the role of photochemistry in summer
ozone decreases at high latitudes.  In general, ozone amounts
throughout the stratosphere represent a balance of transport and
photochemical production and destruction processes.  The photochemical
contribution was calculated directly or deduced as a difference between
net ozone changes and the transport contribution.  Similarly, transport
contributions can be calculated directly from the residual circulation
which usually brings air to high latitudes from lower latitudes or
deduced as a difference using calculated photochemical changes.  In
addition, column ozone amounts change as a result of synoptic waves
disturbing the tropopause region \cite{hitchman}.

The large number of long-lived and radical species measured during
POLARIS provide an unprecedented opportunity to diagnose photochemical
processes and measure trace species abundances in the summer high
latitude stratosphere
\cite{delnegro,jucks,randeniya,sen,stimpfle,swartz,gao,osterman,wennberg,
hurst,hintsa,drdla}.  A highlight of the results are the analyses of the
partitioning of the NO$_{y}$ and Cl$_{y}$ reservoirs.  The enhanced and
uninterrupted solar illumination at summer high latitudes increases the
abundance of NO$_{x}$ within the NO$_{y}$ reservoir and the associated
catalytic ozone loss.  Comparisons using box models constrained by
observations and other models showed unsatisfactory agreement when
using currently recommended kinetic rate coefficients.  More recent
measurements of the rates of the gas-phase reactions of OH with
NO$_{2}$ and HNO$_{3}$ by {\it Brown et al.,} [1999] and {\it
Dransfield et al.,} [1999] have substantially improved the agreement in
most comparisons.  The sunrise and sunset flights revealed the need for
an additional HOx source in current models.  The source could be the
long-wavelength (>650 nm) photolysis of HNO4.  The NO$_{y}$ analyses
benefited from two in situ measurements of NO$_{2}$ on board the ER-2
aircraft which showed good agreement throughout the mission and were
consistent with the NO observations.  The evaluations of the
partitioning within the Cl$_{y}$ reservoir demonstrate a good
understanding throughout the lower stratosphere.  New in situ
measurements of ClONO$_{2}$ on the ER-2 aircraft were an important
addition to these analyses.  An analysis of the hydrogen budget also
shows good agreement in the lower stratosphere.

Aerosols play a lesser role in the chemistry of the summer stratosphere
because N$_{2}$O$_{5}$ formation becomes negligible in regions of
continuous solar illumination \cite{farman,gao,osterman}.  However, the
summer stratosphere provides a unique opportunity to evaluate aerosol
processes at warm temperatures ($>$ 210K).  The results suggest no new
significant role of aerosol processes in the summer but highlight the
need for more further study of several potentially important reactions
\cite{drdla}.  Measurements of soot particles on the ER-2 aircraft
significantly enhanced available observations in the lower stratosphere
\cite{strawa}.  The results suggest that reactions on soot particles
likely do not have a significant role in controlling the partitioning
with the NO$_{y}$ reservoir in agreement with previous studies.

Special features of the POLARIS mission are the sampling of air from
tropical latitudes in late spring and late summer and from the Arctic
vortex in late April.  These new data from aircraft and balloons extend
data sets acquired in previous missions and with other platforms.  The
papers here use these new data sets in part to address transport of air
into the tropics and within high latitudes
\cite{andrews,flocke,ray,rex,romashkin}.  Tropical and mid-latitude
measurements of species with a wide range of lifetimes were used to
quantify the rate of transport of air from mid latitudes to the inner
tropics.  The results indicated more rapid transport into the tropics
than found in earlier studies.  Measurements of CO$_{2}$ were used to
evaluate the vertical age distribution in the tropical lower
stratosphere.  SF$_{6}$ and CFC observations were used in a unique
analysis to estimate the fraction of air in the lowermost stratosphere
at midlatitudes which is from the tropical troposphere and from the
stratospheric overworld.  With long-lived tracer correlations of
CH$_{4}$, NO$_{y}$, and N$_{2}$O, mixing processes associated with the
Arctic polar vortex were clarified with a specific emphasis on
validating the occurrences of denitrification.  Correlations and
age-of-air information were also used to clarify how stratospheric
abundances of methyl chloroform are changing in response to changes in
tropospheric emission rates.

\section{Summary}

The POLARIS mission was conducted over the course of the 1997 summer.
The POLARIS ER-2 aircraft and OMS balloon flights provide an
unprecedented glimpse of polar summer chemistry, dynamics, and
radiation.  The logistic success of POLARIS is demonstrated by the 35
ER-2 and 4 balloon flights completed over the late spring and summer
period and by the large body of data that has been archived from the
wide variety of airborne, satellite, and balloon data and model
results.

The natural decrease of ozone over the course of the summer has been
well documented by decades of ground and satellite observations.  The
chemistry and dynamics of the summer period have only been partially
understood from a theoretical basis, and limited satellite
observations.  The new POLARIS observations have firmly grounded our
theoretical expectations with a large body of new observational
evidence.

The papers included in this Special Section attest to the scientific
success of POLARIS.  The papers address key issues concerning the
photochemistry and transport in the stratosphere and provide important
new detail of the causes underlying changes in summer ozone amounts.

A highlight of the photochemical investigations is the detailed
comparison of radical and reservoir measurements with models.  These
results initially revealed important discrepancies and agreements in
our understanding of stratospheric chemistry.  These observations
encouraged new laboratory measurements, which have led to revised
reaction rate recommendations that significantly improve model
performance.  These model improvements provide greater confidence in
our predictions of future stratospheric change.

POLARIS and other NASA sponsored missions are described at the NASA
Ames Earth Science Division Project Office web site
(http://cloud1.arc.nasa.gov/).  The POLARIS data set and data sets from
all the mission prior to POLARIS are available on CD-ROM by request
from the NASA Ames Earth Science Division Project Office.

\end{article}

\begin{acknowledgments}

The POLARIS mission could not have been conducted without the
outstanding and committed work of the NASA ER-2 and National Science
Balloon Facility (NSBF) crews and personnel.  We are particularly
grateful to the ER-2 pilots who flew long missions out over the Arctic
in regions where air-sea rescue would have been nearly impossible.  The
POLARIS pilots were James Barrilleaux, Kenneth Broda, William Collette,
Jan Nystrom, and DeLewis Porter.  The near-flawless ER-2 performance
was due, in part, to the hard work of the ground crews and their crew
chiefs: James Barnes, Ronald Norris, and Myron Yorks II.  The balloon
launches were extremely difficult. We can testify to the
dedication and hard work of the NSBF personnel who made the balloon
flights a magnificent success:  the NSBF launch team, Danny Ball, Ed
Fritsch, Mark Cobble, and James DePue.

The POLARIS campaign was staged primarily at the Fort Wainwright United
States Army base in Fairbanks, Alaska.  The Army personnel were
gracious and accomodating hosts and were extraordinarily patient with
our large group of civilians. In particular, we extend our appreciation
to Emmett Holley (Commander), William Strauss (Chief of Operations),
and Ronald Kinman (Airfield Manager).  We also thank the personnel of
the Fairbanks National Weather Service Office.

The Airborne Project Office of the NASA Ames Research Center put
together an extraordinary effort to manage and prepare for POLARIS.  We
would like to specifically note the contributions of Stephen Hipskind,
Michael Craig, Steven Gaines, Joseph Goosby, Quincy Allison, Sue
Tolley, and John Chesterman.  They were assisted by Catherine Burgdorf
and Thomas Thompson of the NOAA Aeronomy Lab.  In particular, Michael
Craig's work as the Deputy POLARIS Project Manager and Instrument
Coordinator went well beyond the call of duty toward making POLARIS a
success.  Finally, we recognize Kathy Wolfe's tireless effort in
negotiating hotel accommodations for over 100 persons, coordinating
important mission activities in preparation for POLARIS and in the
field deployments, and in organizing the POLARIS Science Team meeting
in Snowmass, Colorado, in June 1998.


\end{acknowledgments}

\newpage

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\begin{figure} 
\caption{Values of total column ozone from the Total Ozone Mapping
Spectrometer (TOMS) instrument on the Earth Probe satellite shown as a
function of time and latitude during 1997.  Contour lines are labeled in Dobson
Units (DU, m-atm cm) and separated by 15 DU.  No observations are
available for the white open areas at high latitudes.  The dark
vertical lines represent ER-2 flight tracks during POLARIS.  The thick
white line denotes the boundary of continuous daylight.
\label{fig:zm_tot_o3}}
\end{figure}

\begin{figure} 
\caption{Values of ozone in milli-Pascal (mPa) as a function of time
and pressure altitude (pressure) during the April to September period
of 1997.  Contours are separated by 2 mPa.  Observations are from ozone
sondes launched from Fairbanks, Alaska, (65\deg N) on dates marked by
yellow triangles at the bottom of the figure.  The thin white vertical
lines represent the altitude range of ER-2 flights during POLARIS.  The
thin white lines extending to the top of the image represent the ADEOS
and OMS balloon flights.  The thick white horizontal line represents
the tropopause.
\label{fig:vert_fair_o3}}
\end{figure}

\begin{figure} 
\caption{TOMS total ozone averaged from May 1997 through September
1997. Fairbanks, AK, was the principal POLARIS basing site, with a series of
test flights from NASA/Ames, and a single flight to the equator flown
from Barber's Point, HI.  All of the POLARIS ER-2 flights are shown in
black.  
\label{fig:horiz_o3}} 
\end{figure}

\begin{figure} 
\caption{Solar exposure field for 13 May 1997.  The colors represent
the fraction of time spent by an air parcel in sunlight over the period
03-13 May (see scale on left).  The ER-2 flight of 13 May is
superimposed on this field as the thick black line.
\label{fig:solx}} 
\end{figure}

\newpage

\begin{planotable}{llrccll}
\tablewidth{41pc}
\tablecaption{POLARIS Flight Log}
\tablenum{1}
\tablehead{Date & Type & Flight  & POLARIS & Lat. & Comments \\
                &      & Hours   & Flight 
}

\startdata
\label{table:tbl-1}

\cutinhead{Phase I} \nl

970416 & ER-2 & 2.00 & 97-01 & 35\deg - 38\deg N & check flight \nl
970418 & ER-2 & 5.00 & 97-02 & 36\deg - 38\deg N & check flight \nl
970422 & ER-2 & 7.75 & 97-03 & 14\deg - 38\deg N & south survey from ARC \nl
970424 & ER-2 & 6.00 & 97-04 & 37\deg - 66\deg N & Transit ARC to FAI \nl
970426 & ER-2 & 8.00 & 97-05 & 65\deg - 90\deg N & N. Pole---Into vortex \nl
970430 & ER-2 & 6.50 & 97-06 & 64\deg - 65\deg N & Sunrise \nl
970430 & ADEOS & 8.77 & 429N & 65\deg N          & Correlative balloon \nl
970502 & ER-2 & 7.58 & 97-07 & 65\deg - 71\deg N & Photolysis---Canada \nl
970506 & ER-2 & 6.83 & 97-08 & 65\deg - 79\deg N & Photolysis---Canada \nl
970508 & ADEOS & 8.55 & 431N & 65\deg N          & Correlative balloon \nl
970509 & ER-2 & 6.17 & 97-09 & 64\deg - 65\deg N & Sunset \nl
970511 & ER-2 & 4.92 & 97-10 & 62\deg - 65\deg N & Stack \nl
970513 & ER-2 & 6.67 & 97-11 & 65\deg - 85\deg N & Photolysis---North \nl
970515 & ER-2 & 5.33 & 97-12 & 65\deg - 37\deg N & Transit FAI to ARC \nl \nl

\cutinhead{Phase II} \nl

970623 & ER-2 & 5.25 & 97-13 & 37\deg - 65\deg N & Transit ARC to FAI \nl
970626 & ER-2 & 7.75 & 97-14 & 55\deg - 77\deg N & Photolysis---North \nl
970629 & ER-2 & 6.75 & 97-15 & 48\deg - 65\deg N & Photolysis---South \nl
970630 & OMS  & 5.78 & 435N  &    65\deg N       & In situ balloon\nl
970630 & ER-2 & 4.58 & 97-16 & 63\deg - 67\deg N & OMS comparison \nl
970704 & ER-2 & 8.25 & 97-17 & 48\deg - 71\deg N & Photolysis---North/South \nl
970707 & ER-2 & 8.00 & 97-18 & 65\deg - 90\deg N & Photolysis---North \nl
970708 & OMS  & 6.93 & 436N  & 65\deg N          & MkIV balloon \nl
970710 & ER-2 & 5.50 & 97-19 & 64\deg - 65\deg N & Stack \nl
970712 & ER-2 & 5.50 & 97-20 & 65\deg - 37\deg N & Transit FAI to ARC \nl \nl

\cutinhead{Phase III} \nl

970902 & ER-2 & 5.50  & 97-21 & 37\deg - 65\deg N & Transit ARC to FAI \nl
970908 & ER-2 & 7.75  & 97-22 &  65\deg - 86\deg N & Photolysis \nl
970910 & ER-2 & 0.50  & 97-23 &  64\deg - 65\deg N & Abort after takeoff \nl
970911 & ER-2 & 4.25  & 97-24 & 64\deg - 65\deg N & Sunset flight \nl
970914 & ER-2 & 6.40  & 97-25 & 64\deg - 65\deg N & Sunrise \nl
970918 & ER-2 & 8.00  & 97-27 & 65\deg - 90\deg N & Photolysis---North Pole \nl
970919 & ER-2 & 7.30  & 97-28 & 64\deg - 65\deg N & East/West \nl
970921 & ER-2 & 7.33  & 97-29 & 65\deg - 21\deg N & Transit FAI to BP \nl
970923 & ER-2 & 8.00  & 97-30 & 21\deg N - 3\deg S & South survey \nl
970925 & ER-2 & 6.00  & 97-31 & 21\deg - 37\deg N & Transit BP to ARC \nl \nl

\end{planotable}

\begin{planotable}{lllll}
\tablewidth{41pc}
\tablecaption{POLARIS ER-2 Instrument Payload}
\tablenum{2}
\tablehead{PI & Institution & Instrument & Measurements & Technique }
\label{table:tbl-2}

\startdata

J. Anderson & Harvard & H$_2$O & H$_2$O & Lyman-$\alpha$ hygrometer \nl
E. Hintsa & & & & \nl
\nl

J. Anderson & Harvard & HO$_x$ & OH, HO$_2$ & Chemical titration and laser-induced \nl
P. Wennberg & &  &  & fluorescence \nl
\nl

J. Anderson, & Harvard and & ClONO$_2$ & ClONO$_2$, ClO & Resonance fluorescence, chemical titration,   \nl
R. Stimpfle, & UC-Berkeley & & & and thermal dissociation\nl
R. Cohen & & &, NO$_2$ & Laser-induced fluorescence \nl
\nl

E. Atlas & NCAR & WAS & hydrocarbons, &  Whole air canister sample with laboratory \nl
 & & & halocarbons, & analysis by gas chromatography and mass \nl
 & & & organic nitrates & spectrometry\nl
 
K. Boering, & Harvard & CO$_2$ & CO$_2$ & Non-dispersive infrared absorption \nl
S. Wofsy \nl
\nl

P. Bui & NASA ARC & MMS & pressure, winds, & External aircraft probes and pressure \nl
 & & & temperature & ports \nl

J. Elkins & NOAA CMDL & ACATS & CFC-11, CFC-12, & Gas chromatography, electron capture \nl
& & & CFC-13, CH$_3$CCl$_3$, & detection \nl
& & & CCl$_4$, Halon 1211, & \nl
& & & SF$_6$, H$_2$, N$_2$O, CH$_4$ & \nl

B. Gandrud & NCAR & MASP & particle number and size & Light scattering by individual particles\nl
 & & & (0.4--10 $\mu$m diameter)\nl


R.-S. Gao & NOAA AL & NO$_y$ & NO, NO$_2$, NO$_y$ & NO-O$_3$ chemiluminescence combined with \nl 
 & & & & photolysis for NO$_2$, catalysis for NO$_y$ \nl

B. Gary & NASA JPL & MTP & temperature profiler & Microwave radiometer\nl
\nl
M. Loewenstein & NASA ARC & ATLAS & N$_2$O & Tunable diode laser absorption\nl
\nl
R. May & NASA JPL & H$_2$O & H$_2$O & Open path, far-infrared absorption \nl
\nl
C. T. McElroy & AES, Canada & CPFM & solar radiation & UV and visible spectroradiometer\nl
\nl

M. Proffitt & NOAA AL & O$_3$ & O$_3$ & Ultraviolet light absorption \nl
\nl

R. Stachnik & NASA JPL & SLS & O$_3$, H$_2$O, HNO$_3$, ClO & Submillimeter-wave emission spectroscopy\nl
\nl
A. Strawa & NASA ARC & APS & particle number and size & Wire impaction and electron microscope \nl
 & & & ($>$0.1 $\mu$m diameter) & analysis\nl


C. Webster & NASA JPL & ALIAS & HCl, N$_2$O, CH$_4$, CO & Tunable diode laser absorption \nl
\nl

J. Wilson & Denver & CNC & condensation nuclei & Particle growth followed by light \nl
 & & & particles & scattering \nl


J. Wilson & Denver & FCAS & particle number and size & Light scattering by individual particles\nl
 & & & (0.08--2 $\mu$m diameter)\nl
\end{planotable}

\begin{planotable}{lllll}
\tablewidth{41pc}
\tablecaption{POLARIS OMS Balloon Observations}
\tablenum{3}
\tablehead{PI & Institution & Instrument & Measurements & Technique }
\label{table:tbl-3}

\startdata
\cutinhead{in-situ} \nl

K. Boering, & Harvard & CO$_2$ & CO$_2$ & Non-dispersive infrared absorption\nl
S. Wofsy \nl
\nl
J. Elkins & NOAA CMDL & LACE & CFC-11, CFC-12,  & Gas chromatography with electron \nl
 & & &CFC-13, SF$_6$ & capture detection\nl
\nl
M. Loewenstein & NASA ARC & ARGUS & N$_2$O, CH$_4$ & Tunable diode laser absorption \nl
\nl
J. Margitan & NASA JPL & O$_3$ & O$_3$ & Ultraviolet absorption\nl
\nl
S. Oltmans & NOAA CMDL & H$_2$O & H$_2$O & Frost-point hygrometer\nl
\nl
C. Webster & NASA JPL & ALIAS II & N$_2$O, CH$_4$ & Tunable diode laser absorption \nl
\cutinhead{remote} \nl
G. Toon & NASA JPL & MkIV & O$_3$, N$_2$O, HNO$_3$, NO$_2$, CH$_4$, & Solar infrared absorption \nl
 & & & H$_2$O, CO, CFC-11, N$_2$O$_5$, \nl
 & & & H$_2$O$_2$, HOCl, ClONO$_2$, HCl, \nl
 & & & HF, CFC-12, NO, HNO$_4$, \nl
 & & & OCS, HCN, CCl$_4$, CF$_4$, COF$_2$, \nl
 & & & CHFCl$_2$, CH$_3$Cl, C$_2$H$_2$, C$_2$H$_6$, \nl
 & & & O$_2$, N$_2$, H$_2$CO, HCOOH,  \nl
 & & & HDO, SF$_6$, CFC-113, CH$_3$Cl   \nl
J. Margitan & NASA JPL & O$_3$ & O$_3$ & Ultraviolet absorption\nl


\end{planotable}

\begin{planotable}{lllll}
\tablewidth{41pc}
\tablecaption{POLARIS Collaborative Measurement Programs and Platforms}
\tablenum{4}
\tablehead{PI & Institution & Instrument & Measurements & Technique/ \\
 & & & & Satellite }
\label{table:tbl-4}

\startdata
\cutinhead{ADEOS Correlative Balloon Measurement -- 30 April 1997} \nl
M. Hayashi & Nagoya & Aerosol & particle size and number & Filter/impactor measurements\nl
\nl
J. Margitan & NASA JPL & O$_3$ & O$_3$ & Ultraviolet absorption\nl
\nl
R. Stachnik & NASA JPL & SLS & O$_3$, N$_2$O, HNO$_3$, HO$_2$, ClO, & Submillimeter limb sounder \nl
& & & HCl \nl
\nl
W. Traub & SAO & FIRS-2 & O$_3$, N$_2$O, HNO$_3$, NO$_2$, H$_2$O, & Far-infrared spectrometer \nl
 & & & N$_2$O$_5$, OH, HO$_2$, H$_2$O$_2$, \nl
 & & & HOCl, ClONO$_2$, HCl, HF\nl
\nl
\cutinhead{ADEOS Correlative Balloon Measurement -- 8 May 1997} \nl

F. Murcray & Denver & CAESR & O$_3$, HNO$_3$, CH$_4$, CFC-11, & Mid-infrared remote thermal emission \nl
 & & & CFC-12, N$_2$O$_5$, aerosol & grating spectrometer\nl
\nl
G. Toon & NASA JPL & MkIV & CO$_2$ and 22 of the 33 & Solar infrared absorption \nl
  &  &  &  species listed in table 3 \nl
M. Hayashi & Nagoya & Aerosol & particle size and number & Filter/impactor measurements\nl
\nl

\cutinhead{POLARIS correlative ground and ozonesonde measurements} \nl
D. Jaffe   & U. Alaska & ozonesondes & P, T, O$_3$ & Electrochemical cell\nl
S. Oltmans & NOAA CMDL\nl
\nl
C. T. McElroy &  AES, Canada   & Brewer & O$_3$ & UV spectra \nl
\nl
R. Benner  &  U. Alaska & Dobson & O$_3$ & Differential UV \nl
\nl
G. Toon & NASA JPL & MkIV & See table 3 & Solar infrared absorption \nl
\nl

\cutinhead{POLARIS Satellite Measurement Investigators} \nl
P. McCormick & Hampton & SAGE II & NO$_2$, aerosols & ERBS \nl
\nl
R. McPeters & NASA GSFC & TOMS & column O$_3$ & Earth Probe \nl
\nl
R. Pierce & NASA LaRC & HALOE & O$_3$, NO, NO$_2$, H$_2$O, CH$_4$, & UARS\nl
 & & & HCl, HF\nl
\nl
R. Pierce & NASA LaRC & MLS & O$_3$, HNO$_3$, ClO & UARS\nl
\nl
Y. Sasano & JAE/NIES & ILAS & O$_3$, HNO$_3$, NO$_2$, N$_2$O, H$_2$O, & ADEOS \nl
 & & & CFC-11, CH$_4$, aerosols\nl
\end{planotable}


\begin{planotable}{lllll}
\tablewidth{41pc}
\tablecaption{POLARIS Modeling and Forecast Projects}
\tablenum{5}
\tablehead{PI & Institution & Project Description }

\startdata
\label{table:tbl-5}
B. Brune    & Penn State & OMS project scientist\nl
\nl
D. Fahey    & NOAA AL & POLARIS co-project scientist\nl
\nl
M. Hitchman & Wisconsin & Non-Hydrostatic modeling of summer stratospheric mixing processes\nl
\nl
R. Kawa & NASA GSFC & 3-D chemical transport and chemistry on trajectory modeling \nl
 &  & AEAP Program scientist \nl
\nl
M. Ko & AER, Inc. & Contribution to data analysis using AER 2-D assessment model \nl
\nl
M. Kurylo  & NASA HQ & UARP manager and POLARIS program scientist\nl
           & NIST    & \nl
\nl
S. Lloyd & Johns Hopkins & Radiative and photochemical modeling \nl
\nl
P. Newman  & NASA GSFC & POLARIS co-project scientist \nl
           &           & Meteorological forecasting, flight planning, and data analysis\nl
\nl
L. Pfister & NASA ARC & Meteorological satellite data support \nl
\nl
R. Pierce & NASA LaRC & HALOE airmass trajectory and photochemical modeling \nl
\nl
R. Salawitch & NASA JPL & Photochemical steady state modeling \nl
\nl
S. Solomon & NOAA AL & Interpretation of observations using a 2-D model \nl
\nl
S. Strahan & NASA GSFC & Flight planning and constituent modeling using the GEOS-1 \nl
 & & data assimilation system \nl
\nl
A. Tuck & NOAA AL & SAGE II and HALOE data analysis and modeling \nl
\nl
D. Waugh & Monash & CRC-SHM meteorological support and chemical modeling\nl
 
\nl
S. Wofsy & Harvard & Analysis of ozone changes using SAGE II data and trajectories \nl
\end{planotable}

\clearpage


\end{document}


