2.a. Curtain plots
The spatial structures and variability of P-O3 as sampled by the ATom
transects over the Pacific Ocean are presented in Figure 1a. The full
set of plots covering all three reactivities and also the Atlantic Ocean
are shown in Supplementary Figures S3-S8. For these curtain plots, the
10 s reactivities (2 km by 80 m thick parcels) are averaged and plotted
in 1° latitude by 200 m thick cells. In August (ATom-1), the highly
reactive (hot) P-O3 parcels (3.5
to 6+ ppb/day) are common throughout most of the lower troposphere (0-5
km) from 20°S to 60°N, and there is also a region of very high P-O3 in
the upper northern tropics (8-12 km, 15°N-30°N). In February (ATom-2),
P-O3 shifts to the southern mid-latitude and tropics following the
overhead sun as expected, but the tropical production lacks the
intensity seen in ATom-1 in the 20°N-30°N region. In October (ATom-3)
the high P-O3 parcels are primarily tropical, but favor the southern
latitudes. Finishing in May (ATom-4) we find the northern dominance
returns although not as strongly as in ATom-1 and find some regions of
P-O3 > 5 ppb/day as also in ATom-1. Overall, this shows the
dominance of the tropics for production of O3 over the
oceans. The northern summer mid-latitudes almost contribute a fifth
tropical season, and all of the highly reactive regions probably show
the importance of deep convection over northern continents influencing
the tropical Pacific in August and May. The loss of O3shows similar seasonal shifts as P-O3, following the sun especially in
the tropics, and moving into the northern mid-latitudes in August and
May, but high reactivities are limited to below 8 km. The loss of
CH4 parallels that of O3.
In the Atlantic P-O3 also follows the sun, with high reactivity south of
the equator for February (ATom-2) and October (ATom-3). In August
(ATom-1), a substantial number of air parcels show high P-O3 (2-6
ppb/day) from 10°S to 45°N. There is a cluster of hot parcels in the
lower troposphere (1-5 km) but also a clustering in the upper
troposphere (6-12 km), including about 20°S in May (ATom-4). We know
that the tropical Atlantic O3 is influenced by
continental outflow of biomass burning from South America and Africa
(Fishman et al., 1990), and here we see that outflow is actively
producing O3. L-O3 occurs in a more tightly constrained
region than P-O3, both in latitude and altitude (0-6 km). L-O3 is
centered on the tropics for all Atom-1234 but, like in the Pacific, it
includes a highly reactive region in northern summer mid-latitudes
(30°N-50°N, ATom-1). The Atlantic pattern of L-CH4 is almost identical
to that of L-O3, but peaks about 1 km lower in altitude.
Given the importance of the tropics in the global reactivity of the
atmosphere, we create expanded 30°S-30°N curtain profiles and separate
the Pacific into Central (about 180°E-210°E) and Eastern (about 240°E,
the first flight of each deployment from Palmdale CA south to the
equator and back) (Figures S9-S17). The expanded plots clearly show the
patchy nature of P-O3 hot spots in the Central Pacific and the Atlantic
(except for 15°S-25°S, 7-9 km), while emphasizing the large coherent hot
spots in L-O3 and L-CH4 in the Atlantic. The Eastern Pacific stands out:
there are large coherent regions (20° by 2-3 km) associated with well
mixed convective outflow from North America having extreme reactivities
in August (monsoonal) and May (possibly biomass burning).
Curtain profiles for the Arctic (Figure S18) are presented only for
ATom-1 and ATom-4 when there was enough sunlight to generate
non-negligible reactivities. The stratospheric air parcels are excluded.
Reactivities appear moderately high, but the color scale here is 3 times
smaller than in Figures S3-S17. In the Arctic, much of the P-O3 occurs
above 6 km, and L-CH4 is suppressed relative to L-O3 because of the
colder temperatures. Only one of the two Antarctic flights had enough
sunlight to produce much reactivity (ATom-3, Figures S19). Like the
Arctic, P-O3 is in the upper troposphere, while L-O3 and L-CH4 are in
the lower. Note that the color scale is 6-to-12 times smaller than in
Figures S3-17.