Propósito del Juego

To understand how the trajectory origin density fields relate to Q · ˆn the density fields, ρ(x), are weighted by (1/g)qv · ˆnd˜pdl from each trajectory:

Q · ˆn(x) = 1 g n X i=1 (qv · ˆnd˜pdl)i Ki(x) (5.12)

Figure 5.11: Proportions of all trajectories released from each catchment boundary with origin in the Atlantic (red), Indian (dark blue), Pacific (green), Arctic (pink), Southern (gold) drainage basins, stratosphere (light blue) or without origin (white). Only proportions of 3% or greater are labelled. The total number of trajectories (n) released from each catchment boundary over 2010-2014 is shown in each panel.

after Hodges (1996). The flux-weighted density maps for trajectories released from the catch- ment boundaries surrounding each of the five drainage basins (Figure 5.10) are shown in Fig- ures 5.12-5.16 where blue/negative contours indicate moisture flux leaving the drainage basin (therefore reducing P − E) and red/positive contours indicate moisture flux which is entering the drainage basin (therefore increasing P − E). For brevity, only the flux-weighted density maps for all trajectories with origin are shown rather than separate CAT I and CAT II maps.

Chapter 5: Using trajectories to understand the atmospheric moisture budget asymmetries 121

Figure 5.12: Flux-weighted density maps for all trajectories with origin released from catch- ment boundaries surrounding the Atlantic drainge basin: (a) Americas, (b) Africa, (c) Arctic Atlantic and (d) Southern Atlantic. Red/positive contours indicate moisture flux entering the basin across the catchment boundary and blue/negative contours indicate moisture flux leav- ing the basin across the catchment boundary.

particularly along the African catchment boundary, as would be expected from the trajectory origin density maps (Figures 5.7). The effect of coastal outflow can also be seen in the flux- weighted density maps, particularly along the South American and Indian coasts. The sub- tropical highs show up as regions with low to zero flux-weighted density where air is moving away from the catchment boundaries e.g. North Pacific for American catchment boundary, and South Atlantic for African catchment boundary. The northern hemisphere storm tracks are also clearly identifiable as narrow bands of 10-25 kg s−1 steradian−1 density across the North At- lantic and Pacific Oceans. Remote moisture origins appear to be very scarce with only small regions of low flux-weighted density notable in Figures 5.12-5.16 e.g. in the North Atlantic for eastward Q · ˆnacross South-East Asia, and in the South Pacific for eastward Q · ˆnacross Africa.

Some key features of the flux-weighted density fields specific to each basin are:

1. Atlantic Ocean (Figure 5.12): The North Pacific storm track imports moisture across North America and the North Atlantic storm track exports moisture across Europe. High

Figure 5.13: Flux-weighted density maps for all trajectories with origin released from catch- ment boundaries surrounding the Indian drainge basin: (a) Africa, (b) South-East Asia, (c) Arctic Indian and (d) Southern Indian. Red/positive contours indicate moisture flux entering the basin across the catchment boundary and blue/negative contours indicate moisture flux leaving the basin across the catchment boundary.

flux-weighted densities are found across the Caribbean Sea and tropical North Atlantic (similar to Duran-Queseda et al., 2010) for westward Q · ˆnacross Central America which shows that the moisture transported from the Atlantic to the Pacific does indeed have ori- gin in this region (Broecker, 1991; Leduc et al., 2007). However, this methodology cannot directly link Q · ˆnto Pacific precipitation.

2. Indian Ocean (Figure 5.13): For trajectories released from the South-East Asian catchment boundary, there is a narrow band of very low flux-weighted density off the coast of East Africa and the Arabian peninsula highlighting the path of the Somali LLJ. Flux-weighted density for Q · ˆn leaving the Indian Ocean basin is greatest across the Bay of Bengal for trajectories released from the South Easr Asian catchment boundary, and east of Mada- gascar for trajectories released from the Indian sector of the Southern Ocean catchment boundary.

3. Pacific Ocean (Figure 5.14): The North Pacific storm track exports moisture across the northern end of the American catchment boundary and the eastern end of the Arctic

Chapter 5: Using trajectories to understand the atmospheric moisture budget asymmetries 123

Figure 5.14: Flux-weighted density maps for all trajectories with origin released from catch- ment boundaries surrounding the Pacific drainge basin: (a) South-East Asia, (b) Americas, (c) Arctic Pacific and (d) Southern Pacific. Red/positive contours indicate moisture flux entering the basin across the catchment boundary and blue/negative contours indicate moisture flux leaving the basin across the catchment boundary.

(Pacific sector) catchment boundary with a weak import of moisture across Asia with origin from the North Atlantic storm track. Most of the South Pacific is occupied by a region of high flux-weighted density for southward Q · ˆnacross 35◦S.

4. Arctic Ocean (Figure 5.15): The North Atlantic and North Pacific storm tracks import moisture to the Arctic, hence the dominance of transient moisture fluxes in the Arctic moisture budget (section 4.2.2). Across the Indian sector of the Arctic catchment bound- ary, Q · ˆninto the Arctic has low-density origin across the subtropical North Atlantic and North Africa with higher densities around the Arabian peninsula.

5. Southern Ocean (Figure 5.16): High flux-weighted densities are found in the poleward part of the southern hemisphere subtropical highs. The contrasting shapes of these re- gions are a result of the differences in q v between the basins (Figure 4.7(d)). Moisture fluxes leaving the Southern Ocean basin generally have origin within 20◦ latitude of the catchment boundary with the Q · ˆn extending around the Southern Ocean, sometimes into the neighbouring basins.

Figure 5.15: Flux-weighted density maps for all trajectories with origin released from catch- ment boundaries surrounding the Arctic drainge basin: (a) Atlantic sector, (b) Indian sector and (c) Pacific sector. Red/positive contours indicate moisture flux entering the basin across the catchment boundary and blue/negative contours indicate moisture flux leaving the basin across the catchment boundary.