Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Modeling the large-scale structure of a barchan dune field   In nature, barchan dunes typically exist as members of larger fields that
display striking, enigmatic structures that cannot be readily explained by
examining the dynamics at the scale of single dunes, or by appealing to
patterns in external forcing. To explore the possibility that observed
structures emerge spontaneously as a collective result of many dunes
interacting with each other, we built a numerical model that treats barchans as
discrete entities that interact with one another according to simplified rules
derived from theoretical and numerical work and from field observations: (1)
Dunes exchange sand through the fluxes that leak from the downwind side of each
dune and are captured on their upstream sides; (2) when dunes become
sufficiently large, small dunes are born on their downwind sides (`calving');
and (3) when dunes collide directly enough, they merge. Results show that these
relatively simple interactions provide potential explanations for a range of
field-scale phenomena including isolated patches of dunes and heterogeneous
arrangements of similarly sized dunes in denser fields. The results also
suggest that (1) dune field characteristics depend on the sand flux fed into
the upwind boundary, although (2) moving downwind, the system approaches a
common attracting state in which the memory of the upwind conditions vanishes.
This work supports the hypothesis that calving exerts a first-order control on
field-scale phenomena; it prevents individual dunes from growing without bound,
as single-dune analyses suggest, and allows the formation of roughly realistic,
persistent dune field patterns.

12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph