Catalogo Articoli (Spogli Riviste)

OPAC HELP

Titolo:
Postfrontal airmass modification
Autore:
Freedman, JM; Fitzjarrald, DR;
Indirizzi:
SUNY Albany, Atmospher Sci Res Ctr, Albany, NY 12222 USA SUNY Albany Albany NY USA 12222 mospher Sci Res Ctr, Albany, NY 12222 USA
Titolo Testata:
JOURNAL OF HYDROMETEOROLOGY
fascicolo: 4, volume: 2, anno: 2001,
pagine: 419 - 437
SICI:
1525-755X(2001)2:4<419:PAM>2.0.ZU;2-Y
Fonte:
ISI
Lingua:
ENG
Soggetto:
ATMOSPHERIC BOUNDARY-LAYER; WATER-VAPOR EXCHANGE; PHASEOLUS-VULGARIS L; DECIDUOUS FOREST; CARBON-DIOXIDE; SURFACE FLUXES; PARAMETERIZATION; DYNAMICS; MODELS; FIFE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
68
Recensione:
Indirizzi per estratti:
Indirizzo: Freedman, JM Atmospher Informat Serv, 251 Fuller Rd, Albany, NY 12203 USA Atmospher Informat Serv 251 Fuller Rd Albany NY USA 12203 USA
Citazione:
J.M. Freedman e D.R. Fitzjarrald, "Postfrontal airmass modification", J HYDROMETE, 2(4), 2001, pp. 419-437

Abstract

The northeastern United States is subject to relatively frequent passages of frontal systems during the growing season. After a frontal passage, the newly arrived air mass is gradually modified by the underlying, mostly vegetated landscape. For the 1995-98 growing seasons, 25 frontal sequences withat least 4 days between frontal passages were identified; 16 had sufficient data continuity for rigorous analysis. A composite of sequences featuringthe daily appearance of boundary layer cumulus clouds (BLcu) indicates a diminished role for entrainment and other external forcings because of the daily occurrence of a rapid growth phase in the mixed-layer (ML) diurnal evolution subsequent to day 1. Between frontal passages, net heat and moistureflux convergence in the ML is near zero, but during the warming and moistening phase, the surface flux terms, through a net radiation-BLcu feedback, are the principal controls on the tendencies of the ML temperature theta and specific humidity q. The combination of the theta and q tendencies leads to a nearly constant lifting condensation level, relative humidity, and BLcu cloud fraction during the latter part of the sequences. The presence of BLcu enhances water use efficiency and net afternoon carbon uptake throughout the sequence, with day 4 featuring optimal conditions. A multiday box model was used to perform sensitivity studies on subsidence, the lapse rate gamma (theta nu) above the ML, cloud mass flux, and the regional surface Bowen ratio beta (reg). The effects of subsidence and gamma (theta nu) on ML processes are most conspicuous on day 1; during subsequent days, the rapid growth phase dominates the ML growth equation and reduces the impact of theseexternal terms. Increasing beta (reg) to 3.5 reduces BLcu fraction to lessthan 20% and produces little net moistening of the ML, whereas reducing beta (reg) by 30% increases sequence BLcu coverage by 30%-80%. In sum, the presence of a net radiation-BLcu feedback allows for the establishment of an equilibrium in the ML heat and moisture tendencies and ensures the appearance of BLcu on each day of the sequence, thus sustaining favorable conditions for forest-atmosphere exchange (i.e., carbon uptake).

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 05/12/20 alle ore 14:12:44