Atmospheric Modeling | ScienceGate

Abstract Summer simulations over the contiguous United States and Mexico with the Regional Atmospheric Modeling System (RAMS) dynamically downscaling the NCEP–NCAR Reanalysis I for the period 1950–2002 (described in Part I of the study) are evaluated with respect to the three dominant modes of global SST. Two of these modes are associated with the statistically significant, naturally occurring interannual and interdecadal variability in the Pacific. The remaining mode corresponds to the recent warming of tropical sea surface temperatures. Time-evolving teleconnections associated with Pacific SSTs delay or accelerate the evolution of the North American monsoon. At the period of maximum teleconnectivity in late June and early July, there is an opposite relationship between precipitation in the core monsoon region and the central United States. Use of a regional climate model (RCM) is essential to capture this variability because of its representation of the diurnal cycle of convective rainfall. The RCM also captures the observed long-term changes in Mexican summer rainfall and suggests that these changes are due in part to the recent increase in eastern Pacific SST off the Mexican coast. To establish the physical linkage to remote SST forcing, additional RAMS seasonal weather prediction mode simulations were performed and these results are briefly discussed. In order for RCMs to be successful in a seasonal weather prediction mode for the summer season, it is required that the GCM provide a reasonable representation of the teleconnections and have a climatology that is comparable to a global atmospheric reanalysis.

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Large Temperature Fluctuations due to Cold-Air Pool Displacement along the Lee Slope of a Desert Mountain

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-16-0202.1 ◽

2017 ◽

Vol 56 (4) ◽

pp. 1083-1098 ◽

Cited By ~ 5

Author(s):

Matthew E. Jeglum ◽

Sebastian W. Hoch ◽

Derek D. Jensen ◽

Reneta Dimitrova ◽

Zachariah Silver

Keyword(s):

Low Frequency ◽

Temperature Fluctuations ◽

Atmospheric Modeling ◽

Large Temperature ◽

Complex Flow ◽

Near Surface ◽

Cold Air ◽

Flow Interactions ◽

Initial Drop ◽

Program Temperature

AbstractLarge temperature fluctuations (LTFs), defined as a drop of the near-surface temperature of at least 3°C in less than 30 min followed by a recovery of at least half of the initial drop, were frequently observed during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) program. Temperature time series at over 100 surface stations were examined in an automated fashion to identify and characterize LTFs. LTFs occur almost exclusively at night and at locations elevated 50–100 m above the basin floors, such as the east slope of the isolated Granite Mountain (GM). Temperature drops associated with LTFs were as large as 13°C and were typically greatest at heights of 4–10 m AGL. Observations and numerical simulations suggest that LTFs are the result of complex flow interactions of stably stratified flow with a mountain barrier and a leeside cold-air pool (CAP). An orographic wake forms over GM when stably stratified southwesterly nocturnal flow impinges on GM and is blocked at low levels. Warm crest-level air descends in the lee of the barrier, and the generation of baroclinic vorticity leads to periodic development of a vertically oriented vortex. Changes in the strength or location of the wake and vortex cause a displacement of the horizontal temperature gradient along the slope associated with the CAP edge, resulting in LTFs. This mechanism explains the low frequency of LTFs on the west slope of GM as well as the preference for LTFs to occur at higher elevations later at night, as the CAP depth increases.

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Coupling between Large-Scale Atmospheric Processes and Mesoscale Land–Atmosphere Interactions in the U.S. Southern Great Plains during Summer. Part II: Mean Impacts of the Mesoscale

Journal of Hydrometeorology ◽

10.1175/jhm-397.1 ◽

2004 ◽

Vol 5 (6) ◽

pp. 1247-1258 ◽

Cited By ~ 21

Author(s):

Christopher P. Weaver

Keyword(s):

Case Studies ◽

Time Scales ◽

Great Plains ◽

Large Scale ◽

Spatial Scales ◽

Surface Heterogeneity ◽

Atmospheric Modeling ◽

Mesoscale Circulations ◽

Southern Great Plains ◽

Atmospheric Processes

Abstract This is Part II of a two-part study of mesoscale land–atmosphere interactions in the summertime U.S. Southern Great Plains. Part I focused on case studies drawn from monthlong (July 1995–97), high-resolution Regional Atmospheric Modeling System (RAMS) simulations carried out to investigate these interactions. These case studies were chosen to highlight key features of the lower-tropospheric mesoscale circulations that frequently arise in this region and season due to mesoscale heterogeneity in the surface fluxes. In this paper, Part II, the RAMS-simulated mesoscale dynamical processes described in the Part I case studies are examined from a domain-averaged perspective to assess their importance in the overall regional hydrometeorology. The spatial statistics of key simulated mesoscale variables—for example, vertical velocity and the vertical flux of water vapor—are quantified here. Composite averages of the mesoscale and large-scale-mean variables over different meteorological or dynamical regimes are also calculated. The main finding is that, during dry periods, or similarly, during periods characterized by large-scale-mean subsidence, the characteristic signature of surface-heterogeneity-forced mesoscale circulations, including enhanced vertical motion variability and enhanced mesoscale fluxes in the lowest few kilometers of the atmosphere, consistently emerges. Furthermore, the impact of these mesoscale circulations is nonnegligible compared to the large-scale dynamics at domain-averaged (200 km × 200 km) spatial scales and weekly to monthly time scales. These findings support the hypothesis that the land– atmosphere interactions associated with mesoscale surface heterogeneity can provide pathways whereby diurnal, mesoscale atmospheric processes can scale up to have more general impacts at larger spatial scales and over longer time scales.

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Idealized large-eddy simulations of stratocumulus advecting over cold water. Part 1: Boundary layer decoupling

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-21-0108.1 ◽

2021 ◽

Author(s):

Youtong Zheng ◽

Haipeng Zhang ◽

Daniel Rosenfeld ◽

Seoung-Soo Lee ◽

Tianning Su ◽

...

Keyword(s):

Boundary Layer ◽

Surface Temperature ◽

Cold Water ◽

Temperature Inversion ◽

Atmospheric Modeling ◽

Sea Surface ◽

Entrainment Rate ◽

Surface Cooling ◽

Near Surface ◽

Large Eddy

AbstractWe explore the decoupling physics of a stratocumulus-topped boundary layer (STBL) moving over cooler water, a situation mimicking the warm air advection (WADV). We simulate an initially well-mixed STBL over a doubly periodic domain with the sea surface temperature decreasing linearly over time using the System for Atmospheric Modeling large-eddy model. Due to the surface cooling, the STBL becomes increasingly stably stratified, manifested as a near-surface temperature inversion topped by a well-mixed cloud-containing layer. Unlike the stably stratified STBL in cold air advection (CADV) that is characterized by cumulus coupling, the stratocumulus deck in the WADV is unambiguously decoupled from the sea surface, manifested as weakly negative buoyancy flux throughout the sub-cloud layer. Without the influxes of buoyancy from the surface, the convective circulation in the well-mixed cloud-containing layer is driven by cloud-top radiative cooling. In such a regime, the downdrafts propel the circulation, in contrast to that in CADV regime for which the cumulus updrafts play a more determinant role. Such a contrast in convection regime explains the difference in many aspects of the STBLs including the entrainment rate, cloud homogeneity, vertical exchanges of heat and moisture, and lifetime of the stratocumulus deck, with the last being subject to a more thorough investigation in part 2. Finally, we investigate under what conditions a secondary stratus near the surface (or fog) can form in the WADV. We found that weaker subsidence favors the formation of fog whereas a more rapid surface cooling rate doesn’t.

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Atmospheric Modeling: Numerical Weather Prediction . George J. Haltiner. Wiley, New York, 1971. xviii, 318 pp., illus. $10.95.

Science ◽

10.1126/science.175.4027.1235-a ◽

1972 ◽

Vol 175 (4027) ◽

pp. 1235-1235

Author(s):

Yoshio Kurihara

Keyword(s):

New York ◽

Numerical Weather Prediction ◽

Weather Prediction ◽

Atmospheric Modeling ◽

Numerical Weather

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Atmospheres on Callisto composed of sublimated water vapor and its photochemical products

10.5194/epsc2021-3 ◽

2021 ◽

Author(s):

Shane Carberry Mogan ◽

Orenthal Tucker ◽

Robert Johnson ◽

Audrey Vorburger ◽

Andre Galli ◽

...

Keyword(s):

Monte Carlo ◽

Near Infrared ◽

Hubble Space Telescope ◽

Mass Movement ◽

Complex Surface ◽

Atmospheric Modeling ◽

Galilean Satellites ◽

Geophysical Research ◽

Water Ice ◽

Remote Determination

The parameter space for the very uncertain composition of sublimated H2O and its photochemical products H and H2 in Callisto's atmosphere is examined using the Direct Simulaton Monte Carlo (DSMC) method. We focus on two significantly different versions of H2O production in which: (1) the ice and dark, non-ice/ice-poor material are intimately mixed and H2O sublimates at Callisto's warm day-side temperatures (e.g., as in most atmospheric modeling efforts at Callisto to date [1-4]); and (2) the ice and dark, non-ice/ice-poor material are segregated (e.g., consistent with interpretations of images of Callisto's surface taken by Voyager [5, 6] and Galileo [7]) and H2O sublimates at "ice" temperatures [8]. Our 2D molecular kinetic models track the motion H2O, whose sublimation yield varies several orders of magnitude depending on the description of Callisto's surface, its photochemical products H and H2, and a relatively dense O2 component. Whereas H is assumed to react in the regolith on return to the surface, H2 is assumed to thermalize and re-enter the atmosphere. We compare the simulated LOS column densities of H to the detected H corona at Callisto [9], which was suggested to be produced primarily by photodissociation of sublimated H2O. Our goal is to use the corona observations to help constrain the source rate for H2O from Callisto&#8217;s complex surface. References [1] Liang et al., 2005. Atmosphere of Callisto. Journal of Geophysical Research: Planets. [2] Vorburger et al., 2015. Monte-Carlo simulation of Callisto&#8217;s exosphere. Icarus. [3] Hartkorn et al., 2017. Structure and density of Callisto&#8217;s atmosphere from a fluid-kinetic model of its ionosphere: Comparison with Hubble Space Telescope and Galileo observations. Icarus. [4] Carberry Mogan et al., 2021 (under review). A tenuous, collisional atmosphere on Callisto. Icarus. [5] Spencer and Maloney, 1984. Mobility of water ice on Callisto: Evidence and implications. Geophysical Research Letters. [6] Spencer, 1987. Thermal segregation of water ice on the Galilean satellites. Icarus. [7] Moore et al., 1999. Mass movement and landform degradation on the icy Galilean satellites: Results of the Galileo nominal mission. Icarus. [8] Grundy et al., 1999. Near-infrared spectra of icy outer solar system surfaces: Remote determination of H2O ice temperatures. Icarus. [9] Roth et al., 2017. Detection of a hydrogen corona at Callisto. Journal of Geophysical Research: Planets.

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Atmospheric Modeling: Numerical Weather Prediction . George J. Haltiner. Wiley, New York, 1971. xviii, 318 pp., illus. $10.95.

Science ◽

10.1126/science.175.4027.1235.a ◽

1972 ◽

Vol 175 (4027) ◽

pp. 1235-1235

Author(s):

Yoshio Kurihara

Keyword(s):

New York ◽

Numerical Weather Prediction ◽

Weather Prediction ◽

Atmospheric Modeling ◽

Numerical Weather

Download Full-text