Validation of the Coupled NCEP Mesoscale Spectral Model and an Advanced Land Surface Model over the Hawaiian Islands. Part II: A High Wind Event*

2005 ◽  
Vol 20 (6) ◽  
pp. 873-895 ◽  
Author(s):  
Yongxin Zhang ◽  
Yi-Leng Chen ◽  
Kevin Kodama
Keyword(s):  
Land Surface ◽  
Cold Front ◽  
Hawaiian Islands ◽  
Land Surface Model ◽  
Trade Wind ◽  
Surface Model ◽  
High Wind ◽  
Wind Event ◽  
Trade Wind Inversion ◽  
Downslope Windstorms

Abstract A high wind event (14–15 February 2001) over the Hawaiian Islands associated with a cold front is simulated using the National Centers for Environmental Prediction (NCEP) Mesoscale Spectral Model (MSM) coupled with an advanced land surface model (LSM). During this period, a strong high pressure cell moved to the northeast of the Hawaiian Islands following the passage of the cold front. The cell then merged with the semipermanent subtropical high and resulted in windy conditions across the state of Hawaii. Analyses of soundings from Lihue on Kauai and Hilo on the Big Island reveal a mean-state critical level below 400 hPa, a strong cross-barrier flow (∼13 m s−1), and the presence of a trade wind inversion. The MSM–LSM predicts downslope windstorms on the lee sides of mountains or ridges with tops beneath the trade wind inversion and within ocean channels between islands. In the case of high mountains with a peak height above the trade wind inversion, weak winds are simulated on the lee side. Around the corners of the islands and in gaps between mountains, gap winds and downslope windstorms are both important for the development of localized leeside windstorms. The localized windstorms over the Hawaiian Islands develop as a result of interactions between large-scale airflow and the complex local topography. Since the terrain is not adequately resolved by the 10-km RSM–LSM, it is no surprise that these windstorms are better simulated by the high-resolution nonhydrostatic MSM–LSM than the 10-km RSM–LSM.

scholarly journals Effects of Trade-Wind Strength and Direction on the Leeside Circulations and Rainfall of the Island of Hawaii

2008 ◽  
Vol 136 (12) ◽  
pp. 4799-4818 ◽  
Author(s):  
Yang Yang ◽  
Yi-Leng Chen ◽  
Francis M. Fujioka
Keyword(s):  
Potential Vorticity ◽  
Land Surface ◽  
Mesoscale Model ◽  
Land Surface Model ◽  
Coastal Region ◽  
Trade Wind ◽  
Surface Model ◽  
Katabatic Flow ◽  
Reversed Flow ◽  
Trade Wind Inversion

Abstract The leeside circulations and weather of the island of Hawaii were studied from the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) land surface model simulations for eight strong (∼7.9 m s−1) and eight weak (∼5.2 m s−1) trade-wind days and for five days with southeasterly trades (∼7.1 m s−1) during summer 2004. The objective is to investigate the effects of trade-wind strength and directions on the leeside circulations and rainfall and the modification of these effects by the land surface thermal forcing. For the small wake on the lee side of the Kohala Mountains (1700 m, lower than the trade-wind inversion at 2000 m) over northern Hawaii, the hydraulic jump is present with stronger downslope winds and warmer and drier conditions on the lee side and a weaker westerly reversed flow offshore when trades are stronger. In contrast, the westerly reversed flow along the large wake axis off the central Kona leeside coast (behind massive mountains with tops >4000 m) is 1–1.5 m s−1 stronger and 200–300 m deeper with higher moisture content when trades are stronger. Over the Kona slopes, the daytime thermally direct circulation cell is more significant when trades are stronger because of descending airflow aloft with less cloudiness. In the evening, the convergence between the westerly reversed flow offshore along the wake axis and the offshore/katabatic flow in the Kona coastal region is more significant with higher evening rainfall when trades are stronger. During the day, the lee side of the Kohala Mountains is characterized by a reversed flow (∼4 m s−1) merging with sea-breeze circulations along the coast. When trades are stronger, the convergence between the anabatic winds and the descending flow from the upper slopes is greater. However, the simulated cloud water there is less under strong trades because of warmer and drier conditions due to significant adiabatic descent in the lee. At night, when trades are stronger, the combined downslope/katabatic flow prevails without a reversed flow offshore. Under a southeasterly trade-wind flow with a lower trade-wind inversion (1.5 km), the westerly reversed flow is shallower; the adiabatic descent aloft on the southwestern leeside areas is more significant with warmer temperatures (0.5 K), a larger negative potential vorticity maximum [0.2 potential vorticity units (PVU), 1 PVU = 10−6 K m2 s−1 kg−1], and a more pronounced anticyclonic vortex offshore. The westerly reversed flow off the Kona coast shifts northward.

scholarly journals Validation of the Coupled NCEP Mesoscale Spectral Model and an Advanced Land Surface Model over the Hawaiian Islands. Part I: Summer Trade Wind Conditions and a Heavy Rainfall Event*

2005 ◽  
Vol 20 (6) ◽  
pp. 847-872 ◽  
Author(s):  
Yongxin Zhang ◽  
Yi-Leng Chen ◽  
Song-You Hong ◽  
Hann-Ming Henry Juang ◽  
Kevin Kodama
Keyword(s):  
Land Surface ◽  
Heavy Rainfall ◽  
Hawaiian Islands ◽  
Land Surface Model ◽  
Rainfall Event ◽  
Spectral Model ◽  
Trade Wind ◽  
Heavy Rainfall Event ◽  
Surface Model ◽  
Surface Sites

Abstract Validations of the 10-km operational Regional Spectral Model (RSM) and the coupled Mesoscale Spectral Model (MSM) with an advanced land surface model (LSM) forecasts during a 1-month period from 20 May through 20 June 2002 are performed at three surface sites on the island of Oahu. One heavy rainfall case over the Hawaiian Islands is also simulated using the MSM–LSM. Over land with adequate representation of the terrain, the 1.5-km MSM provides better forecasts of surface variables than the 10-km operational RSM. However, there are still appreciable discrepancies between the MSM simulations and observations. Further improvements are achieved by coupling the MSM with the LSM. In particular, overestimation of the surface wind speed and daytime cold biases experienced by the MSM are largely corrected in the coupled MSM–LSM. Composite analyses of surface variables at three surface sites under different trade wind conditions show that the observed diurnal cycles in 2-m temperature, 2-m dewpoint temperature, and 10-m wind are better forecasted by the MSM–LSM than by the MSM. The observed daytime minima in 2-m dewpoint temperatures during the strong trade wind days at two urban sites are reproduced by the MSM–LSM. The heavy rainfall case studies presented herein indicate that the high-resolution MSM–LSM has better capability in simulating localized rainfall distributions and airflows associated with the heavy rainfall event than the 10-km RSM–LSM. A major model bias is that the MSM–LSM produces excessive rainfall on the windward side of the island of Oahu with no rainfall downstream of the mountain ridges, in contrast to the observed rainfall distribution that shows the maximum rainfall axis occurring slightly downstream of the mountain ridges.

Numerical Simulations of Island-Scale Airflow over Maui and the Maui Vortex under Summer Trade Wind Conditions

2010 ◽  
Vol 138 (7) ◽  
pp. 2706-2736 ◽  
Author(s):  
DaNa L. Carlis ◽  
Yi-Leng Chen ◽  
Vernon R. Morris
Keyword(s):  
Land Surface ◽  
Trade Wind ◽  
Asymmetric Structure ◽  
Return Flow ◽  
Surface Model ◽  
The West ◽  
Downslope Winds ◽  
Cyclonic Vortex ◽  
Trade Wind Inversion ◽  
Low Levels

Abstract The fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) coupled with the Noah land surface model (LSM) is employed to simulate island-scale airflow and circulations over Maui County, Hawaii, under summer trade wind conditions, during July–August 2005. The model forecasts are validated by surface observations with good agreement. In this study, it is shown that a previously known closed circulation over the Central Valley of Maui, or the Maui vortex, represents the northern cyclonic vortex of the dual-counter-rotating vortices in the lee of Haleakala, which extend up to the base of the trade wind inversion with a westerly reversed flow (>2 m s−1). At low levels, the northern cyclonic vortex is more pronounced than the southern anticyclonic vortex. The asymmetric structure of the dual vortices is related to the shape of Haleakala and the flow deflection by the West Maui Mountains. The Maui vortex has a relatively narrow east–west extent in the lowest levels, especially at night, due to the deflected strong northerly/northeasterly winds from the windward foothills of the West Maui Mountains. Unlike the lee vortices off the leeside coast of the island of Hawaii, the Maui vortex and the westerly return flow in low levels are mainly over land and are strongly modulated by the diurnal heating cycle. In addition, the location and horizontal and vertical extent are affected by the trade wind speed and latent heat release. Over the West Maui Mountains, with their height below the trade wind inversion, dual-counter-rotating vortices are present below the 1-km level in the wake, with strong downslope flow on the leeside slopes followed by a hydraulic jump. In the afternoon, downslope winds are weak, with combined westerly return/sea-breeze flow along the leeside coast. Orographic blocking is also evident over eastern Molokai with strong downslope winds, especially at night.

L'apport de la télédétection spatiale à la modélisation des surfaces continentales

2020 ◽  
pp. 052
Author(s):  
Jean-Christophe Calvet ◽  
Jean-Louis Champeaux
Keyword(s):  
Satellite Data ◽  
Land Surface ◽  
Land Surface Model ◽  
Static Model ◽  
Geographic Information ◽  
Surface Model ◽  
Model Parameters

Cet article présente les différentes étapes des développements réalisés au CNRM des années 1990 à nos jours pour spatialiser à diverses échelles les simulations du modèle Isba des surfaces terrestres. Une attention particulière est portée sur l'intégration, dans le modèle, de données satellitaires permettant de caractériser la végétation. Deux façons complémentaires d'introduire de l'information géographique dans Isba sont présentées : cartographie de paramètres statiques et intégration au fil de l'eau dans le modèle de variables observables depuis l'espace. This paper presents successive steps in developments made at CNRM from the 1990s to the present-day in order to spatialize the simulations of the Isba land surface model at various scales. The focus is on the integration in the model of satellite data informative about vegetation. Two complementary ways to integrate geographic information in Isba are presented: mapping of static model parameters and sequential assimilation of variables observable from space.

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