Numerical Simulations of the Island-Induced Circulations over the Island of Hawaii during HaRP

2005 ◽  
Vol 133 (12) ◽  
pp. 3693-3713 ◽  
Author(s):  
Yang Yang ◽  
Yi-Leng Chen ◽  
Francis M. Fujioka
Keyword(s):  
Land Surface ◽  
Diurnal Variations ◽  
Windward Side ◽  
Trade Wind ◽  
Wind Flow ◽  
State University ◽  
Thermal Contrast ◽  
Sea Breezes ◽  
Flow Deceleration ◽  
Trade Wind Inversion

Abstract The fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5)/land surface model (LSM) is used to simulate the diurnal island-scale circulations over the island of Hawaii during the Hawaiian Rainband Project (HaRP, 11 July–24 August 1990). The model is initialized with the NCEP–NCAR reanalysis data. The diurnal variations of the land–sea thermal contrast at the land surface and the planetary boundary layer at Hilo, Hawaii, are well simulated. The main discrepancy occurs on the leeside areas of mountains or ridges below the trade wind inversion (2 km), where the simulated afternoon land–sea thermal contrast at the surface is 1°–3°C lower than observed mainly due to the misrepresentation of lava rocks by the bare ground category in the U.S. Geological Survey (USGS) data and stronger than observed simulated sea breezes bringing in relatively cool maritime air. The flow deceleration and splitting of the incoming trade wind flow and the evolution of the diurnal circulation cells on the windward side, the thermally driven diurnal winds, and the wake circulations on the lee side are well simulated. The simulated diurnal variations in rainfall are also in good agreement with observations. However, the simulated winds in areas well exposed to the trade wind flow are weaker (1–3 m s−1) than observed mainly due to the underestimation of trade wind flow in the NCEP–NCAR reanalysis. The simulated rainfall over windward lowlands at night is underestimated and the maximum rainfall axis shifts farther toward the coast as compared with observations, due to an underestimation of orographic lifting aloft and a relatively large horizontal extent of the simulated katabatic flow because of the weaker- than-observed trade wind flow in the initial conditions. In the afternoon hours on the windward side, the strongest winds (anabatic/sea breeze and trade wind flow) are simulated in low levels over land in response to the surface heating, with a westerly wind deviation beneath the mean trade wind inversion (2 km) and sinking motion over the adjacent oceans. The simulated low-level flow deceleration of the incoming trade wind flow is most significant in the early morning as a combination of island blocking and nocturnal cooling over land. At that time, the simulated upward motion representing the rising branch of the thermally direct circulation extends more than 40 km offshore. Sensitivity tests show that with better surface conditions in the model coupled with the Oregon State University (OSU) LSM, the simulated thermal forcing over land is improved. The improvements in simulated ground temperature, land–sea thermal contrast at the land surface, and mixing ratio lead to better simulation of the strength of land/sea breezes over the island.

Characteristics of Summer Trade Wind Rainfall over Oahu

2010 ◽  
Vol 25 (6) ◽  
pp. 1797-1815 ◽  
Author(s):  
Treena Marie Hartley ◽  
Yi-Leng Chen
Keyword(s):  
Land Surface ◽  
Early Morning ◽  
Windward Side ◽  
Trade Wind ◽  
Sea Breezes ◽  
Orographic Rainfall ◽  
Flow Deceleration ◽  
Study Characteristics ◽  
Cloud Development ◽  
Variable Wind

Abstract In this study, characteristics of summer trade wind rainfall over Oahu, Hawaii, are analyzed. In the early morning before sunrise, flow deceleration on the windward coastal area is the greatest when the island land surface is the coldest. Furthermore, relatively calm winds are found over central Oahu between the Ko’olau Mountains and the Waianae Mountains, with weak westerly katabatic winds on the windward side of the Waianae Mountains. Most windward stations have an early morning rainfall maximum with a secondary rainfall maximum in the early evening. Morning (afternoon) land (sea) breezes dominate under variable winds, and are more pronounced over leeward Oahu. Precipitation on the western leeside coast has a slight peak in the afternoon due to an increase of cloud development from the afternoon sea breezes. Daily orographic rainfall over Oahu is greater under the strong trade wind regime, and less under weak trade wind and variable-wind flow regimes. However, the maximum correlation between daily trade wind rainfall and trade wind speed is <0.3. Days with high rainfall generally occur under strong trades, but not all strong trade wind days produce significant rainfall. With its relatively low terrain height compared to lifted condensation level (LCL) and relatively small size, orographic lifting alone is inadequate to initiate precipitation through warm rain processes. The existence of trade wind cumuli upstream is necessary. In addition, a deeper moist layer and higher moisture content upstream are two conditions that are favorable for higher orographic precipitation over Oahu under undisturbed summertime trade wind weather.

Numerical Simulations of Island Effects on Airflow and Weather during the Summer over the Island of Oahu

2010 ◽  
Vol 138 (6) ◽  
pp. 2253-2280 ◽  
Author(s):  
Hiep Van Nguyen ◽  
Yi-Leng Chen ◽  
Francis Fujioka
Keyword(s):  
Land Surface ◽  
Mesoscale Model ◽  
Ground Cover ◽  
Horizontal Distribution ◽  
Diurnal Variations ◽  
Windward Side ◽  
Trade Wind ◽  
Surface Model ◽  
Downslope Winds ◽  
Early Afternoon

Abstract The high-resolution (1.5 km) nonhydrostatic fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) and an advanced land surface model (LSM) are used to study the island-induced airflow and weather for the island of Oahu, Hawaii, under summer trade wind conditions. Despite Oahu’s relatively small area (1536 km2), there are considerable spatial variations in horizontal distribution of thermodynamic fields related to terrain, airflow, rain, cloud, and ground cover. The largest diurnal variations in temperature and moisture occur in the lee sides of mountains, especially along the western leeside coast. The island-scale surface airflow is also significantly affected by terrain and land surface forcing. The downslope winds above the leeside slopes of both the Ko’olau and Waianae Mountains are simulated with significant diurnal variations with the strongest downslope winds just before sunrise. The timing of diurnal rainfall maxima over the Ko’olau Mountains is closely related to vertical motions. The early morning rainfall maximum on the windward side is caused by anomalous rising motion due to significant flow deceleration when the land surface is the coolest. The evening rainfall maximum after sunset is related to anomalous orographic lifting due to stronger winds aloft. In the early afternoon, winds aloft are relatively weak with a relatively high level of free convection (LFC) because of vertical mixing. As a result, the rainfall over the Ko’olau Mountains exhibits an afternoon minimum. The westerly reversed flow off the western leeside coast in the afternoon is mainly thermally driven and related to land surface heating superimposed by latent heat release of persistent orographic precipitation over the Ko’olau Mountains. Rainfall along the western leeside slopes has a late afternoon maximum due to the development of the onshore/upslope flow.

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 Effects of Trade Wind Strength on Airflow and Cloudiness over O‘ahu

2021 ◽  
Author(s):  
Feng Hsiao ◽  
Yi-Leng Chen ◽  
Hiep Van Nguyen ◽  
David Eugene Hitzl ◽  
Robert Ballard
Keyword(s):  
Sea Breeze ◽  
Windward Side ◽  
Trade Wind ◽  
Return Flow ◽  
Western Coast ◽  
Trade Winds ◽  
Flow Deceleration ◽  
Orographic Clouds ◽  
Island Wake ◽  
Orographic Cloud

AbstractSatellite observations and high-resolution modeling during July–August 2013 are used to study the effects of trade wind strength on island wake circulations and cloudiness over O‘ahu, Hawai‘i. O‘ahu is composed of two northwest–southeast orientated mountain ranges: the Wai‘anae Range (~1227 m) along the western leeside coast and the Ko‘olau Range (~944 m) along the eastern windward coast. At night, the flow deceleration of the incoming northeasterly trade winds on the eastern windward side is more significant when trades are stronger.In the afternoon hours, effective albedo and simulated cloud water are greater over the Ko‘olau Range when trades are stronger, and clouds are advected downstream by the trade winds aloft. Over the Wai‘anae Range, orographic clouds are more significant when trades are weaker due to less moisture removal by orographic precipitation over the Ko‘olau Range and the development of both upslope flow on the eastern slope and upslope/sea-breeze flow along the western coast, the latter of which brings in warm, moist air from the ocean. When trades are weaker, cloudiness off the western leeside coast is more extensive and originates from orographic cloud development over the Wai‘anae Range, which drifts downstream due to a combination of trade winds and the easterly return flow aloft. The latter is associated with the low-level sea-breeze/upslope flow.

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.

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 Numerical Simulations of Sea-Breeze Circulations over Northwest Hawaii*

2005 ◽  
Vol 20 (6) ◽  
pp. 827-846 ◽  
Author(s):  
Yongxin Zhang ◽  
Yi-Leng Chen ◽  
Thomas A. Schroeder ◽  
Kevin Kodama
Keyword(s):  
Land Surface ◽  
Onset Time ◽  
Surface Air Temperature ◽  
Sea Breeze ◽  
Horizontal Resolution ◽  
Trade Wind ◽  
Surface Model ◽  
Time Duration ◽  
Sea Breezes ◽  
Model Simulations

Abstract Sea-breeze cases during 23–28 June 1978 over northwest Hawaii are simulated using the National Centers for Environmental Prediction (NCEP) Mesoscale Spectral Model (MSM) coupled with an advanced Land Surface Model (LSM) with 3-km horizontal resolution. Subjective analyses show that except for 27 June, the MSM–LSM-predicted onset time, duration, and vertical extent of the sea breezes agree well with observations. The largest mean absolute errors for surface air temperature occur at the coastal stations under strong trade wind conditions (e.g., 23 and 27 June). The model-simulated rainfall distribution in association with sea-breeze fronts is consistent with observations. Sensitivity tests demonstrate the modulation of sea-breeze behavior by surface properties. High-resolution (1 km) MSM–LSM simulations for 23 and 27 June show improvements over the 3-km MSM–LSM in reproducing the observed sea breezes through a better representation of local terrain and a better simulation of orographically enhanced trades channeling through the Waimea Saddle. Deficiencies noted in the model simulations include 1) sea-breeze speeds are more than 2–3 m s−1 weaker than observations, and 2) horizontal penetration of sea breezes is generally overestimated. These deficiencies in the model simulations are primarily related to two factors: one is the underestimation of the trade wind speeds in the initialization from the NCEP–NCAR reanalysis data that is favoring the farther penetration of the sea breezes, and the other is the uncertainties in the thermal properties of the lava rocks that affect the surface temperature and the sea-breeze speed.

Climatology of the Trade-Wind Inversion in the Caribbean

1958 ◽  
Vol 39 (8) ◽  
pp. 410-420 ◽  
Author(s):  
Murray Gutnick
Keyword(s):  
Seasonal Variation ◽  
Diurnal Variation ◽  
Diurnal Variations ◽  
Trade Wind ◽  
Moisture Budget ◽  
Base Strength ◽  
Trade Wind Inversion ◽  
The Caribbean

Three years of twice-daily raobs for the midseason months at six stations on the Caribbean were analyzed for evidence of the trade-wind inversion. The seasonal, spatial, or diurnal variation of the various parameters which constitute the inversion regime (frequency, height of the base, strength, thickness, and moisture budget) is discussed. It was found that most of the parameters showed a distinct seasonal variation but little or no spatial or diurnal variations.

Dynamical Adjustment of the Trade Wind Inversion Layer

1995 ◽  
Vol 52 (16) ◽  
pp. 2941-2952 ◽  
Author(s):  
Wayne H. Schubert ◽  
Paul E. Ciesielski ◽  
Chungu Lu ◽  
Richard H. Johnson
Keyword(s):  
Inversion Layer ◽  
Trade Wind ◽  
Trade Wind Inversion
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