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Joseph S. Scire
and
Joseph Chang

Abstract

A comprehensive air quality and meteorological monitoring project entitled the South-Central Coast Cooperative Aerometric Monitoring Program (SCCCAMP 1985) was conducted in the Santa Barbara Channel and adjacent areas from Point Sal to Point Dume during a five-week period in September–October 1985. As part of a larger study to analyze the SCCCAMP 1985 observations and related databases, an analysis has been conducted of a six-year historical ozone and meteorological database.

The objectives of the historical data analysis study were to 1) characterize meteorological and ozone concentration patterns during a six-year historical period (1979–1984), 2) identify relationships between meteorological variables and high ozone concentrations in the SCCCAMP region, and 3) compare the meteorological conditions and ozone concentrations observed during the SCCCAMP 1985 study with those during the same periods in the historical database in order to assess the representativeness of the SCCCAMP 1985 study period as a whole and individual high ozone events within the period.

The analysis indicated that high ozone concentrations in Santa Barbara County were associated with two conditions occurring simultaneously: 1) subsidence and limited mixing conditions, and 2) moderate easterly or southerly geostrophic flow. Although the actual flow fields and mixing conditions in the region are complex and variable, the 850-mb temperature and surface-pressure parameters were found to be useful, robust indicators of high ozone conditions in Santa Barbara. The seasonal distribution of high ozone events in Santa Barbara County, which peaks in September with a secondary peak in June, was found to be strongly related to the seasonal frequency of occurrence of favorable values of these meteorological variables. In contrast, the peak Ventura County ozone concentrations did not show the same sensitivity to surface pressure parameters, and the seasonal frequency of high ozone events, which peak in July, corresponds closely to that of the 850-mb temperature.

The SCCCAMP 1985 period was unusual in terms of its low frequency of occurrence of meteorological conditions associated with high ozone events in the region. As a result the observed average ozone concentrations were below historical values. However, several high ozone events did occur during the SCCCAMP 1985 study. The meteorological conditions during these individual events were found to be consistent with those typical of historical high ozone events.

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Yonghong Li
and
Julius S. Chang

Abstract

The flux-form advection scheme of Bott is modified for the spherical coordinates, combined with the expanded-polar-zone (EPZ) technique to improve the overall performance of the advection calculations. With the EPZ technique, this Eulerian scheme has comparable efficiency as semi-Lagrangian methods for advection of nonreactive tracers on a sphere but with somewhat better overall numerical accuracy. The conservation of global tracer mass and the, positive definiteness of the algorithm are achieved to machine precision. For the test problem of solid body rotations on a sphere, this scheme shows small numerical diffusion, almost undetectable phase errors, and very little artificial deformation of the test shape even for cross-polar transport. In comparison with some semi-Lagrangian schemes and other high-order Eulerian methods, it shows very competitive performance. Numerical tests also indicate that, without any modifications, it performs just as well on slightly nonuniform Gaussian grid as on uniform grid. For the vertical advection, a fourth-order and two second-order versions of this scheme formulated on a nonuniform grid system have also been derived. The performance of these versions is tested with a nonuniform sigma grid system by using ideal one-dimensional test problems. This accurate numerical scheme is recommended for models where resolving the sharp vertical gradients of atmospheric trace species such as water vapor is important.

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Tsing-Chang Chen
,
Ming-Cheng Yen
,
Jenq-Dar Tsay
,
Chi-Chang Liao
, and
Eugene S. Takle

Abstract

Environmental conditions for the roughly three million people living in the Taipei basin of Taiwan are greatly affected by the land–sea breeze and afternoon thunderstorm activities. A new perspective on the land–sea breeze life cycle and how it is affected by afternoon thunderstorm activity in the Taipei basin during the dry season is provided. During the summer monsoon break–revival phase, about 75% of rainfall in the Taipei basin is produced by afternoon thunderstorms triggered by sea-breeze interactions with the mountains to the south of this basin. Because the basic characteristics of the land–sea breeze and the changes it undergoes through the influence of afternoon thunderstorms have not been comprehensively analyzed/documented, a mini–field experiment was conducted during the summers of 2004 and 2005 to explore these aspects of the land–sea breeze in this basin. Thunderstorm rainfall is found to change not only the basin’s land–sea-breeze life cycle, but also its ventilation mechanism. On the nonthunderstorm day, the sea breeze supplies the open-sea fresh air for about 8 h during the daytime, but the land breeze persists on the thunderstorm day from afternoon to the next morning, acting to sweep polluted urban air out of the basin.

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Tsing-Chang Chen
,
Jenq-Dar Tsay
, and
Eugene S. Takle

Abstract

The Taipei basin, located in northern Taiwan, is formed at the intersection of the Tanshui River valley (~30 km) and the Keelung River valley (~60 km). Summer is the dry season in northern Taiwan, but the maximum rainfall in the Taipei basin occurs during 15 June–31 August. The majority of summer rainfall in this basin is produced by afternoon thunderstorms. Thus, the water supply, air/land traffic, and pollution for this basin can be profoundly affected by interannual variations of thunderstorm days and rainfall. Because the mechanism for these interannual variations is still unknown, a systematic analysis is made of thunderstorm days and rainfall for the past two decades (1993–2013). These two variables are found to correlate opposite interannual variations of sea surface temperature anomalies over the National Oceanic and Atmospheric Administration Niño-3.4 region. Occurrence days for afternoon thunderstorms and rainfall amounts in the Taipei basin double during the cold El Niño–Southern Oscillation (ENSO) phase relative to the warm phase. During the latter phase, a stronger cold/drier monsoon southwesterly flow caused by the Pacific–Japan Oscillation weakens the thunderstorm activity in the Taipei basin through the land–sea breeze. In contrast, the opposite condition occurs during the cold ENSO phase. The water vapor flux over the East/Southeast Asian monsoon region converges more toward Taiwan to maintain rainfall over the Taipei basin during the cold ENSO phase than during the warm ENSO phase.

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S. Chang
,
D. Hahn
,
C-H. Yang
,
D. Norquist
, and
M. Ek

Abstract

An updated complete and comprehensive description of the land surface parameterization scheme in the Coupled Atmosphere–Plant–Soil (CAPS) model is presented. The CAPS model has been in development at Oregon State University and Phillips Laboratory since 1981. The CAPS model was originally designed for a global atmospheric model, but it has also been used as a stand-alone model for a variety of applications. The land surface scheme in the CAPS model is one of the two dozen schemes that participated in the Project for Intercomparison of Land Surface Parameterization Schemes (PILPS). Some unique features of the CAPS scheme are given in detail. A comprehensive dataset of one year (1987), including atmospheric forcing data and validation data from Cabauw, has been provided for PILPS by the Royal Netherlands Meteorological Institute. Using the Cabauw data, a validation study for the CAPS scheme has been carried out. The scheme’s self-consistencies in terms of surface energy balance and water budget are discussed. Finally, the results of this validation study with emphasis on the performance of surface momentum and heat fluxes are presented.

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Long S. Chiu
,
Alfred T. C. Chang
, and
John Janowiak

Abstract

Three years of monthly rain rates over 5° × 5° latitude–longitude boxes have been calculated for oceanic regions 50°N–50°S from measurements taken by the Special Sensor Microwave/Imager on board the Defense Meteorological Satellite Program satellites using the technique developed by Wilheit et al. The annual and seasonal zonal-mean rain rates are larger than Jaeger's climatological estimates but are smaller than those estimated from the GOES precipitation index (GPI) for the same period. Regional comparison with the GPI showed that these rain rates are smaller in the north Indian Ocean and in the southern extratropics where the GPI is known to overestimate. The differences are also dominated by a jump at 170°W in the GPI rain rates across the mid Pacific Ocean. This jump is attributed to the fusion of different satellite measurements in producing the GPI.

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J. C. Hubbert
,
S. M. Ellis
,
W.-Y. Chang
,
S. Rutledge
, and
M. Dixon

Abstract

Data collected by the National Center for Atmospheric Research S-band polarimetric radar (S-Pol) during the Terrain-Influenced Monsoon Rainfall Experiment (TiMREX) in Taiwan are analyzed and used to infer storm microphysics in the ice phase of convective storms. Both simultaneous horizontal (H) and vertical (V) (SHV) transmit polarization data and fast-alternating H and V (FHV) transmit polarization data are used in the analysis. The SHV Z dr (differential reflectivity) data show radial stripes of biased data in the ice phase that are likely caused by aligned and canted ice crystals. Similar radial streaks in the linear depolarization ratio (LDR) are presented that are also biased by the same mechanism. Dual-Doppler synthesis and sounding data characterize the storm environment and support the inferences concerning the ice particle types. Small convective cells were observed to have both large positive and large negative K dp (specific differential phase) values. Negative K dp regions suggest that ice crystals are vertically aligned by electric fields. Since high |K dp| values of 0.8° km−1 in both negative and positive K dp regions in the ice phase are accompanied by Z dr values close to 0 dB, it is inferred that there are two types of ice crystals present: 1) smaller aligned ice crystals that cause the K dp signatures and 2) larger aggregates or graupel that cause the Z dr signatures. The inferences are supported with simulated ice particle scattering calculations. A radar scattering model is used to explain the anomalous radial streaks in SHV and LDR.

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J. C. Hubbert
,
S. M. Ellis
,
W.-Y. Chang
, and
Y.-C. Liou

Abstract

In this paper, experimental X-band polarimetric radar data from simultaneous transmission of horizontal (H) and vertical (V) polarizations (SHV) are shown, modeled, and microphysically interpreted. Both range–height indicator data and vertical-pointing X-band data from the Taiwan Experimental Atmospheric Mobile-Radar (TEAM-R) are presented. Some of the given X-band data are biased, which is very likely caused by cross coupling of the H and V transmitted waves as a result of aligned, canted ice crystals. Modeled SHV data are used to explain the observed polarimetric signatures. Coincident data from the National Center for Atmospheric Research S-band polarimetric radar (S-Pol) are presented to augment and support the X-band polarimetric observations and interpretations. The polarimetric S-Pol data are obtained via fast-alternating transmission of horizontal and vertical polarizations (FHV), and thus the S-band data are not contaminated by the cross coupling (except the linear depolarization ratio LDR) observed in the X-band data. The radar data reveal that there are regions in the ice phase where electric fields are apparently aligning ice crystals near vertically and thus causing negative specific differential phase K dp. The vertical-pointing data also indicate the presence of preferentially aligned ice crystals that cause differential reflectivity Z dr and differential phase ϕ dp to be strong functions of azimuth angle.

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T. T. Wilheit
,
A. T. C. Chang
,
M. S. V. Rao
,
E. B. Rodgers
, and
J. S. Theon

Abstract

A theoretical model for calculating microwave radiative transfer in raining atmospheres is developed. These calculations are compared with microwave brightness temperatures at a wavelength of 1.55 cm measured by the Electrically Scanning Microwave Radiometer (ESMR) on the Nimbus 5 satellite and rain rates derived from WSR-57 meteorological radar measurements. A specially designed ground-based verification experiment was also performed, wherein upward viewing microwave brightness temperature measurements at wavelengths of 1.55 and 0.81 cm were compared with directly measured rain rates. It is shown that over ocean areas, brightness temperature measurements from ESMR may be interpreted in terms of rain rate with about an accuracy of a factor of 2 over the range 1–25 mm h−1 rain rate.

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T. T. Wilheit
,
A. T. C. Chang
,
J. L. King
,
E. B. Rodgers
,
R. A. Nieman
,
B. M. Krupp
,
A. S. Milman
,
J. S. Stratigos
, and
H. Siddalingaiah

Abstract

Observations of rain cells in the remains of a decaying tropical storm were made by Airborne Microwave Radiometers at 19.35 and 92 GHz and three frequencies near 183 GHz. Extremely low brightness temperatures, as low as 140 K, were noted in the 92 and 183 GHz observations. These can be accounted for by the ice often associated with raindrop formation. Further, the 183 GHz observations can be interpreted in terms of the height of the ice. The brightness temperatures observed suggest the presence of precipitationsized ice as high as 9 km or more.

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