Mean Monthly Maps Research Articles

The China Coastal Front from Himawari-8 AHI SST Data—Part 1: East China Sea

High-resolution (2 km) high-frequency (hourly) SST data from 2015–2020 provided by the Advanced Himawari Imager (AHI) onboard the Japanese Himawari-8 geostationary satellite positioned over 140.7°E were used to study spatial and temporal variability of the China Coastal Front (CCF) in the East China Sea. This dataset was processed with the Belkin and O’Reilly algorithm to generate long-term mean monthly maps of the SST gradient magnitude (GM) and frontal frequency (FF). The horizontal structure of the SST field in the vicinity of the CCF was also investigated from the cross-frontal distributions of SST along eight parallels between 31°N and 24°N. The monthly mean distributions of SST along these 8 parallels were used to determine inshore and offshore boundaries of the CCF and to calculate the CCF strength defined as the total cross-frontal step (range) dSST calculated as the difference between offshore and inshore SST. The CCF emerges in November, fully develops in December, and peaks in strength in January–February. The front’s fragmentation and shrinking/weakening begins in February and March, respectively. In winter (December–February), the front’s strength dSST exceeds 5 °C offshore the Zhejiang-Fujian coast and could be as high as 7.5 °C when nearshore waters cool down to 7 °C. In winter, the front’s strength decreases downstream between 31°N and 24°N. The CCF changes its physical nature as the seasons progress. In winter, the CCF is a water mass front between the cold and fresh water coming from the north and the warm and salty water coming from the south. In summer, the CCF becomes a coastal upwelling front maintained largely by southerly winds. In winter, the CCF’s cross-frontal structure in the SST field is ramp-shaped, with SST increasing monotonously in the offshore direction. In summer, the CCF’s cross-frontal structure in the SST field is V-shaped or U-shaped, featuring a minimum SST formed by cold upwelled water at some distance from the shore. Thus, the summer SST structure effectively consists of two parallel fronts, an inshore one and an offshore one, with a minimum SST in between. Across the inshore/offshore front, the SST decreases/increases in the offshore direction.

Comparison of geostatistical approaches to spatially interpolate month‐year rainfall for the Hawaiian Islands

ABSTRACTThe Hawaiian Islands have one of the most spatially diverse rainfall patterns on earth. Knowledge of these patterns is critical for a variety of resource management issues and, until now, only long‐term mean monthly and annual rainfall maps have been available for Hawai‘i. In this study, month‐year rainfall maps from January 1920 to December 2012 were developed for the major Hawaiian Islands. The maps were produced using climatologically aided interpolation (CAI), where the station anomalies were interpolated first, and then combined with the mean maps. A geostatistical method comparison was performed to choose the best interpolation method. The comparison focuses on three kriging algorithms: ordinary kriging (OK), ordinary cokriging (OCK), and kriging with an external drift (KED). Two covariates, elevation and mean rainfall, were tested with OCK and KED. The combinations of methods and covariates were compared using cross‐validation statistics, where OK produced the lowest error statistics. Station anomalies for each month were interpolated using OK and combined with the mean monthly maps to produce the final month‐year rainfall maps.

The Southwest Branch of the North American Monsoon during Summer 1979

Abstract The physical characteristics of the southwest branch of the North American monsoon system during the summer of 1979 are studied with the FGGE dataset. The combined features such as the low pressure trough over northwestern Mexico, the penetration of the easterly flow from the Atlantic Ocean, and the intensification. of the anticyclonic gyre of the South Pacific, are responsible, during the summer, for a well established cross-equatorial surface air flow along the eastern tropical Pacific Ocean and western Mexico. Mean monthly maps of vertically integrated water-vapor flux show the development of a low-level jet favoring the penetration, into western Mexico, of a cross-equatorial moist flow which originates over the southern Pacific. It is shown that the South Pacific anticyclone gyre is an important feature which brings moist air along western Mexico. The mean monthly evolution of the net water-vapor flux divergence suggests a strong association with the precipitation pattern observed over Mexico.

World ocean mean monthly waves, swell, and surface winds for July through October 1978 from SEASAT radar altimeter data

Abstract Data acquired by the SEASAT radar altimeter during the satellite's three‐month lifetime are used to obtain mean monthly maps of significant wave height, minimum swell, and surface wind speed for the world oceans. The SEASAT lifetime 26 June to 10 October 1978, corresponds to the Arctic summer and Antarctic winter. Thus, the highest sea states as derived from the radar altimeter data occur in the high latitudes of the Southern Ocean, reaching the mean monthly extreme magnitudes of 6‐m significant wave height, 5‐m minimum swell amplitude, and 12 m/s surface wind speed. Several features of the wave and wind fields agree with conventional descriptions. For example, the principal zonal wind regimes of the westerlies and trade winds and the doldrums and monsoon region are clearly evident in the monthly averages. Significant wave height and swell, whose mean fields always appear to be smoother than the mean wind speed fields, exhibit minima near the doldrums and steady increases southward and northward ...

Southern ocean mean monthly waves and surface winds for winter 1978 by Seasat radar altimeter

Data acquired by the SEASAT radar altimeter during the 3 month satellite lifetime are analyzed in a study of the sea state of the southern hemisphere oceans. The lifetime of the SEASAT satellite, July 7 to October 10, 1978, corresponds to the Antarctic winter. Mean monthly maps of wind speed, significant wave height, and swell have been generated from the altimeter measurements along the satellite tracks. These maps delineate spatial and temporal differences of these parameters in the Atlantic, Indian, and Pacific oceans. Several features of the Southern Ocean wind and wave fields agree with conventional descriptions. For example, the principle zonal wind regimes established by the Southeast Trades and Westerlies are clearly evident in the monthly averages. Significant wave height and swell also exhibit minima near the Doldrums at low latitudes with steady increases southward to the latitudes of the Westerlies. However, superimposed on these general patterns is significant variability with horizontal scales as small as 1000 km. The maps also document a gradual migration of the region of absolute maximum wind and wave from the Atlantic eastward to the Indian Ocean and finally into the Pacific.

Evidence for a Quasi-Biennial Variation in Eccentricity of the North Polar Vortex

Abstract The centroid of the north polar vortex has been determined from 300 mb mean-monthly maps for the 10-year period 1963–72. There is a significant correlation of 0.79 between the 12-month running average distance of the centroid from the North Pole and the 50 mb zonal wind at Balboa, Canal Zone; i.e., the eccentricity appears to be greater at the time of quasi-biennial cast wind minimum

The distribution of mean monthly precipitable water vapor and annual precipitation efficiency in Nigeria

Precipitable water vapor was calculated for Nigeria using a combination of surface and upper air data and mean monthly maps have been drawn. Annual maps of precipitable water vapor and precipitation efficiency have also been included.