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- Author or Editor: Donald R. Mock x
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Abstract
The originally disseminated ECMWF-FGGE analyses for January and February 1979 are used to study the model performance in the deep tropics. Vertical velocities representing both the normal-mode initialized and uninitialized synoptic-scale flow are compared to directly observed IR radiance from the TIROS-N polar orbiting satellite. This comparison, based on the correlation between cloudiness and vertical motion, is made in the Pacific sector for composites of 1) the intertropical convergence zone, 2) the South Pacific convergence zone, and 3) Northern Hemisphere tropical intrusions. When compared to the uninitialized version, initialization diminishes the magnitude of diagnosed vertical motions in the tropics and Southern Hemisphere by a factor of 2 to 4. For synoptic-scale events away from the equator, especially at upper levels, the patterns of vertical motion are quite similar to each other and correlate moderately well with the radiance observations. Poor correlations in the deep tropics indicate that the original ECMWF-FGGE analyses within 10° of the equator are deficient on the synoptic scale and should be interpreted with caution in this domain.
Abstract
The originally disseminated ECMWF-FGGE analyses for January and February 1979 are used to study the model performance in the deep tropics. Vertical velocities representing both the normal-mode initialized and uninitialized synoptic-scale flow are compared to directly observed IR radiance from the TIROS-N polar orbiting satellite. This comparison, based on the correlation between cloudiness and vertical motion, is made in the Pacific sector for composites of 1) the intertropical convergence zone, 2) the South Pacific convergence zone, and 3) Northern Hemisphere tropical intrusions. When compared to the uninitialized version, initialization diminishes the magnitude of diagnosed vertical motions in the tropics and Southern Hemisphere by a factor of 2 to 4. For synoptic-scale events away from the equator, especially at upper levels, the patterns of vertical motion are quite similar to each other and correlate moderately well with the radiance observations. Poor correlations in the deep tropics indicate that the original ECMWF-FGGE analyses within 10° of the equator are deficient on the synoptic scale and should be interpreted with caution in this domain.
Abstract
Four summers (1967, 1969, 1970, 1971) of rawinsonde data from four western North Pacific island stations (Guam, Midway, Johnston and Wake) were used to form a three-dimensional composite of the subtropical upper-tropospheric cold-core lows commonly found in the mid-Pacific trough. The basic meteorological parameters of wind, height, temperature and humidity were utilized to form an initial composite from the 117 lows identified during the period of study. Satellite mosaics were used to define a composite of horizontal cloud cover. The basic composite was harmonically smoothed and dynamically adjusted to generate a consistent set of derived fields that emphasize the important large-scale characteristics of the phenomenon.
North-south and east-west vertical cross sections through the center of the composite low are used to illustrate the prominent features of the zonal and meridional winds, temperature and height anomalies, relative vorticity, divergence, vertical motion and relative humidity fields. The composite low is mostly confined to the region between 700 and 100 mb. The maximum circulation around the low occurs at 200 mb. The cold anomaly is strongest at 300 mb and lies primarily north of the vortex center. A warm anomaly centered at 125 mb is vertically aligned over the lower-level feature. The cold anomaly extends weakly to the surface. The region to the northwest of the low center is characterized by subsidence and a minimum in the cloudiness of the composite while the region to the southeast is characterized by ascent and a maximum in the cloudiness. Maximum vertical motion occurs near 300 mb.
A calculation of the potential to kinetic energy conversion within the composite low reveals a net direct circulation (positive conversion). The vertical profile of the conversion shows positive contributions from below 200 mb and negative contributions from above. The upper-level disturbance with its associated pattern of low-level convergence to the south and east was found to move at nearly the same speed and direction as the surface easterlies. This lends support to the hypothesis that the upper tropospheric lows can induce a separate surface disturbance. The mechanism involves the amplification of the surface relative vorticity field by a prolonged exposure to the imposed large-scale convergence.
Abstract
Four summers (1967, 1969, 1970, 1971) of rawinsonde data from four western North Pacific island stations (Guam, Midway, Johnston and Wake) were used to form a three-dimensional composite of the subtropical upper-tropospheric cold-core lows commonly found in the mid-Pacific trough. The basic meteorological parameters of wind, height, temperature and humidity were utilized to form an initial composite from the 117 lows identified during the period of study. Satellite mosaics were used to define a composite of horizontal cloud cover. The basic composite was harmonically smoothed and dynamically adjusted to generate a consistent set of derived fields that emphasize the important large-scale characteristics of the phenomenon.
North-south and east-west vertical cross sections through the center of the composite low are used to illustrate the prominent features of the zonal and meridional winds, temperature and height anomalies, relative vorticity, divergence, vertical motion and relative humidity fields. The composite low is mostly confined to the region between 700 and 100 mb. The maximum circulation around the low occurs at 200 mb. The cold anomaly is strongest at 300 mb and lies primarily north of the vortex center. A warm anomaly centered at 125 mb is vertically aligned over the lower-level feature. The cold anomaly extends weakly to the surface. The region to the northwest of the low center is characterized by subsidence and a minimum in the cloudiness of the composite while the region to the southeast is characterized by ascent and a maximum in the cloudiness. Maximum vertical motion occurs near 300 mb.
A calculation of the potential to kinetic energy conversion within the composite low reveals a net direct circulation (positive conversion). The vertical profile of the conversion shows positive contributions from below 200 mb and negative contributions from above. The upper-level disturbance with its associated pattern of low-level convergence to the south and east was found to move at nearly the same speed and direction as the surface easterlies. This lends support to the hypothesis that the upper tropospheric lows can induce a separate surface disturbance. The mechanism involves the amplification of the surface relative vorticity field by a prolonged exposure to the imposed large-scale convergence.
Abstract
Heat and moisture budgets are used to compute net condensation rates in the GATE B-scale network for four hours of the day: 0000, 0600, 1200 and 1800 GMT. Budgets are presented for all phases combined, for selected periods of enhanced convection and for selected periods of suppressed convection. Computations are based on fitted values of the meteorological sounding data for the center of the B-scale ship array, on surface heat flux and evaporation measurements for seven ships in the array and on Cox and Griffith's (1979) radiation measurements for Phase III. Results are also presented for the diurnal variation of the basic variables.
Main findings are as follows:
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1) Temperature variations are small, of the order of a few tenths of a degree, with a daytime maximum and nighttime minimum. There is evidence of possible radiation error above 400 mb where the amplitude is largest.
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2) The atmosphere appears to be relatively dry during the day, when convection is most active, and relatively moist at night. It is suggested that this behavior may be caused by instrumental error.
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3) The divergence and vertical velocity undergo characteristic cycles that were repeated in all three phases. It is hypothesized from their behavior that the convection evolves in three distinct stages: a stage of shallow convection during the early night, a stage of vigorously growing, primarily moderate-depth convection in the late night and morning and a stage of predominantly deep convection in the afternoon.
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4) The vertical advection terms dominated both budgets. Variations of heat and moisture storage and of radiation were also important. Surface evaporation and sensible heat flux were essentially constant throughout the day.
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5) Rainfall diagnosed from the heat budget was less than the observed precipitation and rainfall diagnosed from the moisture budget was greater than the observed precipitation in all three phases.
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6) Maximum diagnosed condensation preceded maximum observed precipitation by ∼6 h. Differences between condensation and precipitation rates are attributed in part to storage of condensed water, though errors of measurement undoubtedly contributed to them as well.
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7) The diurnal cycles of precipitation and low-level vertical motion were much larger in the disturbed (trough) region of easterly waves than in the suppressed (ridge) region. During highly suppressed periods the precipitation was uniformly distributed throughout the day while the vertical motion still appeared to show a variation.
Abstract
Heat and moisture budgets are used to compute net condensation rates in the GATE B-scale network for four hours of the day: 0000, 0600, 1200 and 1800 GMT. Budgets are presented for all phases combined, for selected periods of enhanced convection and for selected periods of suppressed convection. Computations are based on fitted values of the meteorological sounding data for the center of the B-scale ship array, on surface heat flux and evaporation measurements for seven ships in the array and on Cox and Griffith's (1979) radiation measurements for Phase III. Results are also presented for the diurnal variation of the basic variables.
Main findings are as follows:
-
1) Temperature variations are small, of the order of a few tenths of a degree, with a daytime maximum and nighttime minimum. There is evidence of possible radiation error above 400 mb where the amplitude is largest.
-
2) The atmosphere appears to be relatively dry during the day, when convection is most active, and relatively moist at night. It is suggested that this behavior may be caused by instrumental error.
-
3) The divergence and vertical velocity undergo characteristic cycles that were repeated in all three phases. It is hypothesized from their behavior that the convection evolves in three distinct stages: a stage of shallow convection during the early night, a stage of vigorously growing, primarily moderate-depth convection in the late night and morning and a stage of predominantly deep convection in the afternoon.
-
4) The vertical advection terms dominated both budgets. Variations of heat and moisture storage and of radiation were also important. Surface evaporation and sensible heat flux were essentially constant throughout the day.
-
5) Rainfall diagnosed from the heat budget was less than the observed precipitation and rainfall diagnosed from the moisture budget was greater than the observed precipitation in all three phases.
-
6) Maximum diagnosed condensation preceded maximum observed precipitation by ∼6 h. Differences between condensation and precipitation rates are attributed in part to storage of condensed water, though errors of measurement undoubtedly contributed to them as well.
-
7) The diurnal cycles of precipitation and low-level vertical motion were much larger in the disturbed (trough) region of easterly waves than in the suppressed (ridge) region. During highly suppressed periods the precipitation was uniformly distributed throughout the day while the vertical motion still appeared to show a variation.
