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Mo, Kingtse C.

Publications and source records attributed to Mo, Kingtse C..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

The Low-Frequency Variability of the Tropical Atlantic Ocean

Upper ocean temperature variability in the tropical Atlantic is examined from the Comprehensive Ocean Atmosphere Data Set (COADS) as well as from an ocean model simulation forced by COADS anomalies appended to a monthly climatology. Our findings are as follows: Only the sea surface temperatures (SST) in the northern tropics are driven by heat fluxes, while the southern tropical variability arises from wind driven ocean circulation changes. The subsurface temperatures in the northern and southern tropics are found to have a strong linkage to buoyancy forcing changes in the northern North Atlantic. Evidence for Kelvin-like boundary wave propagation from the high latitudes is presented from the model simulation. This extratropical influence is associated with wintertime North Atlantic Oscillation (NAO) forcing and manifests itself in the northern and southern tropical temperature anomalies of the same sign at depth of 100-200 meters as result of a Rossby wave propagation away from the eastern boundary in the wake of the boundary wave passage. The most apparent association of the southern tropical sea surface temperature anomalies (STA) arises with the anomalous cross-equatorial winds which can be related to both NAO and the remote influence from the Pacific equatorial region. These teleconnections are seasonal so that the NAO impact on the tropical SST is the largest it mid-winter but in spring and early summer the Pacific remote influence competes with NAO. However, NAO appears to have a more substantial role than the Pacific influence at low frequencies during the last 50 years. The dynamic origin of STA is indirectly confirmed from the SST-heat flux relationship using ocean model experiments which remove either anomalous wind stress forcing or atmospheric forcing anomalies contributing to heat exchange.

Haekkinen, Sirpa↗
NASA NTRS1997

Interannual Fluctuations in Atmospheric Angular Momentum Simulated by the National Centers for Environmental Prediction Medium Range Forecast Model

An earlier study established the existence of globally coherent interannual fluctuations in atmospheric angular momentum (AAM), associated with the El Nino-Southern Oscillation (ENSO) cycle. In this paper, we pursue the origin and the structure of these fluctuations using an ensemble of experiments generated by the National Centers for Environmental Prediction, medium range forecast model version 9. In the control experiments, where the observed sea surface temperatures (SSTs) were used as the lower boundary conditions, the model captures the characteristic V-like structure in time-latitude plots of zonally averaged AAM, while experiments with climatological SSTs and those with either perpetual warm or cold ENSO conditions superimposed on the climatological SSTs failed to reproduce this structure. The numerical results indicate that these AAM structures are related to SST variations associated with transitions between different phases of the ENSO cycle and have both propagating and standing components. The largest zonal wind contribution from the levels studied (850, 500, and 200 hPa) is at 200 hPa, where the tropical convective outflow is the strongest. Composites of zonal wind and geopotential height show a clear relationship between the stages of the global AAM oscillation and the ENSO cycle. The strong similarity between the simulated and observed AAM series attests to the model's ability to realistically simulate the interannual response of the atmosphere to ENSO SST anomalies.

Mo, Kingtse C.↗
NASA NTRS1994

Ozone and stratospheric height waves for opposite phases of the QBO

The stratospheric quasi-biennial oscillation (QBO) provides an important source of interannual variations in the Northern Hemisphere. O'sullivan and Salby (1990) related extra-tropical eddy transport with the phase of the tropical QBO. When the tropical wind is easterly, the zero wind line is shifted into the winter hemisphere. Enhanced wave activity in middle latitudes acts to weaken the polar vortex. When the tropical wind is in the westerly phase the situation reverses. Heights at 30 mb and ozone configurations are contrasted in this paper for these two QBO phases. When the winter vortex deforms due to the amplification of planetary waves 1 and 2, extends westward and equatorward, the complementary band of low vorticity air spirals in toward the pole from lower latitudes. Sometimes, these planetary waves break (Juckes and McIntyre, 1987) and an irreversible mixing of air takes place between high and mid-latitudes. Global ozone patterns, as obtained form satellite observations, appear to be affected by planetary wave breaking (Leovy et al. 1985). This mixing results on regions with uniform ozone and potential vorticity. In the Southern Hemisphere (SH), Newman and Randel (1988) using Total Ozone Mapping Spectrometer (TOMS) data and the NMC analyses have found strong spatial correlation between the October mean temperature in the lower stratosphere and total ozone for the 1979 through 1986 years. Recently Nogues-Paegle et al.(1992) analyzed SH ozone and height data from 1986 to 1989. They found that leading empirical orthogonal functions (EOFs) for both ozone and 50 mb heights exhibit zonal wave 1 and 2 and that the correlations between ozone and 50 mb principal components (PCs) are high. The results were found to be consistent with a linear planetary wave advecting a passive tracer. In this paper, the dominant patterns of variability for 30 mb NMC heights and TOMS total ozone are obtained for the winter to summer transition (January to May) in the Northern Hemisphere (NH) for the years 1987-1990.

Mo, Kingtse C.↗
NASA NTRS1992

Low-frequency predictability of the Dynamical Extended-Range Forecast Experiment

The objective of the study was to analyze data from the Dynamical Extended-Range Forecast Experiment conducted from January 1986 to March 1987, and to evaluate differences between analysis and forecasts with emphasis on the tropical 30-50-day oscillation. The diagnostic toll used is the projection of analysis and forecast data onto the normal modes of a primitive equation model. Examination of zonal-wind anomalies in the tropics shows that the forecast model predicts propagation of intraseasonal variations more accurately for slow propagation rates. The forecast amplitude is generally weaker than the analyzed amplitude. Analyzed kinetic energy and error fields exhibit similar horizontal scales for internal and external modes. External Rossby-mode components maximize in the extratropics while Rossby internal modes exhibit patterns that extend over the entire globe.

Nogues-Peagle, Julia↗
NASA NTRS1992

Lower stratosphere waves during 1986-1989 southern springs

Global NMC height analyses and Nimbus 7 TOMS Grid-T Version 6 data are used to investigate the horizontal structure of ozone and 50-mb height waves for the 1986-1989 springs of the Southern Hemisphere. Empirical orthogonal functions (EOFs) are obtained for the ozone and height data independently to identify the meridional structure of observed long waves as well as their propagation characteristics. The leading EOFs for both the ozone and 50-mb height waves exhibit wavenumber 1 and 2 patterns. The correlation coefficients between ozone and 50-mb height principal components are high. They indicate high/low ozone values associated with high/low values of 50-mb heights. This distribution is consistent with the advection of ozone by planetary waves south of the ozone maximum, as shown by a simple linear wave model. The observed total ozone amplitudes for waves 1 and 2 for most years are consistent with the total ozone predictions by the wave model.

Nogues-Paegle, Julia↗
NASA NTRS1990

Statistical significance test for transition matrices of atmospheric Markov chains

Low-frequency variability of large-scale atmospheric dynamics can be represented schematically by a Markov chain of multiple flow regimes. This Markov chain contains useful information for the long-range forecaster, provided that the statistical significance of the associated transition matrix can be reliably tested. Monte Carlo simulation yields a very reliable significance test for the elements of this matrix. The results of this test agree with previously used empirical formulae when each cluster of maps identified as a distinct flow regime is sufficiently large and when they all contain a comparable number of maps. Monte Carlo simulation provides a more reliable way to test the statistical significance of transitions to and from small clusters. It can determine the most likely transitions, as well as the most unlikely ones, with a prescribed level of statistical significance.

Vautard, Robert↗
NASA NTRS1989

Empirical orthogonal functions and multiple flow regimes in the Southern Hemisphere winter

A new empirical orthogonal function (EOF) analysis of winter 500 mb geopotential height anomalies in the Southern Hemisphere is presented. An earlier EOF analysis prefiltered the anomalies to exclude wavenumbers 5 and higher; the present analysis does not. The different preprocessing of data affects the results. All three distinct planetary flow regimes identified in the winter circulation of the Southern Hemisphere by a pattern correlation method are captured by the new set of EOFs; only two of those regimes were captured by the earlier set. The new results, therefore, lend further support to the idea that EOFs point to distinct planetary flow regimes.

Farrara, John D.↗
NASA NTRS1987

A GCM study on the maintenance of the June 1982 blocking in the Southern Hemisphere

GCM experiments are used to study several possible mechanisms associated with the maintenance of the June 1982 blocking in the Southern Hemisphere. The mechanisms considered include changed orography, sea surface temperature anomalies, tropical heating, regional heating in the Pacific area, land-sea contrast, and sensible heating in the Antarctic area. It is concluded that asymmetric heating due to land-sea contrast was the most important boundary forcing associated with maintenance of the block. A 'no Australia' experiment confirms this result and suggests that local land-sea contrast kept the block stationary. High-latitude sensible heating associated with cold air outbreaks from Antarctica was also important in maintaining the block.

Mo, Kingtse C.↗
NASA NTRS1987

Statistics and dynamics of persistent anomalies

Persistent anomalies with recurrent spatial patterns play an important role in the atmosphere's low-frequency variability. A connection between statistical and dynamical methods of description and prediction of persistent anomalies is established by computing and analyzing the empirical orthogonal functions (EOFs) in a simple deterministic model, on the one hand, and in Southern Hemisphere geopotential heights, on the other. The dynamical model is governed by the fully nonlinear, equivalent-barotropic vorticity equation on the sphere, with simplified forcing, dissipation and topography. The Southern Hemisphere data consist in gridded daily maps of 500 mb heights from June 1972 to July 1983. Two types of persistent anomalies appear in this time series, both having a strong wavenumber-three component; they differ by the value of the constant phase of this wave and by the strength of the wavenumber-one component. The first two EOFs bear a striking resemblance to these two patterns. It is concluded that the dynamical interpretation of EOFs is their pointing from the time mean to the most populated regions of the system's phase space. Pursuing this interpretation, a Markov-chain formulation of transitions from one persistent anomaly regime to another is introduced, and the implications for long-range forecasting are discussed.

Mo, Kingtse C.↗
NASA NTRS1986

Tropical-extratropical geopotential height teleconnections during the Northern Hemisphere winter

Simultaneous and lagged correlation patterns between height anomalies in the Northern Hemisphere (NH) or in the Southern Hemisphere (SH) and height anomalies at tropical stations in two major tropical precipitation zones (the Indochina maritime continent and Africa) were examined. The height anomalies among the tropical stations in these zones and its nearby Pacific Ocean, South America, and Africa are strongly correlated; they are also correlated with stations in Australia and the North PLacific Ocean. The correlations between height anomalies at any of these stations and NH height anomalies show a well-defined global pattern with major features concentrated in the United States and adjacent oceans. Depending upon the location of the stations, the pattern is either a Pacific North American (PNA), a Tropical NH (TNH), or a mixed pattern having both elements. During the El Nino/Southern Oscillation (ENSO) years both TNH and PNA patterns appear in simultaneous and lagged maps, but in non-ENSO years the TNH is weak in simultaneous charts.

Mo, Kingtse C.↗