Global Variations in Water and Energy Diurnal Cycles

1. Global Variations in Water and Energy Diurnal Cycles Alex Ruane John Roads Masao Kanamitsu

2. Outline • Introduction and Background • The Coordinated Enhanced Observing Period • Diurnal Methodology • Simulated Variations in the Energy Cycle • Simulated Variations in the Water Cycle • Comparison with Observations

3. Motivation • An exploration of the dominant balances, exchanges, and dynamics of the water and energy diurnal cycles over regions with unique diurnal behavior is lacking • How do different components of the water and energy cycles react to the diurnal signal in different parts of the globe? • What drives regional consistency in diurnal behavior? • How do model parameterizations perform on the diurnal scale? • Global models tend to be tuned with a focus on the long-term mean at the expense of extreme events • Too much drizzle, not enough floods or droughts • Too many warm days, not enough heat waves • This examination will help identify model error, as well as improve our ability to simulate the diurnal cycle

4. The Coordinated Enhanced Observing Period • CEOP takes advantage of ongoing GEWEX continental-scale experiments and new Earth-observing satellite products to examine our ability to understand and model the water cycle • 3½ year observation period • 41 highly-observed reference sites • 6 remote sensing centers • 10 modeling centers ECPC contributions to CEOP: 2 Model Versions: - NCEP/DOE Reanalysis-2 (RII) - ECPC’s Seasonal Forecast Model (SFM) reanalysis 2 Experiment Types: - 6-hr Analysis runs initialized at 00, 06, 12, and 18 UTC with 3-hr resolution - 36-hr Forecast runs initialized at 12 UTC with 3-hr resolution Source: CEOP Implementation Plan

5. Harmonic Analysis Actual (red) and Harmonic Fit (blue) for July, August, and September 2001 Latent Heat Flux at grid point in China over entire period (left) and mean diurnal cycle (right) • Annual, diurnal, and semidiurnal harmonics least-squares fit onto individual seasons. • Process emphasizes the phase and relative amplitudes of the harmonics, not as accurate for actual magnitude. • Affected by strength of other frequencies and extreme events • Amplitude divided by standard deviation to determine the strength of the signal Actual (red) and Harmonic Fit (blue) for July, August, and September 2001 Precipitation Rate at grid point in China over entire period (left) and mean diurnal cycle (right)

6. Phase & Amplitude Maps Phase Amplitude / Standard Deviation

7. Global Diurnal Variations in Energy • Global views reveal consistency of budget components’ diurnal cycles • Diurnal behavior of many land surface energy variables appear to be independent of location, depending only on local thermodynamics • Are we missing surface interactions that would alter lags? • Land and ocean regimes immediately evident in many energy components’ diurnal cycles • Differences in phase, amplitude, and regional consistency • Coastal patterns suggest dynamical interaction between regimes 2001-2003 July, August, and September phase and normalized amplitude of diurnal harmonics for latent heat flux and 2-meter temperature Color = phase of peak precipitation Intensity = amplitude of peak

8. Diurnal Variations in Vertical Profiles ARM SGP Summertime Diurnal Potential Temperature Anomalies ARM SGP Summertime Wind Speed Anomalies • Lower atmosphere heated from below on diurnal timescales, while upper atmosphere reacts more to the radiative heating • Many interesting structures to examine in the evolution of the vertical profile • Vertically propagating heat wave affects stability • The wind speed has a nocturnal maximum, which is counter the expected continental afternoon maximum found by Dai and Deser (1999) • Diurnal structures formed in large-scale override the ARM SGP thermodynamics • Mountain/Valley circulation from the Rockies extends all the way into Oklahoma boundary layer

9. Global Diurnal Variations in Water • Large spatial variation in the diurnal cycle of both reservoir and flux terms of the water cycle • Much more dependent on regional dynamics than energy terms • Latitudinal contrasts • Land/ocean (and coastal) contrasts • Seasonal contrasts • Mountain/Low-lying contrasts 2001-2003 July, August, and September phase and normalized amplitude of diurnal harmonics for precipitable water and precipitation Color = phase of peak precipitation Intensity = amplitude of peak

10. Diurnal Variation in Vertical Profiles ARM SGP Summertime Diurnal Specific Humidity Anomalies ARM SGP Summertime Precipitation Heating Anomalies • Boundary layer moisture propagates up from surface evaporation • Upper atmosphere reacts to convective signal • Afternoon convection initiates from ~0.85σ level at top of boundary layer • Extends throughout upper troposphere, with most energy released above ~0.75σ and secondary diurnal peak near tropopause

11. Comparison with ARM SGP Observations • The experiments do a decent job of matching the radiation and surface fluxes • Water cycle and soil processes need improvement • Some dynamical features are completely missed Blue = observations Green = RII6 Red = RII36

12. Comparison with TRMM • Experiments reproduce afternoon maxima over the continents and nocturnal maxima over the oceans • Simulations often lead observations • Several regional features reproduced • Experiments have some differences, particularly over mountainous areas and tropics June, July, and August 1998-2002 TRMM Diurnal Cycle of Precipitation, from Nakamura (2004) July, August, and September2001-2003 RII6 Diurnal Cycle of Precipitation July, August, and September 2001-2003 RII36 Diurnal Cycle of Precipitation

13. Comparison with NARR July, August, and September2001-2003 NARR Diurnal Cycle of Precipitation • The North American Regional Reanalysis (NARR) resolves many of the regional features that the global models miss. • Arakawa-Schubert schemes tend to precipitate too early in GSMs • The three dimensional structure of these diurnal features is quite complex, and can be examined as it evolves. July, August, and September 2001-2003 NARR Cross Section for Diurnal Cycle of Zonal Wind

14. Conclusions • The model experiments produce many interesting diurnal features • The surface energy cycle’s diurnal variation is dictated mostly by local thermodynamics • Column energy and water diurnal variations have regional influences through diurnal dynamical structures • Geographically consistent regimes emerge • Land/Ocean contrast • Mountain/Low-Lying differences • Summer/Winter variations • Many questions remain: • What determines lag between different budget components? • What causes the spatial variations in diurnal behavior? • What is the role of regional dynamics, and how are they generated on diurnal time scales?