Linking Weather And Climate

Questions asked at beginning of lecture Tropical Meteorology I (MET 5533) Spring 2010

Selected Questions:

    Zonally Symmetric and Asymmetric Tropics

  1. Why do jets maximize at 200mb?
  2. What happens to the vertical shear in tropical easterlies from DJF to JJA?
  3. Temp gradients are weak in the tropics but are the virtual temperature gradients weak? Why?
  4. What was the stream function defined to satisfy?
  5. How is sensible heat transported by Hadley cell?
  6. What are the three cells that transport heat across the EQ?
  7. Kou-Eliassen equation describes what cell?
  8. What are the two opposing terms in the K-E equation?
  9. What is an atmospheric reanalysis?
  10. In Waliser (1999), what was the purpose of using sub-sampled reanalysis?
  11. What did the difference in sub-sampled reanalysis and in-situ show?
  12. What was found in terms of the effects of data sparseness on the meridional cells?
  13. What was found in terms of the effects of model bias on the meridional cells?
  14. Which ocean is the most zonally asymmetric in the tropics?
  15. What are some zonal asymmetries at 200mb?
  16. What are some zonal asymmetries at 850mb?
  17. Test question: What is Clausius-Clapeyron equation?
  18. What were some of the asymmetric features in rainfall?
  19. Why is the zero line of net radiation north of the equator?
  20. The spatial distribution of net radiation is similar to what other flux?
  21. The net radiation is balanced by what other contribution in the tropics over land?
  22. Would this hold true for the ocean?
  23. Why are there clear skys in the subtropics?
  24. What compensates for the subsidence warming in the subtropics?

  25. Monsoons and Indian Ocean Variability

  26. What is heat flux?
  27. What is the density of sea water?
  28. What is the specific heat capacity of sea water?
  29. How much heat is generated in the atmosphere during the monsoon?
  30. How much energy is transported from the southern Indian Ocean?
  31. What is the mechanism for this ocean transport?
  32. Why do we care about the monsoons?
  33. What is the equivalent of Mascarene High in the northeast monsoon?
  34. What is the equivalent of the West Pacific High of the north east monsoon in the southwest monsoon?
  35. How would you define onset with meridional temperature gradient?
  36. What is the cause of the rapid cooling of the Arabian SSTs?
  37. At what level do we see the largest Psi/Chi interactions?
  38. What does the dot product of stream function and velocity potential gradients (Psi/Chi) tell us?
  39. Why would monsoon onset be considered a planetary phenomenon?
  40. What are the two subtitle things that monsoon evolution is sensitive to?

  41. Gill Atmosphere

  42. What is shallow about the shallow water theory?
  43. What is the phase speed of a Kelvin wave?
  44. What is the phase speed of a Rossby wave?
  45. What is the decay rate of an Equatorial Kelvin wave assume a phase speed of 30m/s?
  46. What is the direction of propagation for these waves?
  47. What is the basis function for global tropics?
  48. What is the basis function for spheres?
  49. Why is the response wider to the east of the source of heating?
  50. What are the assumptions made in the Gill atmosphere?
  51. What is the impact of Newtonian cooling?
  52. What is the impact of Rayleigh damping?
  53. What are the differences in response to the convective heating vs. the mesoscale heating?
  54. Is the net radiation flux up or down over the Arabian Peninsula?
  55. What is the albedo of desert?
  56. How far up in the atmosphere does the surface low extend?
  57. In the thermodynamic budget which term is the weakest over the Arabian Peninsula?
  58. What forms the desert low?
  59. How are the midlat westerlies involved in the desert low?

  60. Interannual variations of the monsoons

  61. What is the basis for climate prediction?
  62. What did Ed Lorenz show in his simple 3-variable model?
  63. What is predictability of the first kind?
  64. What is predictability of the second kind?
  65. Why is predictability of the second kind lower in the tropics?
  66. Why was 1997 monsoon normal despite the fact that the 1998 DJF SST anomalies in eastern pacific +2.3 degrees C?
  67. How was the case made that monsoon was externally and internally forced?
  68. Do you consider the IOD to be an independent mode unique to the Indian Ocean?
  69. Why would you expect a large cross-equatorial heat transport variation from year to year?
  70. What would ensemble do to the variance?
  71. What is Interactive Ensemble?
  72. What is the big difference between TBO and modified TBO?
  73. What was the effect in the Indian Ocean of Interact Ensemble in the COLA model discussed?
  74. What is peculiar about air-sea interaction in Philippines and south China Sea?

  75. Intraseasonal Variability

  76. What is intraseasonal variability?
  77. Which way does the 20-day and 45-day oscillation propagate?
  78. Why is the interannual variability monsoon not due to the shift in the PDF of intraseasonal active/break cycles?
  79. There are more storms in the active phase and fewer in the break of the 45-day oscillation, however, we do not see this in the 20-day oscillation simply because the number of days between phases is relatively short. Do you expect such variability of storm activity at interannual scales?
  80. Where are MJO anomalies barotropic?
  81. Which of the two oscillations (20- or 45-day) has a stronger relationship with SST?
  82. Where are the intraseasonal anomalies not propagating?
  83. The atmospheric forcing of SST is found more frequently where?
  84. Why do persistent SST model experiments have poor skill in predicting MJO?
  85. What is the main assumption that is made in an identical twin experiment?
  86. What was the objective of doing persistent SST experiment?
  87. What is characteristic of the late summer intraseasonal oscillation?
  88. What is the theory put forward for the northward propagation of these intraseasonal anomalies?
  89. What happened when the Met office increased the vertical resolution in there model?
  90. What is the MJO index?

  91. Monsoon In a Changing Climate

  92. What are the two primary reasons put forth for the breakdown of the monsoon-ENSO teleconnection?
  93. Why does drought happen only when there is a warm phase of ENSO but not every time there is a warm phase?
  94. Why is the seasonal mean central India rainfall not changing over the years?
  95. What is the natural reason for the failing for the Monsoon-ENSO teleconnection?
  96. Why is there a 50-60 year period for IMR and ENSO and a 15-20 year period for the correlation between IMR and ENSO?
  97. How was it shown that Monsoon influences ENSO in the Kirtman-Shukla study?
  98. What is the difference in the impact of monsoon between warm and cold events?
  99. What does a prescribed strong monsoon do to a warm ENSO event?
  100. What does a prescribed weak monsoon do to a warm ENSO event?

  101. ITCZ

  102. Does the winds cross the equator from North to South in the Eastern Pacific any time of the year?
  103. When does the southern limb of ITCZ rain most in Eastern Pacific?
  104. What happens to ITCZ north of the equator [in Eastern Pacific] in spring?
  105. What is (Conditional Instability of the Second Kind) CISK?
  106. What is Ekman frictional convergence; what are the two forces?
  107. Why does CISK promote ITCZ at the poles?
  108. What was the contracting influence to CISK to bring ITCZ to equator?
  109. What nullified the CISK theory of ITCZ?
  110. What was the other effect of f?
  111. What are the assumptions made in Chao and Chen (2004) model to discuss the theory of the ITCZ?
  112. Why did the interactive radiation move the ITCZ away from the equator?
  113. What happens when we specify the surface wind speed to be constant and at 5m/s?
  114. Why is the ITCZ north of the equator in E.Atlantic?
  115. Why is the ITCZ north of the equator in E.Pacific?
  116. What are the two quantities that stratus clouds are dependent on?

  117. ENSO

  118. Where is Nino1+2?
  119. Where is Nino4?
  120. How does CPC define ENSO?
  121. What is the major consequence of this definition?
  122. What were some of the issues with the Nino1+2 index?
  123. What were some of the issues with the Nino4 index?
  124. What does TAO/TRITON buoy array measure?
  125. What causes the cold equatorial tongue in the Pacific? Why does it appear in the east and not the west?
  126. Give three examples of the surface currents in the Equatorial Pacific.
  127. What are the speeds of these currents and the equatorial under current?
  128. What are the 3 fundamental variables that you would look for in a model before investigating any feature on its ENSO simulation?
  129. What is the second order of things to look at?
  130. When is the SST warmest in east Pacific and when is it coldest?
  131. When is the flow at surface over east Pacific westerly and northerly?
  132. When is the flow at surface over easterly and southerly?
  133. What is seasonal phase locking of ENSO variations?
  134. What do regressions of Nino 3 SST on tropical pacific SST tell you?
  135. What are two variations of the thermocline?
  136. What is Sverdrup Balance?
  137. What is a common problem in simulating the second mode of variability of thermocline depth?
  138. What is a consequence of this problem?
  139. How would you determine the duration of a typical ENSO in a model?
  140. What do regressions of Nino 3 SST on equatorial pacific SST at different lead-lags physically signify?
  141. What do regressions of Nino3 SST on thermocline depth anomalies show at different lead-lags?
  142. What are we looking for in regressions of Nino3 SST with global tropical oceans?
  143. What do regressions of Nino3 SST with zonal wind stress anomaly indicate?
  144. What do regression of Nino3 SST with rainfall show?
  145. What is the Pacific/North American Pattern (PNA)?
  146. What is Bjerkness mechanism?
  147. What is the delayed oscillator theory (DOT)?
  148. What is fast SST/slow wave mode theory (FSSW)?
  149. How was the Slow SST/fast wave limit (SSFW) disproved?
  150. What was Mark Cane’s contribution to DOT?
  151. What is the role of off-equatorial Rossby waves?
  152. How do we diagnose inversion clouds?
  153. What is the remote influence of smoothing the status clouds?
  154. Why do you have a La Nina state in a simplified atmospheric model coupled to a full ocean model?
  155. Why do you have the opposite in a complex atmospheric model coupled to a slab ocean model?

  156. Tropical Atlantic Variability

  157. When does Nino I in the Atlantic peak?
  158. When does Nino II in the Atlantic peak?
  159. When does the meridional mode peak?
  160. What is the big difference in annual cycle of SST in Atlantic and Pacific?
  161. What is the difference of the annual cycle of the equatorial zonal wind stress in the two oceans?
  162. What is tropospheric temperature mechanism of SST warming?
  163. Why is the ENSO-tropical Atlantic teleconnection fragile?
  164. Define North Atlantic Oscillation (NAO).
  165. What is inter-hemispheric mode?

    Zonally Symmetric and Asymmetric Tropics

  1. Why do jets maximize at 200mb?
  2. There should be some jet because of the thermal wind relationship (The thermal wind is a vertical shear in the geostrophic wind caused by a horizontal temperature gradient. Its name is a misnomer, because the thermal wind is not actually a wind, but rather a wind gradient.) There is a level where the gradient goes to zero, the tropopause, this is where the maximum winds occur.


  3. What happens to the vertical shear in tropical easterlies from DJF to JJA?
  4. Upper level easterlies are weaker in the winter so vertical shear increases in JJA.


  5. Temp gradients are weak in the tropics but are the virtual temperature gradients weak? Why?
  6. The moisture gradient is strong and the maximum is centered in the tropics.


  7. What was the stream function defined to satisfy?
  8. The mass continuity equation.


  9. How is sensible heat transported by Hadley cell?
  10. advection by the Hadley cell occurs from the winter to summer hemisphere near the surface and from summer to winter at the top of the troposphere. Sensible heat is therefore transported from the winter to summer hemisphere. However, potential energy is transported from summer to winter at a greater magnitude making enthalpy net transport toward the winter hemisphere.


  11. What are the three cells that transport heat across the EQ?
  12. The Hadley cell, standing eddies, and transient eddies.


  13. Kou-Eliassen equation describes what cell?
  14. The Hadley Cell.


  15. What are the two opposing terms in the K-E equation?
  16. Eddy momentum flux and total heat flux.


  17. What is an atmospheric reanalysis?
  18. A retrospective data assimilation method.


  19. In Waliser (1999), what was the purpose of using sub-sampled reanalysis?
  20. To determine the impacts of model bias and sparse data.


  21. What did the difference in sub-sampled reanalysis and in-situ show?
  22. The model bias in the reanalysis.


  23. What was found in terms of the effects of data sparseness on the meridional cells?
  24. The subsidence region of the Hadley cell was not as well defined in the in-situ data; the southern hemisphere Hadley cell does not extend to 200mb; and the Farrell cell is very broad in the southern hemisphere in-situ data.


  25. What was found in terms of the effects of model bias on the meridional cells?
  26. By comparing in-situ data to sub-sampled reanalysis the effects of model bias are seen. The Hadley cell was seen to be 20%-30% stronger in the model.


  27. Which ocean is the most zonally asymmetric in the tropics?
  28. Based on SSTs, the Pacific Ocean is the most asymmetric. Atlantic is the most zonally symmetric in the tropics.


  29. What are some zonal asymmetries at 200mb?
  30. In the boreal summer there is the Tibetan High, Mexican High, and West african high. In boreal winter there is the West Pacific High, Bolivian High (counterpart of the Tibetan High), and Siberian High. in both summers there is a mid-oceanic trough. These asymmetries are caused by land-ocean contrasts and within land, arid/monsoon contrasts.


  31. What are some zonal asymmetries at 850mb?
  32. Near the surface there is the southwesterly, cross-equatorial monsoon. The Somali jet, subtropical highs, and pacific trades are also seen here.


  33. Test question: What is Clausius-Clapeyron equation?
  34. Saturation vapor pressure related to the temperature of the air mass. Specific humidity is lower over the ocean than land in summer because the land temperatures are higher.

    Show Equation
  35. What were some of the asymmetric features in rainfall?
  36. Precipitation is all asymmetric. Major features include the monsoons, ITCZ, and other convergence zones.


  37. Why is the zero line of net radiation north of the equator?
  38. The short answer is that there is more land mass in the Northern hemisphere. The long answer is that the thermal inertia of water is greater offsetting the seasonality of solar radiation making the thermal equator to the north.


  39. The spatial distribution of net radiation is similar to what other flux?
  40. Net solar radiation absorbed at TOA.


  41. The net radiation is balanced by what other contribution in the tropics over land?
  42. Latent heat of condensation (from monsoons).


  43. Would this hold true for the ocean?
  44. No, because there is a transport of heat via ocean currents.


  45. Why are there clear skys in the subtropics?
  46. This is the location of the sinking branch of the Hadley cell.


  47. What compensates for the subsidence warming in the subtropics?
  48. Radiative cooling would be the most-guessed wrong answer. Baroclinic eddies organized through storm tracks and quasi-stationary waves transport energy pole ward, thus compensating for the subsidence warming from the descending branch of the Hadley cell.


    Monsoons and Indian Ocean Variability

  49. What is heat flux?
  50. The transport of energy per unit area per unit time.


  51. What is the density of sea water?
  52. 1027kg/m^3


  53. What is the specific heat capacity of sea water?
  54. Sea water: 3994 J/kgK which is less than water: 4185 J/kgK


  55. How much heat is generated in the atmosphere during the monsoon?
  56. About 1.5 petawatts


  57. How much energy is transported from the southern Indian Ocean?
  58. 1.5 petawatts - it balances!


  59. What is the mechanism for this ocean transport?
  60. Ekman transport.


  61. Why do we care about the monsoons?
  62. First, we need to stop being parochial and only concern ourselves with local events. Second, the Hadley and Walker cells are nothing more than monsoons. Furthermore, the onset of the monsoon is so spectacular it effects the entire globe.


  63. What is the equivalent of Mascarene High in the northeast monsoon?
  64. Siberian High because both are low-level pressure systems (850mb).


  65. What is the equivalent of the West Pacific High of the north east monsoon in the southwest monsoon?
  66. The Tibetan High as both are 200mb pressure systems.


  67. How would you define onset with meridional temperature gradient?
  68. The gradient changes from negative to positive.


  69. What is the cause of the rapid cooling of the Arabian SSTs?
  70. Upwelling and evaporation.


  71. At what level do we see the largest Psi/Chi interactions?
  72. At the lower level.


  73. What does the dot product of stream function and velocity potential gradients (Psi/Chi) tell us?
  74. When they are parallel, the divergent (irrotational) circulations will transfer energy to the non-divergent circulations.


  75. Why would monsoon onset be considered a planetary phenomenon?
  76. The spectrum is dominated by wave numbers 0 and 1.


  77. What are the two subtitle things that monsoon evolution is sensitive to?
  78. The orientation of the divergent component of the wind and diabatic differential heating.


  79. What is shallow about the shallow water theory?
  80. The horizontal scale is much larger than the vertical scale.


  81. What is the phase speed of a Kelvin wave?
  82. (gh)^1/2


  83. What is the phase speed of a Rossby wave?
  84. -Beta/(k^2 + l^2) If it takes two months for a Kelvin wave to propagate across the ocean it will take 6 months for the Rossby wave.


  85. What is the decay rate of an Equatorial Kelvin wave assume a phase speed of 30m/s?
  86. About 1600km: y_c = (2c/Beta)^1/2


  87. What is the direction of propagation for these waves?
  88. The Kelvin waves propagate east and Rossby waves west.


  89. What is the basis function for global tropics?
  90. Parabolic cylinder.


  91. What is the basis function for spheres?
  92. Spherical harmonics a.k.a Legendre polynomials in the y direction and Fourier transform in the x.


  93. Why is the response wider to the east of the source of heating?
  94. The Kelvin wave moves 3 times faster so the response is wider.


  95. What are the assumptions made in the Gill atmosphere?
  96. 1 steady state atmosphere; 2 free surface and fixed bottom; 3 the forced motion is sufficiently weak that it can be treated by linear dynamics; 4 solutions are for long waves not gravity waves; 5 sinusoidal heating profile; 6 the thermal damping is Newtonian cooling; 7 the friction is Rayleigh damping; 8 the thermal and frictional damping rates are assumed to have the same time scale everywhere; 9 Beta plane approximation.


  97. What is the impact of Newtonian cooling?
  98. Homogenizes the atmospheric motion in vertical, and a strong vertical uniform wind is found below the heat source; adding any momentum damping removes an surface wind response to the elevated heat source.


  99. What is the impact of Rayleigh damping?
  100. Localizes the heat source.


  101. What are the differences in response to the convective heating vs. the mesoscale heating?
  102. MC: shallower, moves slower, dissipates faster
    CH: deeper and more uniform, moves faster, dissipates slower
    Recall that the depth/speed diagram was a positive sloped line.


  103. Is the net radiation flux up or down over the Arabian Peninsula?
  104. Up, due to the lateral transport of energy from the monsoons and subsidence that occurs.


  105. What is the albedo of desert?
  106. 40%


  107. How far up in the atmosphere does the surface low extend?
  108. 800mb


  109. In the thermodynamic budget which term is the weakest over the Arabian Peninsula?
  110. Horizontal advection, because the thermal gradient is weak.


  111. What forms the desert low?
  112. Because there is asymmetric heating in the monsoon, there is only a Rossby wave response.


  113. How are the midlat westerlies involved in the desert low?
  114. Equivalent potential temp surface slopes toward the monsoon region producing adiabatic warming.

    Interannual variations of the monsoons

  115. What is the basis for climate prediction?
  116. It is the predictability of the second kind meaning that the predictability is a function of the boundary conditions not on initial values.


  117. What did Ed Lorenz show in his simple 3-variable model?
  118. Chaos theory; that forecasts are an initial value problem. The forecast prediction is sensitive to conditional sensitivity; a small perturbation in the initial conditions can lead to a large change in the forecast.


  119. What is predictability of the first kind?
  120. Weather: Predictability whose source is knowledge of the initial conditions and which is limited by the flow itself.


  121. What is predictability of the second kind?
  122. Climate: Predictability whose source is based on knowledge of the boundary conditions.


  123. Why is predictability of the second kind lower in the tropics?
  124. This is false! Predictability of the second kind is higher in the tropics and lower in the midlats because the temperature gradients are weak, instabilities are far less, and changes in saturation vapor pressure are smaller in the tropics.


  125. Why was 1997 monsoon normal despite the fact that the 1998 DJF SST anomalies in eastern pacific +2.3 degrees C?
  126. The positive ENSO was counter acted by the Indian Ocean Dipole (IOD)


  127. How was the case made that monsoon was externally and internally forced?
  128. There is a seasonal persistent component which was assumed external. The correlations of daily rainfall vary somewhat from day to day which indicates internal forcing.


  129. Do you consider the IOD to be an independent mode unique to the Indian Ocean?
  130. The matter is still under debate. However, the argument that IOD is a projection of ENSO seems more convincing.


  131. Why would you expect a large cross-equatorial heat transport variation from year to year?
  132. When the monsoon is weak, the southwesterlies are weak and the Ekman drift is weak so there is less heat transport. When the monsoon is strong, there is more Ekman transport. More latent heat is released in a strong monsoon year and therefore the transport compensates for this.


  133. What would ensemble do to the variance?
  134. It lowers the variance because it is the model noise which causes the variance to be too high particularly in the western equatorial Pacific. The average of noise tends to zero.


  135. What is Interactive Ensemble?
  136. It is an ensemble atmospheric model coupled to an ocean model where the mean value of the ensemble AGCM forces the OGCM and the OGCM forces each member of the AGCM ensemble.


  137. What is the big difference between TBO and modified TBO?
  138. TBO is the advancement of the monsoon in the north-south direction; modified TBO includes ENSO and IOD. *


  139. What was the effect in the Indian Ocean of Interact Ensemble in the COLA model discussed?
  140. The correlation between Nino3.4 SST and Indian Ocean increased (became closer to observations than standard coupled COLA model).


  141. What is peculiar about air-sea interaction in Philippines and south China Sea?
  142. The correlations were negative between rainfall and SST. With rainfall leading SST is when the correlations were largest. That would suggest that the SST evolution (especially in the summer time is govern by the atmospheric forcing)

    Intraseasonal Variability

  143. What is intraseasonal variability?
  144. Anything below 90 days.


  145. Which way does the 20-day and 45-day oscillation propagate?
  146. 20: northwest; 45: northeast


  147. Why is the interannual variability monsoon not due to the shift in the PDF of intraseasonal active/break cycles?
  148. Strong or weak year cases are a function of the non-oscillatory eigenmodes, a.k.a. interannual, (3,4,5) not the 20- and 45- day osciilations (6,7) and (1,2) respectively.


  149. There are more storms in the active phase and fewer in the break of the 45-day oscillation, however, we do not see this in the 20-day oscillation simply because the number of days between phases is relatively short. Do you expect such variability of storm activity at interannual scales?
  150. No, there is not a shift in the PDF of intraseasonal activity on interannual scales therefore there will not be more storms in a strong monsoon year. Historical evidence also shows there is not a difference between weak and strong years and the number of storms produced.


  151. Where are MJO anomalies barotropic?
  152. In the mid-latitudes they are dynamically driven (barotropic). In the tropics they are convectively driven (baroclinic).


  153. Which of the two oscillations (20- or 45-day) has a stronger relationship with SST?
  154. 45-day; the correlations with the 20-day were very weak.


  155. Where are the intraseasonal anomalies not propagating?
  156. East Pacific anomalies


  157. The atmospheric forcing of SST is found more frequently where?
  158. In the subtropics; in the deep tropics (between 10S-10N) the SST is forcing the atmosphere.


  159. Why do persistent SST model experiments have poor skill in predicting MJO?
  160. You need SSTs with intraseasonal variations (coupled air-sea interactions). If you have high frequency SSTs in the forcing then you can reproduce MJO.


  161. What is the main assumption that is made in an identical twin experiment?
  162. The model is perfect and has no biases.


  163. What was the objective of doing persistent SST experiment?
  164. To see how well the prediction is with good initial conditions. How long will the anomalies that existed at the initial time persist and provide skill over climatological monthly mean SST.


  165. What is characteristic of the late summer intraseasonal oscillation?
  166. It is mostly over the western pacific, there is a jump from eastern Indian Ocean to the western Indian Ocean.


  167. What is the theory put forward for the northward propagation of these intraseasonal anomalies?
  168. The Rossby waves were travelling northwestward and mixed Rossby-gravity waves were travelling northeastward.


  169. What happened when the Met office increased the vertical resolution in there model?
  170. Higher vertical resolution leads to better convection in the model. This was because the melting layer was being resolved; this 600-500mb layer has increased stability after ice falls through it which will suppress the convection allowing moist static energy to build up until the next active phase of the MJO. The suppression of convection also leads to detrainment of moisture below that layer (trimodal distribution of clouds – shallow, mid-level, and deep convective). Before then it was either shallow or deep convection.


  171. What is the MJO index?
  172. The variance of the zonal wind at 200mb averaged between 10S-10N

    Monsoon In a Changing Climate

  173. What are the two primary reasons put forth for the breakdown of the monsoon-ENSO teleconnection?
  174. 1 The Walker circulation shifted. The zonal mean flow has linearly increased in the recent decades at the expense of the MJO 2 snowpack is less over Siberia in a warming environment (global warming) because the ground temperatures are rising. Less snow means the land is warmer and land-sea contrast has increased so the monsoon is dictated less by external forcing.


  175. Why does drought happen only when there is a warm phase of ENSO but not every time there is a warm phase?
  176. The monsoon fails when there is an eastern Pacific warm event because the sinking branch of the Walker cell is right over India. During a central Pacific warm event the maximum upper-level convergence is more westward.


  177. Why is the seasonal mean central India rainfall not changing over the years?
  178. Because the strong events are becoming more common but the weak to moderate events are less common.


  179. What is the natural reason for the failing for the Monsoon-ENSO teleconnection?
  180. There is an interdecadal oscillation of the walker circulation that modulates the teleconnection.


  181. Why is there a 50-60 year period for IMR and ENSO and a 15-20 year period for the correlation between IMR and ENSO?

  182. The phase of the interdecadal oscillation of SST provides a "boost" to the same phase of ENSO influencing Indian monsoons. That is, when the Interdecadal oscillation is positive, and the ENSO phase is warm, then the two combined will created an very dry monsoon than if the interdecadal phase was negative. For the negative phase of the interdecadal oscillation, the cold ENSO phase is enhanced causing flooding in the monsoon region.


  183. How was it shown that Monsoon influences ENSO in the Kirtman-Shukla study?
  184. By first finding the component of wind stress in the pacific caused by monsoon, they prescribed a wind stress anomaly and found the effects it had on the phases of ENSO.


  185. What is the difference in the impact of monsoon between warm and cold events?
  186. The impact is systematically weaker for the cold phase.


  187. What does a prescribed strong monsoon do to a warm ENSO event?
  188. It weakens the event; easterly anomaly will act against the warm phase.


  189. What does a prescribed weak monsoon do to a warm ENSO event?
  190. Strengthens and lengthens it; the westerly anomaly is a positive feedback allowing the warm event to continue longer than usual.

    ITCZ

  191. Does the winds cross the equator from North to South in the Eastern Pacific any time of the year?
  192. No. Deszoeke (2008) illustrates that the zonally averaged winds in the eastern Pacific are southeasterly all year.


  193. When does the southern limb of ITCZ rain most in Eastern Pacific?
  194. Rain is at a maximum in the southern branch during MAM but is far less than the rain seen in the northern limb.


  195. What happens to ITCZ north of the equator [in Eastern Pacific] in spring?
  196. The rain diminishes compared to the rest of the year but remains as strong as the southern limb.


  197. What is (Conditional Instability of the Second Kind) CISK?
  198. An incipient disturbance causes Ekman convergence in the boundary layer that fuels the convection which in turn fuels more convergence. There is a positive feedback for Ekman frictional convergence.


  199. What is Ekman frictional convergence; what are the two forces?
  200. Coriolis and Friction.


  201. Why does CISK promote ITCZ at the poles?
  202. The stronger coriolis is the more frictional convergence is favored. Coriolis is at a maximum at the poles.


  203. What was the contracting influence to CISK to bring ITCZ to equator?
  204. There is no moisture at the poles to promote convection! there can be no positive feedback even if there is an incipient disturbance. The high level of moisture near the equator pulls the ITCZ back to the equator.


  205. What nullified the CISK theory of ITCZ?
  206. (Sumi 1992) preformed an aqua planet experiment with uniform SSTs and it produced a single ITCZ at the equator due to inertial stability - not because of increased moisture at the equator.


  207. What was the other effect of f?
  208. Rotation (f) not only feeds CISK but also has inertia stability which resists convection. This can be shown from the vorticity equation. So the reduced rotation at the equator allows convection to occur more freely. Note: the value of f is not what is important but the beta effect – without a gradient of Coriolis there is no preference for the ITCZ to reside at the equator.


  209. What are the assumptions made in Chao and Chen (2004) model to discuss the theory of the ITCZ?
  210. Aqua plant with uniform SST over the globe, Constant solar angle (boreal summer), constant radiative cooling rates.


  211. Why did the interactive radiation move the ITCZ away from the equator?
  212. There is more radiative cooling outside of the ITCZ due to less humidity. So the downward subsidence motion has to become stronger to compensate for this cooling. Exactly the opposite happens within the ITCZ. The Hadley cell becomes stronger which means stronger surface winds and the role of CISK comes into play resulting in ITCZ moving away from the equator. -- Because you have intensified the convection at the ITCZ and enhanced the subsidence, surface winds have increased, convergence must increase. Frictional (Ekman) convergence has to become larger (f must be larger) and so CISK is greater.


  213. What happens when we specify the surface wind speed to be constant and at 5m/s?
  214. Effects of CISK are nullified because there is no positive feedback in response to the convection.


  215. Why is the ITCZ north of the equator in E. Atlantic?
  216. The continental bulge of the West African landmass heats up faster than the ocean and the temperature gradient causes the convection to be stronger in the north moving the ITCZ north.


  217. Why is the ITCZ north of the equator in E. Pacific?
  218. The angle of the coast of Peru causes stronger upwelling than in the north. The colder waters in the south versus the north move the ITCZ north.


  219. What are the two quantities that stratus clouds are dependent on?
  220. Warm SST and lower troposphere stability lead to more clouds.

    ENSO

  221. Where is Nino1+2?
  222. Far eastern south equatorial Pacific.


  223. Where is Nino4?
  224. Western and central equatorial Pacific.


  225. How does CPC define ENSO?
  226. Three month running mean over .5 degree C for 5 months.


  227. What is the major consequence of this definition?
  228. It cannot be used as a prediction tool.


  229. What were some of the issues with the Nino1+2 index?
  230. Strong response to warm events and poor response to cold events. Also has the poorest correlation with SOI.


  231. What were some of the issues with the Nino4 index?
  232. Strong response to cold events.


  233. What does TAO/TRITON buoy array measure?
  234. temperatures and currents to a depth of 500 meters


  235. What causes the cold equatorial tongue in the Pacific? Why does it appear in the east and not the west?
  236. Ekman Divergence. Stronger easterlies and shallow thermocline in the east.


  237. Give three examples of the surface currents in the Equatorial Pacific.
  238. North Equatorial counter current, North and South equatorial current.


  239. What are the speeds of these currents and the equatorial under current?
  240. N. Equatorial counter current - 50 cm/s N. Equatorial current - 40 cm/s S. Equatorial current - 10 cm/s Equatorial under current - 120 cm/s


  241. What are the 3 fundamental variables that you would look for in a model before investigating any feature on its ENSO simulation?
  242. Look at the mean SST to see the warm pool in the west and cold tongue in the east of the equatorial Pacific. Look at the slope of the thermocline depth gradient; should be deep in the west and shallow in the east. Mean precipitation should show modulation of Walker circulation.


  243. What is the second order of things to look at?
  244. Seasonal cycle of SSTs in the eastern Pacific should be robust.


  245. When is the SST warmest in east Pacific and when is it coldest?
  246. They are warmest in boreal spring and coldest in boreal fall.


  247. When is the flow at surface over east Pacific westerly and northerly?
  248. Boreal spring


  249. When is the flow at surface over easterly and southerly?
  250. Boreal fall


  251. What is seasonal phase locking of ENSO variations?
  252. SST variability peak in boreal winter and diminishes in boreal spring with relatively weak variability in the boreal summer and early fall. SST gradient is very strong in SON, so phase locking of ENSO peaks at that time too.


  253. What do regressions of Nino 3 SST on tropical pacific SST tell you?
  254. It shows the spatial pattern of ENSO SST variability. Most models on SST pattern correlation with Nino3 SST extending west dateline.


  255. What are two variations of the thermocline?
  256. Tilt mode which explains ~50% of the variance and the warm water volume mode which explains ~30%. The first is associated with the phase of ENSO, the second is the recharge-discharge of warm water in the equatorial Pacific.


  257. What is Sverdrup Balance?
  258. Positive wind stress curl (westerlies at the equator) = pole ward transport of water. Negative wind stress curl (easterlies at the equator) = equator ward transport of water. Show Equation


  259. What is a common problem in simulating the second mode of variability of thermocline depth?
  260. The nodal line is around 10S instead of south of 20S; the meridional extent of the mode is too small.


  261. What is a consequence of this problem?
  262. The ENSO timescale is too short because the recharge-discharge is occurring too quickly.


  263. How would you determine the duration of a typical ENSO in a model?
  264. The autocorrelation will drop down the e folding scale at the typical length of an event.


  265. What do regressions of Nino 3 SST on equatorial pacific SST at different lead-lags physically signify?
  266. It shows the duration of events, the periodicity of ENSO, and zonal extent of the signal. Models commonly extend to far west and occur to regularly and frequently.


  267. What do regressions of Nino3 SST on thermocline depth anomalies show at different lead-lags?
  268. It shows the eastward propagation of upwelling/downwelling Kelvin wave. It takes about 4 months for Kelvin wave cross the Pacific Ocean.


  269. What are we looking for in regressions of Nino3 SST with global tropical oceans?
  270. We are looking for teleconnection with Indian ocean SST and northern tropical Atlantic SST. Winter Indian Ocean covaries with ENSO.


  271. What do regressions of Nino3 SST with zonal wind stress anomaly indicate?
  272. The meridional width is a reflection of the periodicity of ENSO in the model (narrow = shorter). Also, look to see positive relationship; if not the mechanism of variability is not ENSO.


  273. What do regression of Nino3 SST with rainfall show?
  274. They show the anomalous Walker circulation versus the Hadley circulation.


  275. What is the Pacific/North American Pattern (PNA)?
  276. The 200mb height anomalies forced by the heat source of ENSO. It is a stationary Rossby wave.


  277. What is Bjerkness mechanism?
  278. It is a coupled air-sea interactions lead to the growth of the anomalies. The problem is that is requires an anomaly before it can grow. When the trades weaken, it allows the SST to rise because there is less upwelling and less evaporative cooling. The increases SSTs reduce the temperature gradient slowing the winds further.


  279. What is the delayed oscillator theory (DOT)?
  280. From the westerly wind stress anomaly a down welling Kelvin wave is generated which causes warm SSTs in the east. Eventually the corresponding Rossby wave reflects as an upwelling Kelvin wave which acts to restore conditions to normal. The period of ENSO is too short.


  281. What is fast SST/slow wave mode theory (FSSW)?
  282. It is just another name for the Delayed Oscillator theory.


  283. How was the Slow SST/fast wave limit (SSFW) disproved?
  284. This theory requires that wind stress to be in phase with thermocline depth anomalies. It was found wind stress is not in equilibrium with thermocline depth in the observations as this theory predicted. SSTA was in equilibrium with thermocline depth anomalies.


  285. What was Mark Cane’s contribution to DOT?
  286. His theory suggested that it takes multiple reflections of waves to change the phase of ENSO. The problem with this is the multiple waves are not observed.


  287. What is the role of off-equatorial Rossby waves?
  288. Off-equatorial Rossby waves are much slower than equatorial Rossby waves so they take longer to reach the boundary. The Kelvin waves reelected by these seem to cancel out with the equatorial Kelvin waves. As a result the upwelling Kelvin wave has a reduced amplitude and is less efficient at removing the SST anomalies and so more waves are required (ENSO period is lengthened).


  289. How do we diagnose inversion clouds?
  290. There is an inversion at the cloud top and no convection in the column.


  291. What is the remote influence of smoothing the status clouds?
  292. SST gradients are stronger due to reflection, which gives rise to stronger easterlies at the surface, which induces a La Nina effect (the Walker circulation has moved more to the west).


  293. Why do you have a La Nina state in a simplified atmospheric model coupled to a full ocean model?
  294. It is due to the ocean thermostatic properties. Increasing the warming over the ocean leads to an increased temperature gradient. This means increases winds and more upwelling of cold water in the east.


  295. Why do you have the opposite in a complex atmospheric model coupled to a slab ocean model?
  296. The walker circulation weakens because the moisture content has gone up. The precipitation does not increase at the same rate as moisture therefore the mass flux must decrease.

    Tropical Atlantic Variability

  297. When does Nino I in the Atlantic peak?
  298. JJA


  299. When does Nino II in the Atlantic peak?
  300. OND and is located off the southwest coast of Africa.


  301. When does the meridional mode peak?
  302. MAM


  303. What is the big difference in annual cycle of SST in Atlantic and Pacific?
  304. The Pacific is confined to the east; the Atlantic is over the whole basin. Also, the cold season is shorter in the Atlantic than the Pacific.


  305. What is the difference of the annual cycle of the equatorial zonal wind stress in the two oceans?
  306. The wind stress is strong mainly in the West Atlantic and in the East Pacific.


  307. What is tropospheric temperature mechanism of SST warming?
  308. The warm anomaly in Nino3.4 SST heats the troposphere and spreads quickly in the atmosphere from Kelvin and Rossby waves around the globe. The increase tropospheric temperatures lead to a more stable environment which reduces the convection and circulation which reduces the evaporative cooling at the surface. This is how the SSTs warm along the equator around the globe. OLR also reduces.


  309. Why is the ENSO-tropical Atlantic teleconnection fragile?
  310. There is uncorrelated wind stress variability. When the wind stress is stronger westerly over the West Atlantic there is a strong teleconnection with ENSO. When there are easterlies, there is strong upwelling in the Atlantic and so no teleconnection with ENSO


  311. Define North Atlantic Oscillation (NAO).
  312. It is the anomalous pressure difference between Icelandic polar low and the Azores subtropical high. It is both interannual and interdecadal.


  313. What is inter-hemispheric mode?
  314. Inter-hemispheric is also known as Meridional mode and tropical Atlantic variability. It is a dipole of warming of SSTs between the north and south tropical Atlantic. It is caused by wind induced surface heat fluxes either from ENSO (weakened trades; warmer in the north) or WISHE.

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