Time zones are a special topic. HMI data it time tagged in TAI time, "International Atomic Time", since they are observed on SDO using TAI time. There are no leap-seconds in TAI time as there are in UTC so for long time series such as the 14 year SOHO/MDI set of heliosiesmology data one does not need to worry about the 5 leap-seconds that were inserted during that time. All SDO data are intrinsically observed using TAI. For the convenience of people the times can also be expressed in UTC. HMI data has "nicer" time stamps when expressed in TAI. By choice, AIA uses UTC for most user-level time stamps. Either may be used for any JSOC data requests. Since the offset, now 34 seconds, is more than half the basic HMI obseving cadence of 45 seconds, you will often not get the record you expect if you use UTC to ask for HMI data. The default for an omitted time zone specifier is UTC. Thus if you ask for hmi_test.M_45s[2010.07.25] you will get the magnetogram labelled hmi_test.M_45s[2010.07.25_00:00:45_TAI].
The rule of thumb is: Use TAI when specifing HMI or MDI data but use UTC for AIA.
The full set of PrimeKeys for each series are listed in lookdata both on the "Series Content" tab and at the top of the "RecordSet Select" tab. If you check the checkbox labelled "Check box to show the QueryBuilder" located just under the title "Select Records and Get Record Count" on the "RecordSet Select" tab, lookdata will provide you with an expanded template for building a recordset query using all of the available PrimeKeys.
T_REC [ ] (time-slotted, 45.0) expects TAI
CAMERA [ ] (int)
where clause [? ?] Uses prime key logic
where clause [! !] use disables prime key logic
This example shows what you see with the checkbox checked and the hmi_test.M_45s series selected.
It shows that hmi_test.M_45s has two PrimeKeys, "T_REC" and "CAMERA". HMI has two cameras,
one called 1:Side and the other 2:Front (referring to the location of the electronics box on the HMI
instrument). Since each basic observable such as magnetic field or Doppler velocity can be computed
for data taken by either camera, we indicate the particular camera with the CAMERA PrimeKey. At least
up through July 2010, all 45-second cadence Magnetograms ahve been made using only the Front camera so
we may safely omit the CAMERA keyword in a data request.
Generally, each PrimeKey will be in some sense orthogonal to the others. They specify different quantities which are all needed for a unique record specification. This is not required. In fact, AIA and HMI each use both T_OBS and FSN as PrimeKeys for the "Level-1" dataseries. T_OBS is always the time of observation of a quantity. For the low-level HMI and AIA data, "FSN" is the "Frame Sequence Number" and is a unique number provided by the onboard software when each image is created. Since no two images can be made at exactly the same time, FSN is redundant with T_OBS. However, rounded to the nearest second and in testing multiple images can be obtained with the same T_OBS rounded value. But the reason we chose to use both for this low-level data is that the data is generated based on FSN but used based on T_OBS. You should use "T_OBS" for aia.lev1 data unless you really know what you are after.
While the built-in PrimeKey formats are convenient with notation like "2010.07.25/6h" sometimes the user wants to either build a query from other not Prime Keywords or to make a query that is noyt easy to specify using the PrimeKey special logic. In those cases we provide the ability to specify one or more very geenral SQL "Where" clauses. An SQL where clause contents may be provided in one or more "[? ... ?]" or "[! ... !]" clauses. The word "where" is not needed, or allowed.